Fix incorrect opus seek preroll and flaky pre-skip removal.

media/filters/opus_audio_decoder.cc

Index: media/filters/opus_audio_decoder.cc
diff --git a/media/filters/opus_audio_decoder.cc b/media/filters/opus_audio_decoder.cc
index 181f34014da4f0b9b011c1381b94a886440154e8..abfa13b27f74eae51461ce6eb63ec13b6c61a866 100644
--- a/media/filters/opus_audio_decoder.cc
+++ b/media/filters/opus_audio_decoder.cc
@@ -245,9 +245,7 @@ static bool ParseOpusExtraData(const uint8* data, int data_size,
 
 OpusAudioDecoder::OpusAudioDecoder(
     const scoped_refptr<base::SingleThreadTaskRunner>& task_runner)
-    : task_runner_(task_runner),
-      opus_decoder_(NULL),
-      start_input_timestamp_(kNoTimestamp()) {}
+    : task_runner_(task_runner), opus_decoder_(nullptr) {}
 
 std::string OpusAudioDecoder::GetDisplayName() const {
   return "OpusAudioDecoder";
@@ -293,7 +291,6 @@ OpusAudioDecoder::~OpusAudioDecoder() {
     return;
 
   opus_multistream_decoder_ctl(opus_decoder_, OPUS_RESET_STATE);
-  ResetTimestampState();
   CloseDecoder();
 }
 
@@ -319,14 +316,6 @@ void OpusAudioDecoder::DecodeBuffer(
     return;
   }
 
-  // Apply the necessary codec delay.
-  if (start_input_timestamp_ == kNoTimestamp())

[chcunningham, 2015/07/31 19:48:44]

Am I right that what you removed here is equivalent behavior to what we have
now? That is, we used to set start_timestamp with the TS from the first buffer
and configure the discard_helper with preskip. Now we just we configure the
discard helper as soon as the configuration arrives. The effect in both cases is
that we discard the first so many buffers we see (and adjust timestamps) until
preskip is satisfied. If I'm right, the new way is definitely cleaner, but it
makes me wonder if I've missed something. The change description suggests to me
that the original behavior was different/wrong.

[DaleCurtis, 2015/08/03 22:49:53]

Kind of, in the first playback case the behavior is similar. As noted in the
description, however subsequent playbacks or seeks would do the wrong thing and
be initialized with the seek preroll instead of the codec delay though.

-    start_input_timestamp_ = input->timestamp();
-  if (!discard_helper_->initialized() &&
-      input->timestamp() == start_input_timestamp_) {
-    discard_helper_->Reset(config_.codec_delay());
-  }
-
   scoped_refptr<AudioBuffer> output_buffer;
 
   if (!Decode(input, &output_buffer)) {
@@ -420,22 +409,21 @@ bool OpusAudioDecoder::ConfigureDecoder() {
     return false;
   }
 
-  discard_helper_.reset(
-      new AudioDiscardHelper(config_.samples_per_second(), 0));
-  start_input_timestamp_ = kNoTimestamp();
+  ResetTimestampState();
   return true;
 }
 
 void OpusAudioDecoder::CloseDecoder() {
   if (opus_decoder_) {
     opus_multistream_decoder_destroy(opus_decoder_);
-    opus_decoder_ = NULL;
+    opus_decoder_ = nullptr;
   }
 }
 
 void OpusAudioDecoder::ResetTimestampState() {
-  discard_helper_->Reset(
-      discard_helper_->TimeDeltaToFrames(config_.seek_preroll()));
+  discard_helper_.reset(
+      new AudioDiscardHelper(config_.samples_per_second(), 0));
+  discard_helper_->Reset(config_.codec_delay());
 }
 
 bool OpusAudioDecoder::Decode(const scoped_refptr<DecoderBuffer>& input,
@@ -479,7 +467,7 @@ bool OpusAudioDecoder::Decode(const scoped_refptr<DecoderBuffer>& input,
 
   // Handles discards and timestamping.  Discard the buffer if more data needed.
   if (!discard_helper_->ProcessBuffers(input, *output_buffer))
-    *output_buffer = NULL;
+    *output_buffer = nullptr;
 
   return true;
 }