Simplify AudioSplicer logic which slots buffers before or after a splice point.

media/base/audio_splicer.cc

Index: media/base/audio_splicer.cc
diff --git a/media/base/audio_splicer.cc b/media/base/audio_splicer.cc
index 29649bc9ce8e80f33189771f570d4834f9367d95..eac1c4924f6d121078e1cbb268d6e7aecaaa5320 100644
--- a/media/base/audio_splicer.cc
+++ b/media/base/audio_splicer.cc
@@ -91,9 +91,6 @@ class AudioStreamSanitizer {
   // Returns the total frame count of all buffers available for output.
   int GetFrameCount() const;
 
-  // Returns the duration of all buffers added to the output queue thus far.
-  base::TimeDelta GetDuration() const;
-
   const AudioTimestampHelper& timestamp_helper() {
     return output_timestamp_helper_;
   }
@@ -243,12 +240,6 @@ int AudioStreamSanitizer::GetFrameCount() const {
   return frame_count;
 }
 
-base::TimeDelta AudioStreamSanitizer::GetDuration() const {
-  DCHECK(output_timestamp_helper_.base_timestamp() != kNoTimestamp());
-  return output_timestamp_helper_.GetTimestamp() -
-         output_timestamp_helper_.base_timestamp();
-}
-
 bool AudioStreamSanitizer::DrainInto(AudioStreamSanitizer* output) {
   while (HasNextBuffer()) {
     if (!output->AddInput(GetNextBuffer()))
@@ -264,7 +255,8 @@ AudioSplicer::AudioSplicer(int samples_per_second)
       max_splice_end_timestamp_(kNoTimestamp()),
       output_sanitizer_(new AudioStreamSanitizer(samples_per_second)),
       pre_splice_sanitizer_(new AudioStreamSanitizer(samples_per_second)),
-      post_splice_sanitizer_(new AudioStreamSanitizer(samples_per_second)) {}
+      post_splice_sanitizer_(new AudioStreamSanitizer(samples_per_second)),
+      have_all_pre_splice_buffers_(false) {}
 
 AudioSplicer::~AudioSplicer() {}
 
@@ -272,6 +264,7 @@ void AudioSplicer::Reset() {
   output_sanitizer_->Reset();
   pre_splice_sanitizer_->Reset();
   post_splice_sanitizer_->Reset();
+  have_all_pre_splice_buffers_ = false;
   reset_splice_timestamps();
 }
 
@@ -286,17 +279,8 @@ bool AudioSplicer::AddInput(const scoped_refptr<AudioBuffer>& input) {
   const AudioTimestampHelper& output_ts_helper =
       output_sanitizer_->timestamp_helper();
 
-  if (!post_splice_sanitizer_->HasNextBuffer()) {
-    // Due to inaccurate demuxer timestamps a splice may have been incorrectly
-    // marked such that the "pre splice buffers" were all entirely before the
-    // splice point.  Here we check for end of stream or buffers which couldn't
-    // possibly be part of the splice.
-    if (input->end_of_stream() ||
-        input->timestamp() >= max_splice_end_timestamp_) {
-      CHECK(pre_splice_sanitizer_->DrainInto(output_sanitizer_.get()));
-      reset_splice_timestamps();
-      return output_sanitizer_->AddInput(input);
-    }
+  if (!have_all_pre_splice_buffers_) {
+    DCHECK(!input->end_of_stream());
 
     // If the provided buffer is entirely before the splice point it can also be
     // added to the output queue.
@@ -314,24 +298,13 @@ bool AudioSplicer::AddInput(const scoped_refptr<AudioBuffer>& input) {
           output_ts_helper.frame_count(), output_ts_helper.base_timestamp());
     }
 
-    // The first overlapping buffer is expected to have a timestamp of exactly
-    // |splice_timestamp_|.  Until that timestamp is seen, all buffers go into
-    // |pre_splice_sanitizer_|.
-    if (!pre_splice_sanitizer_->HasNextBuffer() ||
-        input->timestamp() != splice_timestamp_) {
-      return pre_splice_sanitizer_->AddInput(input);
-    }
-
-    // We've received the first overlapping buffer.
-  } else if (!input->end_of_stream() &&
-             input->timestamp() == splice_timestamp_) {
-    // In this case we accidentally put a pre splice buffer in the post splice
-    // sanitizer, so we need to recover by transferring all current post splice
-    // buffers into the pre splice sanitizer and continuing with the splice.
-    post_splice_sanitizer_->DrainInto(pre_splice_sanitizer_.get());
-    post_splice_sanitizer_->Reset();
+    return pre_splice_sanitizer_->AddInput(input);
   }
 
+  // The first post splice buffer is expected to match |splice_timestamp_|.
+  if (!post_splice_sanitizer_->HasNextBuffer())
+    DCHECK(splice_timestamp_ == input->timestamp());
+
   // At this point we have all the fade out preroll buffers from the decoder.
   // We now need to wait until we have enough data to perform the crossfade (or
   // we receive an end of stream).
@@ -356,12 +329,11 @@ bool AudioSplicer::AddInput(const scoped_refptr<AudioBuffer>& input) {
     return true;
   }
 
-  // Since it's possible that a pre splice buffer after the first might have its
-  // timestamp fuzzed to be |splice_timestamp_| we need to always wait until we
-  // have seen all possible post splice buffers to ensure we didn't mistakenly
-  // put a pre splice buffer into the post splice sanitizer.
-  if (!input->end_of_stream() && input->timestamp() < max_splice_end_timestamp_)
+  // Wait until we have enough data to crossfade or end of stream.
+  if (!input->end_of_stream() &&
+      input->timestamp() + input->duration() < max_splice_end_timestamp_) {
     return true;
+  }
 
   scoped_refptr<AudioBuffer> crossfade_buffer;
   scoped_ptr<AudioBus> pre_splice =
@@ -385,7 +357,13 @@ scoped_refptr<AudioBuffer> AudioSplicer::GetNextBuffer() {
 }
 
 void AudioSplicer::SetSpliceTimestamp(base::TimeDelta splice_timestamp) {
-  DCHECK(splice_timestamp != kNoTimestamp());
+  if (splice_timestamp == kNoTimestamp()) {
+    DCHECK(splice_timestamp_ != kNoTimestamp());
+    DCHECK(!have_all_pre_splice_buffers_);
+    have_all_pre_splice_buffers_ = true;
+    return;
+  }
+
   if (splice_timestamp_ == splice_timestamp)
     return;
 
@@ -398,6 +376,7 @@ void AudioSplicer::SetSpliceTimestamp(base::TimeDelta splice_timestamp) {
   max_splice_end_timestamp_ = splice_timestamp_ + max_crossfade_duration_;
   pre_splice_sanitizer_->Reset();
   post_splice_sanitizer_->Reset();
+  have_all_pre_splice_buffers_ = false;
 }
 
 scoped_ptr<AudioBus> AudioSplicer::ExtractCrossfadeFromPreSplice(