Use av_rescale_q() for converting FFmpeg timestamps to base::TimeDelta.

Previously we were using integer math to convert to microseconds, but depending on the frame rate and packet size we could introduce enough error that could accumulate and introduce audio/video synchronization drift.  av_rescale_q() is a simple function but is designed to minimize error as much as possible.

Review URL: http://codereview.chromium.org/113598

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@16453 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 10 insertions, 1 deletions

diff --git a/media/base/media_posix.cc b/media/base/media_posix.cc
index 4bddf6d..94c1a89 100644
--- a/media/base/media_posix.cc
+++ b/media/base/media_posix.cc
@@ -122,6 +122,11 @@ void av_free(void* ptr) {
   return av_free_ptr(ptr);
 }
 
+int64_t (*av_rescale_q_ptr)(int64_t a, AVRational bq, AVRational cq) = NULL;
+int64_t av_rescale_q(int64_t a, AVRational bq, AVRational cq) {
+  return av_rescale_q_ptr(a, bq, cq);
+}
+
 }  // extern "C"
 
 
@@ -240,6 +245,9 @@ bool InitializeMediaLibrary(const FilePath& module_dir) {
   av_free_ptr =
       reinterpret_cast<void (*)(void*)>(
           dlsym(libs[FILE_LIBAVUTIL], "av_free"));
+  av_rescale_q_ptr =
+      reinterpret_cast<int64_t (*)(int64_t, AVRational, AVRational)>(
+          dlsym(libs[FILE_LIBAVUTIL], "av_rescale_q"));
 
   // Check that all the symbols were loaded correctly before returning true.
   if (av_get_bits_per_sample_format_ptr &&
@@ -259,7 +267,8 @@ bool InitializeMediaLibrary(const FilePath& module_dir) {
       av_register_protocol_ptr &&
 
       av_malloc_ptr &&
-      av_free_ptr) {
+      av_free_ptr &&
+      av_rescale_q_ptr) {
     return true;
   }