// Copyright 2014 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. #ifndef MEDIA_BASE_AUDIO_DISCARD_HELPER_H_ #define MEDIA_BASE_AUDIO_DISCARD_HELPER_H_ #include "base/memory/ref_counted.h" #include "base/time/time.h" #include "media/base/audio_timestamp_helper.h" #include "media/base/decoder_buffer.h" #include "media/base/media_export.h" #include "media/base/timestamp_constants.h" namespace media { class AudioBuffer; // Helper class for managing timestamps and discard events around decoding. class MEDIA_EXPORT AudioDiscardHelper { public: // |sample_rate| is the sample rate of decoded data which will be handed into // the ProcessBuffers() call. // // |decoder_delay| is the number of frames a decoder will output before data // corresponding to the first encoded buffer is output. Callers only need to // specify this if the decoder inserts frames which have no corresponding // encoded buffer. // // For example, most MP3 decoders will output 529 junk frames before the data // corresponding to the first encoded buffer is output. These frames are not // represented in the encoded data stream and instead are an artifact of how // most MP3 decoders work. See http://lame.sourceforge.net/tech-FAQ.txt AudioDiscardHelper(int sample_rate, size_t decoder_delay); ~AudioDiscardHelper(); // Converts a TimeDelta to a frame count based on the constructed sample rate. // |duration| must be positive. size_t TimeDeltaToFrames(base::TimeDelta duration) const; // Resets internal state and indicates that |initial_discard| of upcoming // frames should be discarded. void Reset(size_t initial_discard); // Applies discard padding from the encoded buffer along with any initial // discards. |decoded_buffer| may be NULL, if not the timestamp and duration // will be set after discards are applied. Returns true if |decoded_buffer| // exists after processing discard events. Returns false if |decoded_buffer| // was NULL, is completely discarded, or a processing error occurs. // // If AudioDiscardHelper is not initialized() the timestamp of the first // |encoded_buffer| will be used as the basis for all future timestamps set on // |decoded_buffer|s. If the first buffer has a negative timestamp it will be // clamped to zero. bool ProcessBuffers(const scoped_refptr& encoded_buffer, const scoped_refptr& decoded_buffer); // Whether any buffers have been processed. bool initialized() const { return timestamp_helper_.base_timestamp() != kNoTimestamp(); } private: // The sample rate of the decoded audio samples. Used by TimeDeltaToFrames() // and the timestamp helper. const int sample_rate_; // Some codecs output extra samples during the first decode. In order to trim // DiscardPadding correctly the helper must know the offset into the decoded // buffers at which real samples start. const size_t decoder_delay_; // Used to regenerate sample accurate timestamps for decoded buffers. The // timestamp of the first encoded buffer seen by ProcessBuffers() is used as // the base timestamp. AudioTimestampHelper timestamp_helper_; // The number of frames to discard from the front of the next buffer. Can be // set by Reset() and added to by a front DiscardPadding larger than its // associated buffer. size_t discard_frames_; // The last encoded buffer timestamp seen by ProcessBuffers() or kNoTimestamp // if no buffers have been seen thus far. Used to issue warnings for buffer // sequences with non-monotonic timestamps. base::TimeDelta last_input_timestamp_; // Certain codecs require two encoded buffers before they'll output the first // decoded buffer. In this case DiscardPadding must be carried over from the // previous encoded buffer. Enabled automatically if an encoded buffer is // given to ProcessBuffers() with a NULL decoded buffer. bool delayed_discard_; DecoderBuffer::DiscardPadding delayed_discard_padding_; // When |decoder_delay_| > 0, the number of frames which should be discarded // from the next buffer. The index at which to start discarding is calculated // by subtracting |delayed_end_discard_| from |decoder_delay_|. size_t delayed_end_discard_; DISALLOW_IMPLICIT_CONSTRUCTORS(AudioDiscardHelper); }; } // namespace media #endif // MEDIA_BASE_AUDIO_DISCARD_HELPER_H_