Support (E)AC3 passthrough

media/base/audio_splicer.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/base/audio_splicer.h"
 
 #include <stdint.h>
 #include <cstdlib>
 #include <deque>
 #include <utility>
@@ skipping 165 matching lines @@
         << "us, more than threshold of +/-"
         << AudioSplicer::kMaxTimeDeltaInMilliseconds
         << "ms. Expected timestamp is based on decoded frames and frame rate.";
     return false;
   }
 
   int frames_to_fill = 0;
   if (!delta.is_zero())
     frames_to_fill = output_timestamp_helper_.GetFramesToTarget(timestamp);
 
-  if (frames_to_fill == 0 || std::abs(frames_to_fill) < kMinGapSize) {
+  if (frames_to_fill == 0 || std::abs(frames_to_fill) < kMinGapSize ||

[DaleCurtis, 2016/11/01 23:05:13]

Raw formats should just skip the sanitizer entirely. Notably this is going to
break things like append window trimming in MSE. So authors will have to be very
careful to ensure they align their buffers correctly during streaming.
+chcunningham.

[AndyWu, 2016/11/04 18:04:24]

Sorry, I am not sure what to do. Should I move the change to line 154 or 164?

[chcunningham, 2016/11/11 19:14:28]

This whole file is now deleted. But Dale is right about append window trimming
(see use case: http://dalecurtis.github.io/llama-demo/index.html)

Append window trimming is achieved by discarding decoded frames in
audio_discard_helper. I'm not sure how you'll support this in a passthrough
scenario. 

[AndyWu, 2016/11/11 23:49:12]

Thanks a lot for the well written article from Dale.
We can still discard bitstream in terms of "compressed audio frame", which is
576 PCM frames in MP3. That is, dropping a complete AudioBuffer data should be
acceptable in passthrough mode.

+      input->sample_format() == kSampleFormatRaw) {
     AddOutputBuffer(input);
     return true;
   }
 
   if (frames_to_fill > 0) {
     LIMITED_MEDIA_LOG(DEBUG, media_log_, num_warning_logs_,
                       kMaxSanitizerWarningLogs)
         << "Audio splicer inserting silence for small gap of "
         << delta.InMicroseconds() << "us at time "
         << expected_timestamp.InMicroseconds() << "us.";
@@ skipping 354 matching lines @@
     AccurateTrimStart(frames_to_trim, remainder, output_ts_helper);
     CHECK(output_sanitizer_->AddInput(remainder));
   }
 
   // Transfer all remaining buffers out and reset once empty.
   CHECK(post_splice_sanitizer_->DrainInto(output_sanitizer_.get()));
   post_splice_sanitizer_->Reset();
 }
 
 }  // namespace media