Add support for partial append window end trimming.

media/base/audio_discard_helper.cc

Index: media/base/audio_discard_helper.cc
diff --git a/media/base/audio_discard_helper.cc b/media/base/audio_discard_helper.cc
index 303ee79f0cc40d8fbe4ced96d8b123c2f7ffa84b..bde71451b6497559dacbdcfeb2498042616694fa 100644
--- a/media/base/audio_discard_helper.cc
+++ b/media/base/audio_discard_helper.cc
@@ -29,7 +29,8 @@ AudioDiscardHelper::AudioDiscardHelper(int sample_rate, size_t decoder_delay)
       timestamp_helper_(sample_rate_),
       discard_frames_(0),
       last_input_timestamp_(kNoTimestamp()),
-      delayed_discard_(false) {
+      delayed_discard_(false),
+      delayed_end_discard_(0) {
   DCHECK_GT(sample_rate_, 0);
 }
 
@@ -99,6 +100,9 @@ bool AudioDiscardHelper::ProcessBuffers(
     const size_t frames_to_discard = std::min(discard_frames_, decoded_frames);
     discard_frames_ -= frames_to_discard;
 
+    DVLOG(1) << "Initial discard of " << frames_to_discard << " out of "
+             << decoded_frames << " frames.";
+
     // If everything would be discarded, indicate a new buffer is required.
     if (frames_to_discard == decoded_frames) {
       // For simplicity disallow cases where a buffer with discard padding is
@@ -112,6 +116,24 @@ bool AudioDiscardHelper::ProcessBuffers(
     decoded_buffer->TrimStart(frames_to_discard);
   }
 
+  // Process any delayed end discard from the previous buffer.
+  if (delayed_end_discard_ > 0) {
+    DCHECK_GT(decoder_delay_, 0u);
+    DCHECK_LT(delayed_end_discard_, decoder_delay_);
+
+    const size_t decoded_frames = decoded_buffer->frame_count();
+    const size_t frames_to_discard = decoder_delay_ - delayed_end_discard_;
+    DCHECK_LT(frames_to_discard, decoded_frames);
+
+    DVLOG(1) << "Delayed end discard of " << frames_to_discard << " out of "
+             << decoded_frames << " frames starting at "
+             << delayed_end_discard_;
+
+    decoded_buffer->TrimRange(delayed_end_discard_,
+                              delayed_end_discard_ + frames_to_discard);
+    delayed_end_discard_ = 0;
+  }
+
   // Handle front discard padding.
   if (current_discard_padding.first > base::TimeDelta()) {
     const size_t decoded_frames = decoded_buffer->frame_count();
@@ -153,6 +175,9 @@ bool AudioDiscardHelper::ProcessBuffers(
     DCHECK(!discard_frames_);
     discard_frames_ = start_frames_to_discard - frames_to_discard;
 
+    DVLOG(1) << "Front discard of " << frames_to_discard << " out of "
+             << decoded_frames << " frames starting at " << discard_start;
+
     // If everything would be discarded, indicate a new buffer is required.
     if (frames_to_discard == decoded_frames) {
       // The buffer should not have been marked with end discard if the front
@@ -168,24 +193,42 @@ bool AudioDiscardHelper::ProcessBuffers(
 
   // Handle end discard padding.
   if (current_discard_padding.second > base::TimeDelta()) {
-    // Limit end discarding to when there is no |decoder_delay_|, otherwise it's
-    // non-trivial determining where to start discarding end frames.
-    CHECK(!decoder_delay_);
-
     const size_t decoded_frames = decoded_buffer->frame_count();
-    const size_t end_frames_to_discard =
+    size_t end_frames_to_discard =
         TimeDeltaToFrames(current_discard_padding.second);
 
+    if (decoder_delay_) {
+      // Delayed end discard only works if the decoder delay is less than a
+      // single buffer.
+      DCHECK_LT(decoder_delay_, original_frame_count);
+
+      // If the discard is >= the decoder delay, trim everything we can off the
+      // end of this buffer and the rest from the start of the next.
+      if (end_frames_to_discard >= decoder_delay_) {
+        DCHECK(!discard_frames_);
+        discard_frames_ = decoder_delay_;
+        end_frames_to_discard -= decoder_delay_;
+      } else {
+        delayed_end_discard_ = decoder_delay_ - end_frames_to_discard;

[acolwell GONE FROM CHROMIUM, 2014/07/24 19:22:14]

Can you just store end_frames_to_discard here and then rework the TrimRange()
computation in ProcessBuffers(). ISTM that would be easier to understand and
make the comment for this member variable less confusing. IIUC this is just
delaying the end discard amount until we receive the next buffer.

[DaleCurtis, 2014/07/29 01:35:09]

Done.

+        end_frames_to_discard = 0;
+      }
+    }
+
     if (end_frames_to_discard > decoded_frames) {
       DLOG(ERROR) << "Encountered invalid discard padding value.";
       return false;
     }
 
-    // If everything would be discarded, indicate a new buffer is required.
-    if (end_frames_to_discard == decoded_frames)
-      return false;
+    if (end_frames_to_discard > 0) {
+      DVLOG(1) << "End discard of " << end_frames_to_discard << " out of "
+               << decoded_frames;
+
+      // If everything would be discarded, indicate a new buffer is required.
+      if (end_frames_to_discard == decoded_frames)
+        return false;
 
-    decoded_buffer->TrimEnd(end_frames_to_discard);
+      decoded_buffer->TrimEnd(end_frames_to_discard);
+    }
   } else {
     DCHECK(current_discard_padding.second == base::TimeDelta());
   }