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, we just drop any discard padding if |discard_frames_|
 108       // consumes the entire buffer.
 109       return false;
 110     }
 111
 112     decoded_buffer->TrimStart(frames_to_discard);
 113   }
 114
 115   // Process any delayed end discard from the previous buffer.
 116   if (delayed_end_discard_ > 0) {
 117     DCHECK_GT(decoder_delay_, 0u);
 118
 119     const size_t discard_index = decoder_delay_ - delayed_end_discard_;
 120     DCHECK_LT(discard_index, decoder_delay_);
 121
 122     const size_t decoded_frames = decoded_buffer->frame_count();
 123     DCHECK_LT(delayed_end_discard_, decoded_frames);
 124
 125     DVLOG(1) << "Delayed end discard of " << delayed_end_discard_ << " out of "
 126              << decoded_frames << " frames starting at " << discard_index;
 127
 128     decoded_buffer->TrimRange(discard_index,
 129                               discard_index + delayed_end_discard_);
 130     delayed_end_discard_ = 0;
 131   }
 132
 133   // Handle front discard padding.
 134   if (current_discard_padding.first > base::TimeDelta()) {
 135     const size_t decoded_frames = decoded_buffer->frame_count();
 136
 137     // If a complete buffer discard is requested and there's no decoder delay,
 138     // just discard all remaining frames from this buffer.  With decoder delay
 139     // we have to estimate the correct number of frames to discard based on the
 140     // duration of the encoded buffer.
 141     const size_t start_frames_to_discard =
 142         current_discard_padding.first == kInfiniteDuration()
 143             ? (decoder_delay_ > 0
 144                    ? TimeDeltaToFrames(encoded_buffer->duration())
 145                    : decoded_frames)
 146             : TimeDeltaToFrames(current_discard_padding.first);
 147
 148     // Regardless of the timestamp on the encoded buffer, the corresponding
 149     // decoded output will appear |decoder_delay_| frames later.
 150     size_t discard_start = decoder_delay_;
 151     if (decoder_delay_ > 0) {
 152       // If we have a |decoder_delay_| and have already discarded frames from
 153       // this buffer, the |discard_start| must be adjusted by the number of
 154       // frames already discarded.
 155       const size_t frames_discarded_so_far =
 156           original_frame_count - decoded_buffer->frame_count();
 157       CHECK_LE(frames_discarded_so_far, decoder_delay_);
 158       discard_start -= frames_discarded_so_far;
 159     }
 160
 161     // For simplicity require the start of the discard to be within the current
 162     // buffer.  Doing so allows us avoid complexity around tracking discards
 163     // across buffers.
 164     CHECK_LT(discard_start, decoded_frames);
 165
 166     const size_t frames_to_discard =
 167         std::min(start_frames_to_discard, decoded_frames - discard_start);
 168
 169     // Carry over any frames which need to be discarded from the front of the
 170     // next buffer.
 171     DCHECK(!discard_frames_);
 172     discard_frames_ = start_frames_to_discard - frames_to_discard;
 173
 174     DVLOG(1) << "Front discard of " << frames_to_discard << " out of "
 175              << decoded_frames << " frames starting at " << discard_start;
 176
 177     // If everything would be discarded, indicate a new buffer is required.
 178     if (frames_to_discard == decoded_frames) {
 179       // The buffer should not have been marked with end discard if the front
 180       // discard removes everything.
 181       DCHECK(current_discard_padding.second == base::TimeDelta());
 182       return false;
 183     }
 184
 185     decoded_buffer->TrimRange(discard_start, discard_start + frames_to_discard);
 186   } else {
 187     DCHECK(current_discard_padding.first == base::TimeDelta());
 188   }
 189
 190   // Handle end discard padding.
 191   if (current_discard_padding.second > base::TimeDelta()) {
 192     const size_t decoded_frames = decoded_buffer->frame_count();
 193     size_t end_frames_to_discard =
 194         TimeDeltaToFrames(current_discard_padding.second);
 195
 196     if (decoder_delay_) {
 197       // Delayed end discard only works if the decoder delay is less than a
 198       // single buffer.
 199       DCHECK_LT(decoder_delay_, original_frame_count);
 200
 201       // If the discard is >= the decoder delay, trim everything we can off the
 202       // end of this buffer and the rest from the start of the next.
 203       if (end_frames_to_discard >= decoder_delay_) {
 204         DCHECK(!discard_frames_);
 205         discard_frames_ = decoder_delay_;
 206         end_frames_to_discard -= decoder_delay_;
 207       } else {
 208         DCHECK(!delayed_end_discard_);
 209         std::swap(delayed_end_discard_, end_frames_to_discard);
 210       }
 211     }
 212
 213     if (end_frames_to_discard > decoded_frames) {
 214       DLOG(ERROR) << "Encountered invalid discard padding value.";
 215       return false;
 216     }
 217
 218     if (end_frames_to_discard > 0) {
 219       DVLOG(1) << "End discard of " << end_frames_to_discard << " out of "
 220                << decoded_frames;
 221
 222       // If everything would be discarded, indicate a new buffer is required.
 223       if (end_frames_to_discard == decoded_frames)
 224         return false;
 225
 226       decoded_buffer->TrimEnd(end_frames_to_discard);
 227     }
 228   } else {
 229     DCHECK(current_discard_padding.second == base::TimeDelta());
 230   }
 231
 232   // Assign timestamp to the buffer.
 233   decoded_buffer->set_timestamp(timestamp_helper_.GetTimestamp());
 234   timestamp_helper_.AddFrames(decoded_buffer->frame_count());
 235   return true;
 236 }
 237
 238 }  // namespace media