Adding support for incremental cluster parsing.

BUG=104160
TEST=Covered by ChunkDemuxer unittests.


Review URL: http://codereview.chromium.org/8775035

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@114030 0039d316-1c4b-4281-b951-d872f2087c98

11 files changed, 793 insertions, 263 deletions

diff --git a/media/filters/chunk_demuxer.cc b/media/filters/chunk_demuxer.cc
index d437d91..f81b80f 100644
--- a/media/filters/chunk_demuxer.cc
+++ b/media/filters/chunk_demuxer.cc
@@ -130,7 +130,7 @@ void ChunkDemuxerStream::Flush() {
 bool ChunkDemuxerStream::CanAddBuffers(const BufferQueue& buffers) const {
   base::AutoLock auto_lock(lock_);
 
-  // If we haven't seen any buffers yet than anything can be added.
+  // If we haven't seen any buffers yet, then anything can be added.
   if (last_buffer_timestamp_ == kNoTimestamp)
     return true;
 
@@ -434,7 +434,7 @@ bool ChunkDemuxer::AppendData(const uint8* data, size_t length) {
     int cur_size = 0;
     int bytes_parsed = 0;
     int result = -1;
-    bool parsed_a_cluster = false;
+    bool can_complete_seek = false;
 
     byte_queue_.Peek(&cur, &cur_size);
 
@@ -449,16 +449,19 @@ bool ChunkDemuxer::AppendData(const uint8* data, size_t length) {
           }
           break;
 
-        case INITIALIZED:
-          result = ParseCluster_Locked(cur, cur_size);
+        case INITIALIZED: {
+          bool buffers_added = false;
+          result = ParseCluster_Locked(cur, cur_size, &buffers_added);
           if (result < 0) {
             VLOG(1) << "AppendData(): parsing data failed";
             ReportError_Locked(PIPELINE_ERROR_DECODE);
             return true;
           }
 
-          parsed_a_cluster = (result > 0);
-          break;
+          // We can complete the seek if we have successfully parsed
+          // some data and buffers were added to one of the DemuxerStreams.
+          can_complete_seek |= (result > 0 && buffers_added);
+        } break;
 
         case WAITING_FOR_INIT:
         case ENDED:
@@ -477,7 +480,7 @@ bool ChunkDemuxer::AppendData(const uint8* data, size_t length) {
 
     byte_queue_.Pop(bytes_parsed);
 
-    if (parsed_a_cluster && seek_waits_for_data_) {
+    if (can_complete_seek && seek_waits_for_data_) {
       seek_waits_for_data_ = false;
 
       if (!seek_cb_.is_null())
@@ -730,7 +733,8 @@ bool ChunkDemuxer::SetupStreams() {
   return !no_supported_streams;
 }
 
-int ChunkDemuxer::ParseCluster_Locked(const uint8* data, int size) {
+int ChunkDemuxer::ParseCluster_Locked(const uint8* data, int size,
+                                      bool* buffers_added) {
   lock_.AssertAcquired();
   if (!cluster_parser_.get())
     return -1;
@@ -749,9 +753,6 @@ int ChunkDemuxer::ParseCluster_Locked(const uint8* data, int size) {
     }
     // Skip the element.
     return result + element_size;
-  } else if (id != kWebMIdCluster) {
-    VLOG(1) << "Unexpected ID 0x" << std::hex << id;
-    return -1;
   }
 
   int bytes_parsed = cluster_parser_->Parse(data, size);
@@ -759,20 +760,25 @@ int ChunkDemuxer::ParseCluster_Locked(const uint8* data, int size) {
   if (bytes_parsed <= 0)
     return bytes_parsed;
 
-  // Make sure we can add the buffers to both streams before we actutally
-  // add them. This allows us to accept all of the data or none of it.
-  if ((audio_.get() &&
-       !audio_->CanAddBuffers(cluster_parser_->audio_buffers())) ||
-      (video_.get() &&
-       !video_->CanAddBuffers(cluster_parser_->video_buffers()))) {
-    return -1;
-  }
+  if (!cluster_parser_->audio_buffers().empty() ||
+      !cluster_parser_->video_buffers().empty()) {
+    // Make sure we can add the buffers to both streams before we actually
+    // add them. This allows us to accept all of the data or none of it.
+    if ((audio_.get() &&
+         !audio_->CanAddBuffers(cluster_parser_->audio_buffers())) ||
+        (video_.get() &&
+         !video_->CanAddBuffers(cluster_parser_->video_buffers()))) {
+      return -1;
+    }
 
-  if (audio_.get())
-    audio_->AddBuffers(cluster_parser_->audio_buffers());
+    if (audio_.get())
+      audio_->AddBuffers(cluster_parser_->audio_buffers());
 
-  if (video_.get())
-    video_->AddBuffers(cluster_parser_->video_buffers());
+    if (video_.get())
+      video_->AddBuffers(cluster_parser_->video_buffers());
+
+    *buffers_added = true;
+  }
 
   // TODO(acolwell) : make this more representative of what is actually
   // buffered.
diff --git a/media/filters/chunk_demuxer.h b/media/filters/chunk_demuxer.h
index b0f0d02..42f1097 100644
--- a/media/filters/chunk_demuxer.h
+++ b/media/filters/chunk_demuxer.h
@@ -81,13 +81,18 @@ class MEDIA_EXPORT ChunkDemuxer : public Demuxer {
   // found.
   bool SetupStreams();
 
-  // Parse a cluster add add the buffers to the appropriate DemxuerStream.
-  // |data| is expected to point to the beginning of a cluster element.
+  // Parse a cluster and add the buffers to the appropriate DemuxerStream. This
+  // method also skips over CUES elements if it happens to encounter them.
+  //
+  // |data| is expected to point to the beginning of an element.
+  //
+  // |buffers_added| - Indicates whether Buffers were added to DemuxerStreams
+  //   during the call. This is only valid if the return value > 0.
   //
   // Returns -1 if the parse fails.
   // Returns 0 if more data is needed.
   // Returns the number of bytes parsed on success.
-  int ParseCluster_Locked(const uint8* data, int size);
+  int ParseCluster_Locked(const uint8* data, int size, bool* buffers_added);
 
   // Reports an error and puts the demuxer in a state where it won't accept more
   // data.
diff --git a/media/media.gyp b/media/media.gyp
index a52d4a5..abe8310 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -621,6 +621,7 @@
         'video/capture/video_capture_device_unittest.cc',
         'webm/cluster_builder.cc',
         'webm/cluster_builder.h',
+        'webm/webm_parser_unittest.cc',
       ],
       'conditions': [
         ['os_posix==1 and OS!="mac"', {
diff --git a/media/webm/webm_cluster_parser.cc b/media/webm/webm_cluster_parser.cc
index 8eb045c..fd716b2 100644
--- a/media/webm/webm_cluster_parser.cc
+++ b/media/webm/webm_cluster_parser.cc
@@ -26,6 +26,7 @@ WebMClusterParser::WebMClusterParser(int64 timecode_scale,
       audio_default_duration_(audio_default_duration),
       video_track_num_(video_track_num),
       video_default_duration_(video_default_duration),
+      parser_(kWebMIdCluster),
       last_block_timecode_(-1),
       cluster_timecode_(-1) {
 }
@@ -33,12 +34,25 @@ WebMClusterParser::WebMClusterParser(int64 timecode_scale,
 WebMClusterParser::~WebMClusterParser() {}
 
 int WebMClusterParser::Parse(const uint8* buf, int size) {
-  last_block_timecode_ = -1;
-  cluster_timecode_ = -1;
   audio_buffers_.clear();
   video_buffers_.clear();
 
-  return WebMParseListElement(buf, size, kWebMIdCluster, 1, this);
+  int result = parser_.Parse(buf, size, this);
+
+  if (result <= 0)
+    return result;
+
+  if (parser_.IsParsingComplete()) {
+    // Reset the parser if we're done parsing so that
+    // it is ready to accept another cluster on the next
+    // call.
+    parser_.Reset();
+
+    last_block_timecode_ = -1;
+    cluster_timecode_ = -1;
+  }
+
+  return result;
 }
 
 bool WebMClusterParser::OnListStart(int id) {
@@ -67,17 +81,17 @@ bool WebMClusterParser::OnUInt(int id, int64 val) {
 }
 
 bool WebMClusterParser::OnFloat(int id, double val) {
-  VLOG(1) << "Unexpected float element with ID " << std::hex << id;
+  DVLOG(1) << "Unexpected float element with ID " << std::hex << id;
   return false;
 }
 
 bool WebMClusterParser::OnBinary(int id, const uint8* data, int size) {
-  VLOG(1) << "Unexpected binary element with ID " << std::hex << id;
+  DVLOG(1) << "Unexpected binary element with ID " << std::hex << id;
   return false;
 }
 
 bool WebMClusterParser::OnString(int id, const std::string& str) {
-  VLOG(1) << "Unexpected string element with ID " << std::hex << id;
+  DVLOG(1) << "Unexpected string element with ID " << std::hex << id;
   return false;
 }
 
@@ -85,17 +99,17 @@ bool WebMClusterParser::OnSimpleBlock(int track_num, int timecode,
                                       int flags,
                                       const uint8* data, int size) {
   if (cluster_timecode_ == -1) {
-    VLOG(1) << "Got SimpleBlock before cluster timecode.";
+    DVLOG(1) << "Got SimpleBlock before cluster timecode.";
     return false;
   }
 
   if (timecode < 0) {
-    VLOG(1) << "Got SimpleBlock with negative timecode offset " << timecode;
+    DVLOG(1) << "Got SimpleBlock with negative timecode offset " << timecode;
     return false;
   }
 
   if (last_block_timecode_ != -1 && timecode < last_block_timecode_) {
-    VLOG(1) << "Got SimpleBlock with a timecode before the previous block.";
+    DVLOG(1) << "Got SimpleBlock with a timecode before the previous block.";
     return false;
   }
 
@@ -115,13 +129,13 @@ bool WebMClusterParser::OnSimpleBlock(int track_num, int timecode,
     buffer->SetDuration(video_default_duration_);
     queue = &video_buffers_;
   } else {
-    VLOG(1) << "Unexpected track number " << track_num;
+    DVLOG(1) << "Unexpected track number " << track_num;
     return false;
   }
 
   if (!queue->empty() &&
       buffer->GetTimestamp() == queue->back()->GetTimestamp()) {
-    VLOG(1) << "Got SimpleBlock timecode is not strictly monotonically "
+    DVLOG(1) << "Got SimpleBlock timecode is not strictly monotonically "
             << "increasing for track " << track_num;
     return false;
   }
diff --git a/media/webm/webm_cluster_parser.h b/media/webm/webm_cluster_parser.h
index 5a367b0..7fb1b94 100644
--- a/media/webm/webm_cluster_parser.h
+++ b/media/webm/webm_cluster_parser.h
@@ -53,6 +53,8 @@ class WebMClusterParser : public WebMParserClient {
   int video_track_num_;
   base::TimeDelta  video_default_duration_;
 
+  WebMListParser parser_;
+
   int64 last_block_timecode_;
 
   int64 cluster_timecode_;
diff --git a/media/webm/webm_constants.h b/media/webm/webm_constants.h
index 471115b..96e7c01 100644
--- a/media/webm/webm_constants.h
+++ b/media/webm/webm_constants.h
@@ -64,6 +64,8 @@ const int kWebMIdVideo = 0xE0;
 const int kWebMIdVoid = 0xEC;
 const int kWebMIdWritingApp = 0x5741;
 
+const int64 kWebMUnknownSize = GG_LONGLONG(0x00FFFFFFFFFFFFFF);
+
 // Default timecode scale if the TimecodeScale element is
 // not specified in the INFO element.
 const int kWebMDefaultTimecodeScale = 1000000;
diff --git a/media/webm/webm_info_parser.cc b/media/webm/webm_info_parser.cc
index 41e1a25..5807d7e 100644
--- a/media/webm/webm_info_parser.cc
+++ b/media/webm/webm_info_parser.cc
@@ -17,7 +17,17 @@ WebMInfoParser::WebMInfoParser()
 WebMInfoParser::~WebMInfoParser() {}
 
 int WebMInfoParser::Parse(const uint8* buf, int size) {
-  return WebMParseListElement(buf, size, kWebMIdInfo, 1, this);
+  timecode_scale_ = -1;
+  duration_ = -1;
+
+  WebMListParser parser(kWebMIdInfo);
+  int result = parser.Parse(buf, size, this);
+
+  if (result <= 0)
+    return result;
+
+  // For now we do all or nothing parsing.
+  return parser.IsParsingComplete() ? result : 0;
 }
 
 bool WebMInfoParser::OnListStart(int id) { return true; }
@@ -36,7 +46,7 @@ bool WebMInfoParser::OnUInt(int id, int64 val) {
     return true;
 
   if (timecode_scale_ != -1) {
-    VLOG(1) << "Multiple values for id " << std::hex << id << " specified";
+    DVLOG(1) << "Multiple values for id " << std::hex << id << " specified";
     return false;
   }
 
@@ -46,12 +56,12 @@ bool WebMInfoParser::OnUInt(int id, int64 val) {
 
 bool WebMInfoParser::OnFloat(int id, double val) {
   if (id != kWebMIdDuration) {
-    VLOG(1) << "Unexpected float for id" << std::hex << id;
+    DVLOG(1) << "Unexpected float for id" << std::hex << id;
     return false;
   }
 
   if (duration_ != -1) {
-    VLOG(1) << "Multiple values for duration.";
+    DVLOG(1) << "Multiple values for duration.";
     return false;
   }
 
diff --git a/media/webm/webm_parser.cc b/media/webm/webm_parser.cc
index 1e42815..1422308 100644
--- a/media/webm/webm_parser.cc
+++ b/media/webm/webm_parser.cc
@@ -20,6 +20,7 @@ namespace media {
 static const int kMaxLevelDepth = 6;
 
 enum ElementType {
+  UNKNOWN,
   LIST,
   UINT,
   FLOAT,
@@ -30,13 +31,13 @@ enum ElementType {
 };
 
 struct ElementIdInfo {
-  int level_;
   ElementType type_;
   int id_;
 };
 
 struct ListElementInfo {
   int id_;
+  int level_;
   const ElementIdInfo* id_info_;
   int id_info_size_;
 };
@@ -47,84 +48,83 @@ struct ListElementInfo {
 // marked as SKIP because they are valid, but we don't care about them
 // right now.
 static const ElementIdInfo kClusterIds[] = {
-  {2, UINT, kWebMIdTimecode},
-  {2, SBLOCK, kWebMIdSimpleBlock},
-  {2, LIST, kWebMIdBlockGroup},
+  {UINT, kWebMIdTimecode},
+  {SBLOCK, kWebMIdSimpleBlock},
+  {LIST, kWebMIdBlockGroup},
+};
+
+static const ElementIdInfo kSegmentIds[] = {
+  {SKIP, kWebMIdSeekHead},  // TODO(acolwell): add SeekHead info
+  {LIST, kWebMIdInfo},
+  {LIST, kWebMIdCluster},
+  {LIST, kWebMIdTracks},
+  {SKIP, kWebMIdCues},  // TODO(acolwell): add CUES info
 };
 
 static const ElementIdInfo kInfoIds[] = {
-  {2, SKIP, kWebMIdSegmentUID},
-  {2, UINT, kWebMIdTimecodeScale},
-  {2, FLOAT, kWebMIdDuration},
-  {2, SKIP, kWebMIdDateUTC},
-  {2, SKIP, kWebMIdTitle},
-  {2, SKIP, kWebMIdMuxingApp},
-  {2, SKIP, kWebMIdWritingApp},
+  {SKIP, kWebMIdSegmentUID},
+  {UINT, kWebMIdTimecodeScale},
+  {FLOAT, kWebMIdDuration},
+  {SKIP, kWebMIdDateUTC},
+  {SKIP, kWebMIdTitle},
+  {SKIP, kWebMIdMuxingApp},
+  {SKIP, kWebMIdWritingApp},
 };
 
 static const ElementIdInfo kTracksIds[] = {
-  {2, LIST, kWebMIdTrackEntry},
+  {LIST, kWebMIdTrackEntry},
 };
 
 static const ElementIdInfo kTrackEntryIds[] = {
-  {3, UINT, kWebMIdTrackNumber},
-  {3, SKIP, kWebMIdTrackUID},
-  {3, UINT, kWebMIdTrackType},
-  {3, SKIP, kWebMIdFlagEnabled},
-  {3, SKIP, kWebMIdFlagDefault},
-  {3, SKIP, kWebMIdFlagForced},
-  {3, UINT, kWebMIdFlagLacing},
-  {3, UINT, kWebMIdDefaultDuration},
-  {3, SKIP, kWebMIdName},
-  {3, SKIP, kWebMIdLanguage},
-  {3, STRING, kWebMIdCodecID},
-  {3, BINARY, kWebMIdCodecPrivate},
-  {3, SKIP, kWebMIdCodecName},
-  {3, LIST, kWebMIdVideo},
-  {3, LIST, kWebMIdAudio},
+  {UINT, kWebMIdTrackNumber},
+  {SKIP, kWebMIdTrackUID},
+  {UINT, kWebMIdTrackType},
+  {SKIP, kWebMIdFlagEnabled},
+  {SKIP, kWebMIdFlagDefault},
+  {SKIP, kWebMIdFlagForced},
+  {UINT, kWebMIdFlagLacing},
+  {UINT, kWebMIdDefaultDuration},
+  {SKIP, kWebMIdName},
+  {SKIP, kWebMIdLanguage},
+  {STRING, kWebMIdCodecID},
+  {BINARY, kWebMIdCodecPrivate},
+  {SKIP, kWebMIdCodecName},
+  {LIST, kWebMIdVideo},
+  {LIST, kWebMIdAudio},
 };
 
 static const ElementIdInfo kVideoIds[] = {
-  {4, SKIP, kWebMIdFlagInterlaced},
-  {4, SKIP, kWebMIdStereoMode},
-  {4, UINT, kWebMIdPixelWidth},
-  {4, UINT, kWebMIdPixelHeight},
-  {4, SKIP, kWebMIdPixelCropBottom},
-  {4, SKIP, kWebMIdPixelCropTop},
-  {4, SKIP, kWebMIdPixelCropLeft},
-  {4, SKIP, kWebMIdPixelCropRight},
-  {4, SKIP, kWebMIdDisplayWidth},
-  {4, SKIP, kWebMIdDisplayHeight},
-  {4, SKIP, kWebMIdDisplayUnit},
-  {4, SKIP, kWebMIdAspectRatioType},
+  {SKIP, kWebMIdFlagInterlaced},
+  {SKIP, kWebMIdStereoMode},
+  {UINT, kWebMIdPixelWidth},
+  {UINT, kWebMIdPixelHeight},
+  {SKIP, kWebMIdPixelCropBottom},
+  {SKIP, kWebMIdPixelCropTop},
+  {SKIP, kWebMIdPixelCropLeft},
+  {SKIP, kWebMIdPixelCropRight},
+  {SKIP, kWebMIdDisplayWidth},
+  {SKIP, kWebMIdDisplayHeight},
+  {SKIP, kWebMIdDisplayUnit},
+  {SKIP, kWebMIdAspectRatioType},
 };
 
 static const ElementIdInfo kAudioIds[] = {
-  {4, SKIP, kWebMIdSamplingFrequency},
-  {4, SKIP, kWebMIdOutputSamplingFrequency},
-  {4, UINT, kWebMIdChannels},
-  {4, SKIP, kWebMIdBitDepth},
-};
-
-static const ElementIdInfo kClustersOnly[] = {
-  {1, LIST, kWebMIdCluster},
+  {SKIP, kWebMIdSamplingFrequency},
+  {SKIP, kWebMIdOutputSamplingFrequency},
+  {UINT, kWebMIdChannels},
+  {SKIP, kWebMIdBitDepth},
 };
 
 static const ListElementInfo kListElementInfo[] = {
-  { kWebMIdCluster,    kClusterIds,    sizeof(kClusterIds) },
-  { kWebMIdInfo,       kInfoIds,       sizeof(kInfoIds) },
-  { kWebMIdTracks,     kTracksIds,     sizeof(kTracksIds) },
-  { kWebMIdTrackEntry, kTrackEntryIds, sizeof(kTrackEntryIds) },
-  { kWebMIdVideo,      kVideoIds,      sizeof(kVideoIds) },
-  { kWebMIdAudio,      kAudioIds,      sizeof(kAudioIds) },
+  { kWebMIdCluster,    1, kClusterIds,    sizeof(kClusterIds) },
+  { kWebMIdSegment,    0, kSegmentIds,    sizeof(kSegmentIds) },
+  { kWebMIdInfo,       1, kInfoIds,       sizeof(kInfoIds) },
+  { kWebMIdTracks,     1, kTracksIds,     sizeof(kTracksIds) },
+  { kWebMIdTrackEntry, 2, kTrackEntryIds, sizeof(kTrackEntryIds) },
+  { kWebMIdVideo,      3, kVideoIds,      sizeof(kVideoIds) },
+  { kWebMIdAudio,      3, kAudioIds,      sizeof(kAudioIds) },
 };
 
-// Number of elements in kListElementInfo.
-const int kListElementInfoCount =
-    sizeof(kListElementInfo) / sizeof(ListElementInfo);
-
-WebMParserClient::~WebMParserClient() {}
-
 // Parses an element header id or size field. These fields are variable length
 // encoded. The first byte indicates how many bytes the field occupies.
 // |buf|  - The buffer to parse.
@@ -206,22 +206,27 @@ int WebMParseElementHeader(const uint8* buf, int size,
   return num_id_bytes + num_size_bytes;
 }
 
-// Finds ElementIdInfo for a specific ID.
-static const ElementIdInfo* FindIdInfo(int id,
-                                       const ElementIdInfo* id_info,
-                                       int id_info_size) {
+// Finds ElementType for a specific ID.
+static ElementType FindIdType(int id,
+                              const ElementIdInfo* id_info,
+                              int id_info_size) {
+
+  // Check for global element IDs that can be anywhere.
+  if (id == kWebMIdVoid || id == kWebMIdCRC32)
+    return SKIP;
+
   int count = id_info_size / sizeof(*id_info);
   for (int i = 0; i < count; ++i) {
     if (id == id_info[i].id_)
-      return &id_info[i];
+      return id_info[i].type_;
   }
 
-  return NULL;
+  return UNKNOWN;
 }
 
 // Finds ListElementInfo for a specific ID.
 static const ListElementInfo* FindListInfo(int id) {
-  for (int i = 0; i < kListElementInfoCount; ++i) {
+  for (size_t i = 0; i < arraysize(kListElementInfo); ++i) {
     if (id == kListElementInfo[i].id_)
       return &kListElementInfo[i];
   }
@@ -237,7 +242,7 @@ static int ParseSimpleBlock(const uint8* buf, int size,
   // Return an error if the trackNum > 127. We just aren't
   // going to support large track numbers right now.
   if ((buf[0] & 0x80) != 0x80) {
-    VLOG(1) << "TrackNumber over 127 not supported";
+    DVLOG(1) << "TrackNumber over 127 not supported";
     return -1;
   }
 
@@ -247,7 +252,7 @@ static int ParseSimpleBlock(const uint8* buf, int size,
   int lacing = (flags >> 1) & 0x3;
 
   if (lacing != 0) {
-    VLOG(1) << "Lacing " << lacing << " not supported yet.";
+    DVLOG(1) << "Lacing " << lacing << " not supported yet.";
     return -1;
   }
 
@@ -265,39 +270,6 @@ static int ParseSimpleBlock(const uint8* buf, int size,
   return size;
 }
 
-static int ParseElements(const ElementIdInfo* id_info,
-                         int id_info_size,
-                         const uint8* buf, int size, int level,
-                         WebMParserClient* client);
-
-static int ParseElementList(const uint8* buf, int size,
-                            int id, int level,
-                            WebMParserClient* client) {
-  const ListElementInfo* list_info = FindListInfo(id);
-
-  if (!list_info) {
-    VLOG(1) << "Failed to find list info for ID " << std::hex << id;
-    return -1;
-  }
-
-  if (!client->OnListStart(id))
-    return -1;
-
-  int result = ParseElements(list_info->id_info_,
-                             list_info->id_info_size_,
-                             buf, size,
-                             level + 1,
-                             client);
-
-  if (result <= 0)
-    return result;
-
-  if (!client->OnListEnd(id))
-    return -1;
-
-  DCHECK_EQ(result, size);
-  return result;
-}
 
 static int ParseUInt(const uint8* buf, int size, int id,
                      WebMParserClient* client) {
@@ -354,142 +326,285 @@ static int ParseFloat(const uint8* buf, int size, int id,
   return size;
 }
 
-static int ParseElements(const ElementIdInfo* id_info,
-                         int id_info_size,
-                         const uint8* buf, int size, int level,
-                         WebMParserClient* client) {
-  DCHECK_GE(id_info_size, 0);
-  DCHECK_GE(size, 0);
-  DCHECK_GE(level, 0);
+static int ParseNonListElement(ElementType type, int id, int64 element_size,
+                               const uint8* buf, int size,
+                               WebMParserClient* client) {
+  DCHECK_GE(size, element_size);
 
-  const uint8* cur = buf;
-  int cur_size = size;
-  int used = 0;
+  int result = -1;
+  switch(type) {
+    case SBLOCK:
+      result = ParseSimpleBlock(buf, element_size, client);
+      break;
+    case LIST:
+      NOTIMPLEMENTED();
+      result = -1;
+      break;
+    case UINT:
+      result = ParseUInt(buf, element_size, id, client);
+      break;
+    case FLOAT:
+      result = ParseFloat(buf, element_size, id, client);
+      break;
+    case BINARY:
+      if (client->OnBinary(id, buf, element_size)) {
+        result = element_size;
+      } else {
+        result = -1;
+      }
+      break;
+    case STRING:
+      if (client->OnString(id,
+                           std::string(reinterpret_cast<const char*>(buf),
+                                       element_size))) {
+        result = element_size;
+      } else {
+        result = -1;
+      }
+      break;
+    case SKIP:
+      result = element_size;
+      break;
+    default:
+      DVLOG(1) << "Unhandled ID type " << type;
+      return -1;
+  };
 
-  if (level > kMaxLevelDepth)
-    return -1;
+  DCHECK_LE(result, size);
+  return result;
+}
 
-  while (cur_size > 0) {
-    int id = 0;
-    int64 element_size = 0;
-    int result = WebMParseElementHeader(cur, cur_size, &id, &element_size);
+WebMParserClient::WebMParserClient() {}
+WebMParserClient::~WebMParserClient() {}
 
-    if (result <= 0)
-      return result;
+WebMListParser::WebMListParser(int id)
+    : state_(NEED_LIST_HEADER),
+      root_id_(id) {
+  const ListElementInfo* list_info = FindListInfo(id);
 
-    cur += result;
-    cur_size -= result;
-    used += result;
+  DCHECK(list_info);
 
-    // Check to see if the element is larger than the remaining data.
-    if (element_size > cur_size)
-      return 0;
+  root_level_ = list_info->level_;
+}
 
-    const ElementIdInfo* info = FindIdInfo(id, id_info, id_info_size);
+WebMListParser::~WebMListParser() {}
 
-    if (info == NULL) {
-      VLOG(1) << "No info for ID " << std::hex << id;
+void WebMListParser::Reset() {
+  ChangeState(NEED_LIST_HEADER);
+  list_state_stack_.clear();
+}
 
-      // TODO(acolwell): Change this to return -1 after the API has solidified.
-      // We don't want to allow elements we don't recognize.
-      cur += element_size;
-      cur_size -= element_size;
-      used += element_size;
-      continue;
-    }
+int WebMListParser::Parse(const uint8* buf, int size,
+                          WebMParserClient* client) {
+  DCHECK(buf);
+  DCHECK(client);
 
-    if (info->level_ != level) {
-      VLOG(1) << "ID " << std::hex << id << std::dec << " at level "
-              << level << " instead of " << info->level_;
-      return -1;
-    }
+  if (size < 0 || state_ == PARSE_ERROR || state_ == DONE_PARSING_LIST)
+    return -1;
 
-    switch(info->type_) {
-      case SBLOCK:
-        if (ParseSimpleBlock(cur, element_size, client) <= 0)
-          return -1;
-        break;
-      case LIST:
-        if (ParseElementList(cur, element_size, id, level, client) < 0)
-          return -1;
-        break;
-      case UINT:
-        if (ParseUInt(cur, element_size, id, client) <= 0)
+  if (size == 0)
+    return 0;
+
+  const uint8* cur = buf;
+  int cur_size = size;
+  int bytes_parsed = 0;
+
+  while (cur_size > 0 && state_ != PARSE_ERROR && state_ != DONE_PARSING_LIST) {
+    int element_id = 0;
+    int64 element_size = 0;
+    int result = WebMParseElementHeader(cur, cur_size, &element_id,
+                                        &element_size);
+
+    if (result < 0)
+      return result;
+
+    if (result == 0)
+      return bytes_parsed;
+
+    switch(state_) {
+      case NEED_LIST_HEADER: {
+        if (element_id != root_id_) {
+          ChangeState(PARSE_ERROR);
           return -1;
-        break;
-      case FLOAT:
-        if (ParseFloat(cur, element_size, id, client) <= 0)
+        }
+
+        // TODO(acolwell): Add support for lists of unknown size.
+        if (element_size == kWebMUnknownSize) {
+          ChangeState(PARSE_ERROR);
           return -1;
-        break;
-      case BINARY:
-        if (!client->OnBinary(id, cur, element_size))
+        }
+
+        ChangeState(INSIDE_LIST);
+        if (!OnListStart(root_id_, element_size, client))
           return -1;
+
         break;
-      case STRING:
-        if (!client->OnString(id,
-                              std::string(reinterpret_cast<const char*>(cur),
-                                          element_size)))
+      }
+
+      case INSIDE_LIST: {
+        int header_size = result;
+        const uint8* element_data = cur + header_size;
+        int element_data_size = cur_size - header_size;
+
+        if (element_size < element_data_size)
+          element_data_size = element_size;
+
+        result = ParseListElement(header_size, element_id, element_size,
+                                  element_data, element_data_size, client);
+
+        DCHECK_LE(result, header_size + element_data_size);
+        if (result < 0) {
+          ChangeState(PARSE_ERROR);
           return -1;
+        }
+
+        if (result == 0)
+          return bytes_parsed;
+
         break;
-      case SKIP:
-        // Do nothing.
+      }
+      case DONE_PARSING_LIST:
+      case PARSE_ERROR:
+        // Shouldn't be able to get here.
+        NOTIMPLEMENTED();
         break;
-      default:
-        VLOG(1) << "Unhandled id type " << info->type_;
-        return -1;
-    };
-
-    cur += element_size;
-    cur_size -= element_size;
-    used += element_size;
+    }
+
+    cur += result;
+    cur_size -= result;
+    bytes_parsed += result;
   }
 
-  return used;
+  return (state_ == PARSE_ERROR) ? -1 : bytes_parsed;
 }
 
-// Parses a single list element that matches |id|. This method fails if the
-// buffer points to an element that does not match |id|.
-int WebMParseListElement(const uint8* buf, int size, int id,
-                         int level, WebMParserClient* client) {
-  if (size < 0)
-    return -1;
+bool WebMListParser::IsParsingComplete() const {
+  return state_ == DONE_PARSING_LIST;
+}
 
-  if (size == 0)
-    return 0;
+void WebMListParser::ChangeState(State new_state) {
+  state_ = new_state;
+}
 
-  const uint8* cur = buf;
-  int cur_size = size;
-  int bytes_parsed = 0;
-  int element_id = 0;
-  int64 element_size = 0;
-  int result = WebMParseElementHeader(cur, cur_size, &element_id,
-                                      &element_size);
+int WebMListParser::ParseListElement(int header_size,
+                                     int id, int64 element_size,
+                                     const uint8* data, int size,
+                                     WebMParserClient* client) {
+  DCHECK_GT(list_state_stack_.size(), 0u);
 
-  if (result <= 0)
-    return result;
+  ListState& list_state = list_state_stack_.back();
+  DCHECK(list_state.element_info_);
 
-  cur += result;
-  cur_size -= result;
-  bytes_parsed += result;
+  const ListElementInfo* element_info = list_state.element_info_;
+  ElementType id_type =
+      FindIdType(id, element_info->id_info_, element_info->id_info_size_);
+
+  // Unexpected ID.
+  if (id_type == UNKNOWN) {
+    DVLOG(1) << "No ElementType info for ID 0x" << std::hex << id;
+    return -1;
+  }
 
-  if (element_id != id)
+  // Make sure the whole element can fit inside the current list.
+  int64 total_element_size = header_size + element_size;
+  if (list_state.size_ != kWebMUnknownSize &&
+      list_state.size_ < list_state.bytes_parsed_ + total_element_size) {
     return -1;
+  }
+
+  if (id_type == LIST) {
+    list_state.bytes_parsed_ += header_size;
+
+    if (!OnListStart(id, element_size, client))
+      return -1;
+    return header_size;
+  }
 
-  if (element_size > cur_size)
+  // Make sure we have the entire element before trying to parse a non-list
+  // element.
+  if (size < element_size)
     return 0;
 
-  if (element_size > 0) {
-    result = ParseElementList(cur, element_size, element_id, level, client);
+  int bytes_parsed = ParseNonListElement(id_type, id, element_size,
+                                         data, size, client);
+  DCHECK_LE(bytes_parsed, size);
 
-    if (result <= 0)
-      return result;
+  // Return if an error occurred or we need more data.
+  // Note: bytes_parsed is 0 for a successful parse of a size 0 element. We
+  // need to check the element_size to disambiguate the "need more data" case
+  // from a successful parse.
+  if (bytes_parsed < 0 || (bytes_parsed == 0 && element_size != 0))
+    return bytes_parsed;
 
-    cur += result;
-    cur_size -= result;
-    bytes_parsed += result;
+  int result = header_size + bytes_parsed;
+  list_state.bytes_parsed_ += result;
+
+  // See if we have reached the end of the current list.
+  if (list_state.bytes_parsed_ == list_state.size_) {
+    if (!OnListEnd(client))
+      return -1;
+  }
+
+  return result;
+}
+
+bool WebMListParser::OnListStart(int id, int64 size, WebMParserClient* client) {
+  ListState list_state = { id, size, 0, FindListInfo(id)};
+
+  if (!list_state.element_info_)
+    return false;
+
+  int current_level = root_level_ + list_state_stack_.size() - 1;
+  if (current_level + 1 != list_state.element_info_->level_)
+    return false;
+
+  if (!list_state_stack_.empty()) {
+
+    // Make sure the new list doesn't go past the end of the current list.
+    ListState current_list = list_state_stack_.back();
+    if (current_list.size_ != kWebMUnknownSize &&
+        current_list.size_ < current_list.bytes_parsed_ + size)
+      return false;
   }
 
-  return bytes_parsed;
+  if (!client->OnListStart(id))
+    return false;
+
+  list_state_stack_.push_back(list_state);
+
+  if (size == 0) {
+    return OnListEnd(client);
+  }
+
+  return true;
+}
+
+bool WebMListParser::OnListEnd(WebMParserClient* client) {
+  int lists_ended = 0;
+  for (; !list_state_stack_.empty(); ++lists_ended) {
+    const ListState& list_state = list_state_stack_.back();
+
+    if (list_state.bytes_parsed_ != list_state.size_)
+      break;
+
+    if (!client->OnListEnd(list_state.id_))
+      return false;
+
+    int64 bytes_parsed = list_state.bytes_parsed_;
+    list_state_stack_.pop_back();
+
+    if (!list_state_stack_.empty()) {
+      // Update the bytes_parsed_ for the parent element.
+      list_state_stack_.back().bytes_parsed_ += bytes_parsed;
+    }
+  }
+
+  DCHECK_GE(lists_ended, 1);
+
+  if (list_state_stack_.empty())
+    ChangeState(DONE_PARSING_LIST);
+
+  return true;
 }
 
 }  // namespace media
diff --git a/media/webm/webm_parser.h b/media/webm/webm_parser.h
index 7d15f9b..bc3e09f 100644
--- a/media/webm/webm_parser.h
+++ b/media/webm/webm_parser.h
@@ -6,8 +6,10 @@
 #define MEDIA_WEBM_WEBM_PARSER_H_
 
 #include <string>
+#include <vector>
 
 #include "base/basictypes.h"
+#include "media/base/media_export.h"
 
 namespace media {
 
@@ -21,7 +23,7 @@ namespace media {
 // indicates whether the parsed data is valid. If false is returned
 // then the parse is immediately terminated and an error is reported by the
 // parser.
-class WebMParserClient {
+class MEDIA_EXPORT WebMParserClient {
  public:
   virtual ~WebMParserClient();
 
@@ -34,6 +36,106 @@ class WebMParserClient {
   virtual bool OnSimpleBlock(int track_num, int timecode,
                              int flags,
                              const uint8* data, int size) = 0;
+ protected:
+  WebMParserClient();
+
+  DISALLOW_COPY_AND_ASSIGN(WebMParserClient);
+};
+
+struct ListElementInfo;
+
+// Parses a WebM list element and all of its children. This
+// class supports incremental parsing of the list so Parse()
+// can be called multiple times with pieces of the list.
+// IsParsingComplete() will return true once the entire list has
+// been parsed.
+class MEDIA_EXPORT WebMListParser {
+ public:
+  // |id| - Element ID of the list we intend to parse.
+  explicit WebMListParser(int id);
+  ~WebMListParser();
+
+  // Resets the state of the parser so it can start parsing a new list.
+  void Reset();
+
+  // Parses list data contained in |buf|.
+  // |client| Called as different elements in the list are parsed.
+  //
+  // Returns < 0 if the parse fails.
+  // Returns 0 if more data is needed.
+  // Returning > 0 indicates success & the number of bytes parsed.
+  int Parse(const uint8* buf, int size, WebMParserClient* client);
+
+  // Returns true if the entire list has been parsed.
+  bool IsParsingComplete() const;
+
+ private:
+  enum State {
+    NEED_LIST_HEADER,
+    INSIDE_LIST,
+    DONE_PARSING_LIST,
+    PARSE_ERROR,
+  };
+
+  struct ListState {
+    int id_;
+    int size_;
+    int bytes_parsed_;
+    const ListElementInfo* element_info_;
+  };
+
+  void ChangeState(State new_state);
+
+  // Parses a single element in the current list.
+  //
+  // |header_size| - The size of the element header
+  // |id| - The ID of the element being parsed.
+  // |element_size| - The size of the element body.
+  // |data| - Pointer to the element contents.
+  // |size| - Number of bytes in |data|
+  // |client| - Client to pass the parsed data to.
+  //
+  // Returns < 0 if the parse fails.
+  // Returns 0 if more data is needed.
+  // Returning > 0 indicates success & the number of bytes parsed.
+  int ParseListElement(int header_size,
+                       int id, int64 element_size,
+                       const uint8* data, int size,
+                       WebMParserClient* client);
+
+  // Called when starting to parse a new list.
+  //
+  // |id| - The ID of the new list.
+  // |size| - The size of the new list.
+  // |client| - The client object to notify that a new list is being parsed.
+  //
+  // Returns true if this list can be started in the current context. False
+  // if starting this list causes some sort of parse error.
+  bool OnListStart(int id, int64 size, WebMParserClient* client);
+
+  // Called when the end of the current list has been reached. This may also
+  // signal the end of the current list's ancestors if the current list happens
+  // to be at the end of its parent.
+  //
+  // |client| - The client to notify about lists ending.
+  //
+  // Returns true if no errors occurred while ending this list(s).
+  bool OnListEnd(WebMParserClient* client);
+
+  State state_;
+
+  // Element ID passed to the constructor.
+  int root_id_;
+
+  // Element level for |root_id_|. Used to verify that elements appear at
+  // the correct level.
+  int root_level_;
+
+  // Stack of state for all the lists currently being parsed. Lists are
+  // added and removed from this stack as they are parsed.
+  std::vector<ListState> list_state_stack_;
+
+  DISALLOW_COPY_AND_ASSIGN(WebMListParser);
 };
 
 // Parses an element header & returns the ID and element size.
@@ -47,15 +149,6 @@ class WebMParserClient {
 int WebMParseElementHeader(const uint8* buf, int size,
                            int* id, int64* element_size);
 
-// Parses a single list element that matches |id|. This method fails if the
-// buffer points to an element that does not match |id|.
-//
-// Returns -1 if the parse fails.
-// Returns 0 if more data is needed.
-// Returns the number of bytes parsed on success.
-int WebMParseListElement(const uint8* buf, int size, int id,
-                         int level, WebMParserClient* client);
-
 }  // namespace media
 
 #endif  // MEDIA_WEBM_WEBM_PARSER_H_
diff --git a/media/webm/webm_parser_unittest.cc b/media/webm/webm_parser_unittest.cc
new file mode 100644
index 0000000..e377fda
--- /dev/null
+++ b/media/webm/webm_parser_unittest.cc
@@ -0,0 +1,264 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/webm/cluster_builder.h"
+#include "media/webm/webm_constants.h"
+#include "media/webm/webm_parser.h"
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+using ::testing::InSequence;
+using ::testing::Return;
+using ::testing::StrictMock;
+using ::testing::_;
+
+namespace media {
+
+class MockWebMParserClient : public WebMParserClient {
+ public:
+  virtual ~MockWebMParserClient() {}
+
+  // WebMParserClient methods.
+  MOCK_METHOD1(OnListStart, bool(int));
+  MOCK_METHOD1(OnListEnd, bool(int));
+  MOCK_METHOD2(OnUInt, bool(int, int64));
+  MOCK_METHOD2(OnFloat, bool(int, double));
+  MOCK_METHOD3(OnBinary, bool(int, const uint8*, int));
+  MOCK_METHOD2(OnString, bool(int, const std::string&));
+  MOCK_METHOD5(OnSimpleBlock, bool(int, int, int, const uint8*, int));
+};
+
+class WebMParserTest : public testing::Test {
+ protected:
+  StrictMock<MockWebMParserClient> client_;
+};
+
+struct SimpleBlockInfo {
+  int track_num;
+  int timestamp;
+};
+
+static void AddSimpleBlock(ClusterBuilder* cb, int track_num,
+                           int64 timecode) {
+  uint8 data[] = { 0x00 };
+  cb->AddSimpleBlock(track_num, timecode, 0, data, sizeof(data));
+}
+
+static Cluster* CreateCluster(int timecode,
+                              const SimpleBlockInfo* block_info,
+                              int block_count) {
+  ClusterBuilder cb;
+  cb.SetClusterTimecode(0);
+
+  for (int i = 0; i < block_count; i++)
+    AddSimpleBlock(&cb, block_info[i].track_num, block_info[i].timestamp);
+
+  return cb.Finish();
+}
+
+static void CreateClusterExpectations(int timecode,
+                                      const SimpleBlockInfo* block_info,
+                                      int block_count,
+                                      MockWebMParserClient* client) {
+
+  InSequence s;
+  EXPECT_CALL(*client, OnListStart(kWebMIdCluster)).WillOnce(Return(true));
+  EXPECT_CALL(*client, OnUInt(kWebMIdTimecode, 0)).WillOnce(Return(true));
+
+  for (int i = 0; i < block_count; i++) {
+    EXPECT_CALL(*client, OnSimpleBlock(block_info[i].track_num,
+                                       block_info[i].timestamp,
+                                       _, _, _))
+        .WillOnce(Return(true));
+  }
+
+  EXPECT_CALL(*client, OnListEnd(kWebMIdCluster)).WillOnce(Return(true));
+}
+
+TEST_F(WebMParserTest, EmptyCluster) {
+  const uint8 kEmptyCluster[] = {
+    0x1F, 0x43, 0xB6, 0x75, 0x80  // CLUSTER (size = 0)
+  };
+  int size = sizeof(kEmptyCluster);
+
+  InSequence s;
+  EXPECT_CALL(client_, OnListStart(kWebMIdCluster)).WillOnce(Return(true));
+  EXPECT_CALL(client_, OnListEnd(kWebMIdCluster)).WillOnce(Return(true));
+
+  WebMListParser parser(kWebMIdCluster);
+  int result = parser.Parse(kEmptyCluster, size, &client_);
+  EXPECT_EQ(size, result);
+  EXPECT_TRUE(parser.IsParsingComplete());
+}
+
+TEST_F(WebMParserTest, EmptyClusterInSegment) {
+  const uint8 kBuffer[] = {
+    0x18, 0x53, 0x80, 0x67, 0x85,  // SEGMENT (size = 5)
+    0x1F, 0x43, 0xB6, 0x75, 0x80,  // CLUSTER (size = 0)
+  };
+  int size = sizeof(kBuffer);
+
+  InSequence s;
+  EXPECT_CALL(client_, OnListStart(kWebMIdSegment)).WillOnce(Return(true));
+  EXPECT_CALL(client_, OnListStart(kWebMIdCluster)).WillOnce(Return(true));
+  EXPECT_CALL(client_, OnListEnd(kWebMIdCluster)).WillOnce(Return(true));
+  EXPECT_CALL(client_, OnListEnd(kWebMIdSegment)).WillOnce(Return(true));
+
+  WebMListParser parser(kWebMIdSegment);
+  int result = parser.Parse(kBuffer, size, &client_);
+  EXPECT_EQ(size, result);
+  EXPECT_TRUE(parser.IsParsingComplete());
+}
+
+// Test the case where a non-list child element has a size
+// that is beyond the end of the parent.
+TEST_F(WebMParserTest, ChildNonListLargerThanParent) {
+  const uint8 kBuffer[] = {
+    0x1F, 0x43, 0xB6, 0x75, 0x81,  // CLUSTER (size = 1)
+    0xE7, 0x81, 0x01,  // Timecode (size=1, value=1)
+  };
+  int size = sizeof(kBuffer);
+
+  InSequence s;
+  EXPECT_CALL(client_, OnListStart(kWebMIdCluster)).WillOnce(Return(true));
+
+  WebMListParser parser(kWebMIdCluster);
+  int result = parser.Parse(kBuffer, size, &client_);
+  EXPECT_EQ(-1, result);
+  EXPECT_FALSE(parser.IsParsingComplete());
+}
+
+// Test the case where a list child element has a size
+// that is beyond the end of the parent.
+TEST_F(WebMParserTest, ChildListLargerThanParent) {
+  const uint8 kBuffer[] = {
+    0x18, 0x53, 0x80, 0x67, 0x85,  // SEGMENT (size = 5)
+    0x1F, 0x43, 0xB6, 0x75, 0x81, 0x11  // CLUSTER (size = 1)
+  };
+  int size = sizeof(kBuffer);
+
+  InSequence s;
+  EXPECT_CALL(client_, OnListStart(kWebMIdSegment)).WillOnce(Return(true));
+
+  WebMListParser parser(kWebMIdSegment);
+  int result = parser.Parse(kBuffer, size, &client_);
+  EXPECT_EQ(-1, result);
+  EXPECT_FALSE(parser.IsParsingComplete());
+}
+
+// Expecting to parse a Cluster, but get a Segment.
+TEST_F(WebMParserTest, ListIdDoesNotMatch) {
+  const uint8 kBuffer[] = {
+    0x18, 0x53, 0x80, 0x67, 0x80,  // SEGMENT (size = 0)
+  };
+  int size = sizeof(kBuffer);
+
+  WebMListParser parser(kWebMIdCluster);
+  int result = parser.Parse(kBuffer, size, &client_);
+  EXPECT_EQ(-1, result);
+  EXPECT_FALSE(parser.IsParsingComplete());
+}
+
+TEST_F(WebMParserTest, InvalidElementInList) {
+  const uint8 kBuffer[] = {
+    0x18, 0x53, 0x80, 0x67, 0x82,  // SEGMENT (size = 2)
+    0xAE, 0x80,  // TrackEntry (size = 0)
+  };
+  int size = sizeof(kBuffer);
+
+  InSequence s;
+  EXPECT_CALL(client_, OnListStart(kWebMIdSegment)).WillOnce(Return(true));
+
+  WebMListParser parser(kWebMIdSegment);
+  int result = parser.Parse(kBuffer, size, &client_);
+  EXPECT_EQ(-1, result);
+  EXPECT_FALSE(parser.IsParsingComplete());
+}
+
+TEST_F(WebMParserTest, VoidAndCRC32InList) {
+  const uint8 kBuffer[] = {
+    0x18, 0x53, 0x80, 0x67, 0x99,  // SEGMENT (size = 25)
+    0xEC, 0x83, 0x00, 0x00, 0x00,  // Void (size = 3)
+    0xBF, 0x83, 0x00, 0x00, 0x00,  // CRC32 (size = 3)
+    0x1F, 0x43, 0xB6, 0x75, 0x8A,  // CLUSTER (size = 10)
+    0xEC, 0x83, 0x00, 0x00, 0x00,  // Void (size = 3)
+    0xBF, 0x83, 0x00, 0x00, 0x00,  // CRC32 (size = 3)
+  };
+  int size = sizeof(kBuffer);
+
+  InSequence s;
+  EXPECT_CALL(client_, OnListStart(kWebMIdSegment)).WillOnce(Return(true));
+  EXPECT_CALL(client_, OnListStart(kWebMIdCluster)).WillOnce(Return(true));
+  EXPECT_CALL(client_, OnListEnd(kWebMIdCluster)).WillOnce(Return(true));
+  EXPECT_CALL(client_, OnListEnd(kWebMIdSegment)).WillOnce(Return(true));
+
+  WebMListParser parser(kWebMIdSegment);
+  int result = parser.Parse(kBuffer, size, &client_);
+  EXPECT_EQ(size, result);
+  EXPECT_TRUE(parser.IsParsingComplete());
+}
+
+
+TEST_F(WebMParserTest, ParseListElementWithSingleCall) {
+  const SimpleBlockInfo kBlockInfo[] = {
+    { 0, 1 },
+    { 1, 2 },
+    { 0, 3 },
+    { 0, 4 },
+    { 1, 4 },
+  };
+  int block_count = arraysize(kBlockInfo);
+
+  scoped_ptr<Cluster> cluster(CreateCluster(0, kBlockInfo, block_count));
+  CreateClusterExpectations(0, kBlockInfo, block_count, &client_);
+
+  WebMListParser parser(kWebMIdCluster);
+  int result = parser.Parse(cluster->data(), cluster->size(), &client_);
+  EXPECT_EQ(cluster->size(), result);
+  EXPECT_TRUE(parser.IsParsingComplete());
+}
+
+TEST_F(WebMParserTest, ParseListElementWithMultipleCalls) {
+  const SimpleBlockInfo kBlockInfo[] = {
+    { 0, 1 },
+    { 1, 2 },
+    { 0, 3 },
+    { 0, 4 },
+    { 1, 4 },
+  };
+  int block_count = arraysize(kBlockInfo);
+
+  scoped_ptr<Cluster> cluster(CreateCluster(0, kBlockInfo, block_count));
+  CreateClusterExpectations(0, kBlockInfo, block_count, &client_);
+
+  const uint8* data = cluster->data();
+  int size = cluster->size();
+  int default_parse_size = 3;
+  WebMListParser parser(kWebMIdCluster);
+  int parse_size = std::min(default_parse_size, size);
+
+  while (size > 0) {
+    int result = parser.Parse(data, parse_size, &client_);
+    EXPECT_GE(result, 0);
+    EXPECT_LE(result, parse_size);
+
+    if (result == 0) {
+      // The parser needs more data so increase the parse_size a little.
+      EXPECT_FALSE(parser.IsParsingComplete());
+      parse_size += default_parse_size;
+      parse_size = std::min(parse_size, size);
+      continue;
+    }
+
+    parse_size = default_parse_size;
+
+    data += result;
+    size -= result;
+
+    EXPECT_EQ((size == 0), parser.IsParsingComplete());
+  }
+  EXPECT_TRUE(parser.IsParsingComplete());
+}
+
+}  // namespace media
diff --git a/media/webm/webm_tracks_parser.cc b/media/webm/webm_tracks_parser.cc
index 29b4f33..7cd9569 100644
--- a/media/webm/webm_tracks_parser.cc
+++ b/media/webm/webm_tracks_parser.cc
@@ -9,21 +9,39 @@
 
 namespace media {
 
+static const base::TimeDelta kNoDuration =
+    base::TimeDelta::FromMicroseconds(-1);
+
 WebMTracksParser::WebMTracksParser(int64 timecode_scale)
     : timecode_scale_(timecode_scale),
       track_type_(-1),
       track_num_(-1),
       track_default_duration_(-1),
       audio_track_num_(-1),
-      audio_default_duration_(base::TimeDelta::FromMicroseconds(-1)),
+      audio_default_duration_(kNoDuration),
       video_track_num_(-1),
-      video_default_duration_(base::TimeDelta::FromMicroseconds(-1)) {
+      video_default_duration_(kNoDuration) {
 }
 
 WebMTracksParser::~WebMTracksParser() {}
 
 int WebMTracksParser::Parse(const uint8* buf, int size) {
-  return WebMParseListElement(buf, size, kWebMIdTracks, 1, this);
+  track_type_ =-1;
+  track_num_ = -1;
+  track_default_duration_ = -1;
+  audio_track_num_ = -1;
+  audio_default_duration_ = kNoDuration;
+  video_track_num_ = -1;
+  video_default_duration_ = kNoDuration;
+
+  WebMListParser parser(kWebMIdTracks);
+  int result = parser.Parse(buf, size, this);
+
+  if (result <= 0)
+    return result;
+
+  // For now we do all or nothing parsing.
+  return parser.IsParsingComplete() ? result : 0;
 }
 
 
@@ -40,9 +58,9 @@ bool WebMTracksParser::OnListStart(int id) {
 bool WebMTracksParser::OnListEnd(int id) {
   if (id == kWebMIdTrackEntry) {
     if (track_type_ == -1 || track_num_ == -1) {
-      VLOG(1) << "Missing TrackEntry data"
-              << " TrackType " << track_type_
-              << " TrackNum " << track_num_;
+      DVLOG(1) << "Missing TrackEntry data"
+               << " TrackType " << track_type_
+               << " TrackNum " << track_num_;
       return false;
     }
 
@@ -57,7 +75,7 @@ bool WebMTracksParser::OnListEnd(int id) {
       audio_track_num_ = track_num_;
       audio_default_duration_ = default_duration;
     } else {
-      VLOG(1) << "Unexpected TrackType " << track_type_;
+      DVLOG(1) << "Unexpected TrackType " << track_type_;
       return false;
     }
 
@@ -86,7 +104,7 @@ bool WebMTracksParser::OnUInt(int id, int64 val) {
   }
 
   if (*dst != -1) {
-    VLOG(1) << "Multiple values for id " << std::hex << id << " specified";
+    DVLOG(1) << "Multiple values for id " << std::hex << id << " specified";
     return false;
   }
 
@@ -95,7 +113,7 @@ bool WebMTracksParser::OnUInt(int id, int64 val) {
 }
 
 bool WebMTracksParser::OnFloat(int id, double val) {
-  VLOG(1) << "Unexpected float for id" << std::hex << id;
+  DVLOG(1) << "Unexpected float for id" << std::hex << id;
   return false;
 }
 
@@ -108,7 +126,7 @@ bool WebMTracksParser::OnString(int id, const std::string& str) {
     return false;
 
   if (str != "A_VORBIS" && str != "V_VP8") {
-    VLOG(1) << "Unexpected CodecID " << str;
+    DVLOG(1) << "Unexpected CodecID " << str;
     return false;
   }