media/base/audio_discard_helper.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "media/base/audio_discard_helper.h"
   6
   7 #include <algorithm>
   8
   9 #include "base/logging.h"
  10 #include "media/base/audio_buffer.h"
  11
  12 namespace media {
  13
  14 static void WarnOnNonMonotonicTimestamps(base::TimeDelta last_timestamp,
  15                                          base::TimeDelta current_timestamp) {
  16   if (last_timestamp == kNoTimestamp() || last_timestamp < current_timestamp)
  17     return;
  18
  19   const base::TimeDelta diff = current_timestamp - last_timestamp;
  20   DLOG(WARNING) << "Input timestamps are not monotonically increasing! "
  21                 << " ts " << current_timestamp.InMicroseconds() << " us"
  22                 << " diff " << diff.InMicroseconds() << " us";
  23 }
  24
  25 AudioDiscardHelper::AudioDiscardHelper(int sample_rate, size_t decoder_delay)
  26     : sample_rate_(sample_rate),
  27       decoder_delay_(decoder_delay),
  28       timestamp_helper_(sample_rate_),
  29       discard_frames_(0),
  30       last_input_timestamp_(kNoTimestamp()),
  31       delayed_discard_(false),
  32       delayed_end_discard_(0) {
  33   DCHECK_GT(sample_rate_, 0);
  34 }
  35
  36 AudioDiscardHelper::~AudioDiscardHelper() {
  37 }
  38
  39 size_t AudioDiscardHelper::TimeDeltaToFrames(base::TimeDelta duration) const {
  40   DCHECK(duration >= base::TimeDelta());
  41   return duration.InSecondsF() * sample_rate_ + 0.5;
  42 }
  43
  44 void AudioDiscardHelper::Reset(size_t initial_discard) {
  45   discard_frames_ = initial_discard;
  46   last_input_timestamp_ = kNoTimestamp();
  47   timestamp_helper_.SetBaseTimestamp(kNoTimestamp());
  48   delayed_discard_ = false;
  49   delayed_discard_padding_ = DecoderBuffer::DiscardPadding();
  50 }
  51
  52 bool AudioDiscardHelper::ProcessBuffers(
  53     const scoped_refptr<DecoderBuffer>& encoded_buffer,
  54     const scoped_refptr<AudioBuffer>& decoded_buffer) {
  55   DCHECK(!encoded_buffer->end_of_stream());
  56   DCHECK(encoded_buffer->timestamp() != kNoTimestamp());
  57
  58   // Issue a debug warning when we see non-monotonic timestamps.  Only a warning
  59   // to allow chained OGG playback.
  60   WarnOnNonMonotonicTimestamps(last_input_timestamp_,
  61                                encoded_buffer->timestamp());
  62   last_input_timestamp_ = encoded_buffer->timestamp();
  63
  64   // If this is the first buffer seen, setup the timestamp helper.
  65   const bool first_buffer = !initialized();
  66   if (first_buffer) {
  67     // Clamp the base timestamp to zero.
  68     timestamp_helper_.SetBaseTimestamp(
  69         std::max(base::TimeDelta(), encoded_buffer->timestamp()));
  70   }
  71   DCHECK(initialized());
  72
  73   if (!decoded_buffer.get()) {
  74     // If there's a one buffer delay for decoding, we need to save it so it can
  75     // be processed with the next decoder buffer.
  76     if (first_buffer) {
  77       delayed_discard_ = true;
  78       delayed_discard_padding_ = encoded_buffer->discard_padding();
  79     }
  80     return false;
  81   }
  82
  83   const size_t original_frame_count = decoded_buffer->frame_count();
  84
  85   // If there's a one buffer delay for decoding, pick up the last encoded
  86   // buffer's discard padding for processing with the current decoded buffer.
  87   DecoderBuffer::DiscardPadding current_discard_padding =
  88       encoded_buffer->discard_padding();
  89   if (delayed_discard_) {
  90     // For simplicity disallow cases where decoder delay is present with delayed
  91     // discard (no codecs at present).  Doing so allows us to avoid complexity
  92     // around endpoint tracking when handling complete buffer discards.
  93     DCHECK_EQ(decoder_delay_, 0u);
  94     std::swap(current_discard_padding, delayed_discard_padding_);
  95   }
  96
  97   if (discard_frames_ > 0) {
  98     const size_t decoded_frames = decoded_buffer->frame_count();
  99     const size_t frames_to_discard = std::min(discard_frames_, decoded_frames);
 100     discard_frames_ -= frames_to_discard;
 101
 102     DVLOG(1) << "Initial discard of " << frames_to_discard << " out of "
 103              << decoded_frames << " frames.";
 104
 105     // If everything would be discarded, indicate a new buffer is required.
 106     if (frames_to_discard == decoded_frames) {
 107       // For simplicity disallow cases where a buffer with discard padding is
 108       // present.  Doing so allows us to avoid complexity around tracking
 109       // discards across buffers.
 110       DCHECK(current_discard_padding.first == base::TimeDelta());
 111       DCHECK(current_discard_padding.second == base::TimeDelta());
 112       return false;
 113     }
 114
 115     decoded_buffer->TrimStart(frames_to_discard);
 116   }
 117
 118   // Process any delayed end discard from the previous buffer.
 119   if (delayed_end_discard_ > 0) {
 120     DCHECK_GT(decoder_delay_, 0u);
 121
 122     const size_t discard_index = decoder_delay_ - delayed_end_discard_;
 123     DCHECK_LT(discard_index, decoder_delay_);
 124
 125     const size_t decoded_frames = decoded_buffer->frame_count();
 126     DCHECK_LT(delayed_end_discard_, decoded_frames);
 127
 128     DVLOG(1) << "Delayed end discard of " << delayed_end_discard_ << " out of "
 129              << decoded_frames << " frames starting at " << discard_index;
 130
 131     decoded_buffer->TrimRange(discard_index,
 132                               discard_index + delayed_end_discard_);
 133     delayed_end_discard_ = 0;
 134   }
 135
 136   // Handle front discard padding.
 137   if (current_discard_padding.first > base::TimeDelta()) {
 138     const size_t decoded_frames = decoded_buffer->frame_count();
 139
 140     // If a complete buffer discard is requested and there's no decoder delay,
 141     // just discard all remaining frames from this buffer.  With decoder delay
 142     // we have to estimate the correct number of frames to discard based on the
 143     // duration of the encoded buffer.
 144     const size_t start_frames_to_discard =
 145         current_discard_padding.first == kInfiniteDuration()
 146             ? (decoder_delay_ > 0
 147                    ? TimeDeltaToFrames(encoded_buffer->duration())
 148                    : decoded_frames)
 149             : TimeDeltaToFrames(current_discard_padding.first);
 150
 151     // Regardless of the timestamp on the encoded buffer, the corresponding
 152     // decoded output will appear |decoder_delay_| frames later.
 153     size_t discard_start = decoder_delay_;
 154     if (decoder_delay_ > 0) {
 155       // If we have a |decoder_delay_| and have already discarded frames from
 156       // this buffer, the |discard_start| must be adjusted by the number of
 157       // frames already discarded.
 158       const size_t frames_discarded_so_far =
 159           original_frame_count - decoded_buffer->frame_count();
 160       CHECK_LE(frames_discarded_so_far, decoder_delay_);
 161       discard_start -= frames_discarded_so_far;
 162     }
 163
 164     // For simplicity require the start of the discard to be within the current
 165     // buffer.  Doing so allows us avoid complexity around tracking discards
 166     // across buffers.
 167     CHECK_LT(discard_start, decoded_frames);
 168
 169     const size_t frames_to_discard =
 170         std::min(start_frames_to_discard, decoded_frames - discard_start);
 171
 172     // Carry over any frames which need to be discarded from the front of the
 173     // next buffer.
 174     DCHECK(!discard_frames_);
 175     discard_frames_ = start_frames_to_discard - frames_to_discard;
 176
 177     DVLOG(1) << "Front discard of " << frames_to_discard << " out of "
 178              << decoded_frames << " frames starting at " << discard_start;
 179
 180     // If everything would be discarded, indicate a new buffer is required.
 181     if (frames_to_discard == decoded_frames) {
 182       // The buffer should not have been marked with end discard if the front
 183       // discard removes everything.
 184       DCHECK(current_discard_padding.second == base::TimeDelta());
 185       return false;
 186     }
 187
 188     decoded_buffer->TrimRange(discard_start, discard_start + frames_to_discard);
 189   } else {
 190     DCHECK(current_discard_padding.first == base::TimeDelta());
 191   }
 192
 193   // Handle end discard padding.
 194   if (current_discard_padding.second > base::TimeDelta()) {
 195     const size_t decoded_frames = decoded_buffer->frame_count();
 196     size_t end_frames_to_discard =
 197         TimeDeltaToFrames(current_discard_padding.second);
 198
 199     if (decoder_delay_) {
 200       // Delayed end discard only works if the decoder delay is less than a
 201       // single buffer.
 202       DCHECK_LT(decoder_delay_, original_frame_count);
 203
 204       // If the discard is >= the decoder delay, trim everything we can off the
 205       // end of this buffer and the rest from the start of the next.
 206       if (end_frames_to_discard >= decoder_delay_) {
 207         DCHECK(!discard_frames_);
 208         discard_frames_ = decoder_delay_;
 209         end_frames_to_discard -= decoder_delay_;
 210       } else {
 211         DCHECK(!delayed_end_discard_);
 212         std::swap(delayed_end_discard_, end_frames_to_discard);
 213       }
 214     }
 215
 216     if (end_frames_to_discard > decoded_frames) {
 217       DLOG(ERROR) << "Encountered invalid discard padding value.";
 218       return false;
 219     }
 220
 221     if (end_frames_to_discard > 0) {
 222       DVLOG(1) << "End discard of " << end_frames_to_discard << " out of "
 223                << decoded_frames;
 224
 225       // If everything would be discarded, indicate a new buffer is required.
 226       if (end_frames_to_discard == decoded_frames)
 227         return false;
 228
 229       decoded_buffer->TrimEnd(end_frames_to_discard);
 230     }
 231   } else {
 232     DCHECK(current_discard_padding.second == base::TimeDelta());
 233   }
 234
 235   // Assign timestamp to the buffer.
 236   decoded_buffer->set_timestamp(timestamp_helper_.GetTimestamp());
 237   timestamp_helper_.AddFrames(decoded_buffer->frame_count());
 238   return true;
 239 }
 240
 241 }  // namespace media