1 // Copyright 2014 The Chromium Authors
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef MEDIA_FILTERS_AUDIO_CLOCK_H_
6 #define MEDIA_FILTERS_AUDIO_CLOCK_H_
12 #include "base/containers/circular_deque.h"
13 #include "base/time/time.h"
14 #include "media/base/media_export.h"
18 // Models a queue of buffered audio in a playback pipeline for use with
19 // estimating the amount of delay in wall clock time. Takes changes in playback
20 // rate into account to handle scenarios where multiple rates may be present in
21 // a playback pipeline with large delay.
26 // Prior to starting audio playback, construct an AudioClock with an initial
27 // media timestamp and a sample rate matching the sample rate the audio device
30 // Each time the audio rendering callback is executed, call WroteAudio() once
31 // (and only once!) containing information on what was written:
32 // 1) How many frames of audio data requested
33 // 2) How many frames of audio data provided
34 // 3) The playback rate of the audio data provided
35 // 4) The current amount of delay
37 // After a call to WroteAudio(), clients can inspect the resulting media
38 // timestamp. This can be used for UI purposes, synchronizing video, etc...
43 // Silence (whether caused by the initial audio delay or failing to write the
44 // amount of requested frames due to underflow) is also modeled and will cause
45 // the media timestamp to stop increasing until all known silence has been
46 // played. AudioClock's model is initialized with silence during the first call
47 // to WroteAudio() using the delay value.
49 // Playback rates are tracked for translating frame durations into media
50 // durations. Since silence doesn't affect media timestamps, it also isn't
51 // affected by playback rates.
52 class MEDIA_EXPORT AudioClock {
54 AudioClock(base::TimeDelta start_timestamp, int sample_rate);
56 AudioClock(const AudioClock&) = delete;
57 AudioClock& operator=(const AudioClock&) = delete;
61 // |frames_written| amount of audio data scaled to |playback_rate| written.
62 // |frames_requested| amount of audio data requested by hardware.
63 // |delay_frames| is the current amount of hardware delay.
64 void WroteAudio(int frames_written,
67 double playback_rate);
69 // If WroteAudio() calls are suspended (i.e. due to playback being paused) the
70 // AudioClock will not properly advance time (even though all data up until
71 // back_timestamp() will playout on the physical device).
73 // To compensate for this, when calls resume, before the next WroteAudio(),
74 // callers should call CompensateForSuspendedWrites() to advance the clock for
75 // audio which continued playing out while WroteAudio() calls were suspended.
77 // |delay_frames| must be provided to properly prime the clock to compensate
78 // for a new initial delay.
79 void CompensateForSuspendedWrites(base::TimeDelta elapsed, int delay_frames);
81 // Returns the bounds of media data currently buffered by the audio hardware,
82 // taking silence and changes in playback rate into account. Buffered audio
83 // structure and timestamps are updated with every call to WroteAudio().
85 // start_timestamp = 1000 ms sample_rate = 40 Hz
86 // +-----------------------+-----------------------+-----------------------+
87 // | 10 frames silence | 20 frames @ 1.0x | 20 frames @ 0.5x |
88 // | = 250 ms (wall) | = 500 ms (wall) | = 500 ms (wall) |
89 // | = 0 ms (media) | = 500 ms (media) | = 250 ms (media) |
90 // +-----------------------+-----------------------+-----------------------+
92 // front_timestamp() is equal to back_timestamp() is equal to
93 // |start_timestamp| since no amount of media frames tracked
94 // media data has been played yet. by AudioClock, which would be
95 // 1000 + 500 + 250 = 1750 ms.
96 base::TimeDelta front_timestamp() const {
97 return base::Microseconds(std::round(front_timestamp_micros_));
99 base::TimeDelta back_timestamp() const {
100 return base::Microseconds(std::round(back_timestamp_micros_));
103 // Returns the amount of wall time until |timestamp| will be played by the
106 // |timestamp| must be within front_timestamp() and back_timestamp().
107 base::TimeDelta TimeUntilPlayback(base::TimeDelta timestamp) const;
109 void ContiguousAudioDataBufferedForTesting(
110 base::TimeDelta* total,
111 base::TimeDelta* same_rate_total) const;
114 // Even with a ridiculously high sample rate of 256kHz, using 64 bits will
115 // permit tracking up to 416999965 days worth of time (that's 1141 millenia).
117 // 32 bits on the other hand would top out at measly 2 hours and 20 minutes.
119 AudioData(int64_t frames, double playback_rate);
122 double playback_rate;
125 // Helpers for operating on |buffered_|.
126 void PushBufferedAudioData(int64_t frames, double playback_rate);
127 void PopBufferedAudioData(int64_t frames);
128 double ComputeBufferedMediaDurationMicros() const;
130 const base::TimeDelta start_timestamp_;
131 const double microseconds_per_frame_;
133 base::circular_deque<AudioData> buffered_;
134 int64_t total_buffered_frames_;
136 // Use double rather than TimeDelta to avoid loss of partial microseconds when
137 // converting between frames-written/delayed and time-passed (see conversion
138 // in WroteAudio()). Particularly for |back_timestamp|, which accumulates more
139 // time with each call to WroteAudio(), the loss of precision can accumulate
140 // to create noticeable audio/video sync drift for longer (2-3 hr) videos.
141 // See http://crbug.com/564604.
142 double front_timestamp_micros_;
143 double back_timestamp_micros_;
148 #endif // MEDIA_FILTERS_AUDIO_CLOCK_H_