Add plumbing and support for crossfading StreamParserBuffers.

media/filters/source_buffer_stream.cc

Index: media/filters/source_buffer_stream.cc
diff --git a/media/filters/source_buffer_stream.cc b/media/filters/source_buffer_stream.cc
index 20e9156ad02e207ed8b676deac038553d6cafdeb..3d8a6c21586574c7faa7ee7f2f99c3992a69b968 100644
--- a/media/filters/source_buffer_stream.cc
+++ b/media/filters/source_buffer_stream.cc
@@ -341,7 +341,8 @@ SourceBufferStream::SourceBufferStream(const AudioDecoderConfig& audio_config,
       last_output_buffer_timestamp_(kNoTimestamp()),
       max_interbuffer_distance_(kNoTimestamp()),
       memory_limit_(kDefaultAudioMemoryLimit),
-      config_change_pending_(false) {
+      config_change_pending_(false),
+      fade_out_preroll_index_(0) {
   DCHECK(audio_config.IsValidConfig());
   audio_configs_.push_back(audio_config);
 }
@@ -363,7 +364,8 @@ SourceBufferStream::SourceBufferStream(const VideoDecoderConfig& video_config,
       last_output_buffer_timestamp_(kNoTimestamp()),
       max_interbuffer_distance_(kNoTimestamp()),
       memory_limit_(kDefaultVideoMemoryLimit),
-      config_change_pending_(false) {
+      config_change_pending_(false),
+      fade_out_preroll_index_(0) {
   DCHECK(video_config.IsValidConfig());
   video_configs_.push_back(video_config);
 }
@@ -386,7 +388,8 @@ SourceBufferStream::SourceBufferStream(const TextTrackConfig& text_config,
       last_output_buffer_timestamp_(kNoTimestamp()),
       max_interbuffer_distance_(kNoTimestamp()),
       memory_limit_(kDefaultAudioMemoryLimit),
-      config_change_pending_(false) {
+      config_change_pending_(false),
+      fade_out_preroll_index_(0) {
 }
 
 SourceBufferStream::~SourceBufferStream() {
@@ -670,6 +673,8 @@ void SourceBufferStream::ResetSeekState() {
   track_buffer_.clear();
   config_change_pending_ = false;
   last_output_buffer_timestamp_ = kNoTimestamp();
+  fade_out_preroll_index_ = 0;
+  fade_in_buffer_ = NULL;
 }
 
 bool SourceBufferStream::ShouldSeekToStartOfBuffered(
@@ -1092,17 +1097,78 @@ void SourceBufferStream::OnSetDuration(base::TimeDelta duration) {
 
 SourceBufferStream::Status SourceBufferStream::GetNextBuffer(
     scoped_refptr<StreamParserBuffer>* out_buffer) {
+  if (!fade_in_buffer_) {
+    const SourceBufferStream::Status status = GetNextBufferInternal(out_buffer);
+
+    // Just return if GetNextBufferInternal() failed or there's no fade out
+    // preroll, there's nothing else to do.
+    if (status != SourceBufferStream::kSuccess ||
+        (*out_buffer)->GetFadeOutPreroll().empty()) {
+      return status;
+    }
+
+    // Setup fade in buffer and fall through into splice frame buffer handling.
+    fade_out_preroll_index_ = 0;
+    fade_in_buffer_ = *out_buffer;
+  }
+
+  DCHECK(fade_in_buffer_);
+  const std::vector<scoped_refptr<StreamParserBuffer> >& fade_out_preroll =
+      fade_in_buffer_->GetFadeOutPreroll();
+
+  // Are there any fade out buffers left to hand out?
+  if (fade_out_preroll_index_ < fade_out_preroll.size()) {
+    // Account for config changes which occur between fade out buffers.
+    if (current_config_index_ !=
+        fade_out_preroll.at(fade_out_preroll_index_)->GetConfigId()) {
+      config_change_pending_ = true;
+      DVLOG(1) << "Config change (fade out preroll config ID does not match).";
+      return SourceBufferStream::kConfigChange;
+    }
+
+    *out_buffer = fade_out_preroll.at(fade_out_preroll_index_++);
+    return SourceBufferStream::kSuccess;
+  }
+
+  // Did we hand out the last fade out buffer on the last call?
+  if (fade_out_preroll_index_ == fade_out_preroll.size()) {
+    fade_out_preroll_index_++;
+    config_change_pending_ = true;
+    DVLOG(1) << "Config change (forced for fade in of splice frame).";
+    return SourceBufferStream::kConfigChange;
+  }
+
+  // All fade out buffers have been handed out and a config change completed, so
+  // hand out the final buffer for fade in.  Because a config change has already
+  // been issued, we don't need to account for

[acolwell GONE FROM CHROMIUM, 2014/01/10 22:53:31]

nit: Finish the sentence. :)

[DaleCurtis, 2014/01/10 23:03:49]

Haha, awesome, I accidentally a sentence.

+  DCHECK_GT(fade_out_preroll_index_, fade_out_preroll.size());
+  *out_buffer = fade_in_buffer_;
+  fade_in_buffer_ = NULL;
+  fade_out_preroll_index_ = 0;
+  return SourceBufferStream::kSuccess;
+}
+
+SourceBufferStream::Status SourceBufferStream::GetNextBufferInternal(
+    scoped_refptr<StreamParserBuffer>* out_buffer) {
   CHECK(!config_change_pending_);
 
   if (!track_buffer_.empty()) {
     DCHECK(!selected_range_);
-    if (track_buffer_.front()->GetConfigId() != current_config_index_) {
+    scoped_refptr<StreamParserBuffer>& next_buffer = track_buffer_.front();
+
+    // If the next buffer is an audio splice frame, the next effective config id
+    // comes from the first fade out preroll buffer.
+    const int next_config_id = next_buffer->GetFadeOutPreroll().empty() ?
+        next_buffer->GetConfigId() :
+        next_buffer->GetFadeOutPreroll().at(0)->GetConfigId();

[acolwell GONE FROM CHROMIUM, 2014/01/10 22:53:31]

nit: Any reason you can't use the [0] instead of .at(0)? Similar comment in
other at() instances.

[DaleCurtis, 2014/01/10 23:03:49]

I switched to .at() since that seemed to be the style in SourceBufferRange.  I
see now that both styles are used.  Which would you prefer?

+
+    if (next_config_id != current_config_index_) {
       config_change_pending_ = true;
       DVLOG(1) << "Config change (track buffer config ID does not match).";
       return kConfigChange;
     }
 
-    *out_buffer = track_buffer_.front();
+    *out_buffer = next_buffer;
     track_buffer_.pop_front();
     last_output_buffer_timestamp_ = (*out_buffer)->GetDecodeTimestamp();
 
@@ -1338,6 +1404,15 @@ bool SourceBufferStream::UpdateVideoConfig(const VideoDecoderConfig& config) {
 void SourceBufferStream::CompleteConfigChange() {
   config_change_pending_ = false;
 
+  if (fade_in_buffer_) {
+    const std::vector<scoped_refptr<StreamParserBuffer> >& fade_out_preroll =
+        fade_in_buffer_->GetFadeOutPreroll();
+    current_config_index_ = fade_out_preroll_index_ < fade_out_preroll.size() ?
+        fade_out_preroll.at(fade_out_preroll_index_)->GetConfigId() :
+        fade_in_buffer_->GetConfigId();
+    return;
+  }
+
   if (!track_buffer_.empty()) {
     current_config_index_ = track_buffer_.front()->GetConfigId();
     return;
@@ -1858,7 +1933,13 @@ bool SourceBufferRange::HasNextBuffer() const {
 
 int SourceBufferRange::GetNextConfigId() const {
   DCHECK(HasNextBuffer());
-  return buffers_.at(next_buffer_index_)->GetConfigId();
+  const scoped_refptr<StreamParserBuffer>& next_buffer =
+      buffers_.at(next_buffer_index_);
+  // If the next buffer is an audio splice frame, the next effective config id
+  // comes from the first fade out preroll buffer.
+  return next_buffer->GetFadeOutPreroll().empty() ?
+      next_buffer->GetConfigId() :
+      next_buffer->GetFadeOutPreroll().at(0)->GetConfigId();
 }
 
 base::TimeDelta SourceBufferRange::GetNextTimestamp() const {