Reducing the IPC latency for MSE video decoding

media/base/android/media_decoder_job.h

Index: media/base/android/media_decoder_job.h
diff --git a/media/base/android/media_decoder_job.h b/media/base/android/media_decoder_job.h
index 286d27cf75b5c60251085d7000764736f7a8fd6a..4d523a015e21b0e8f37eba96970ffedf9075c827 100644
--- a/media/base/android/media_decoder_job.h
+++ b/media/base/android/media_decoder_job.h
@@ -19,6 +19,9 @@ namespace media {
 
 // Class for managing all the decoding tasks. Each decoding task will be posted
 // onto the same thread. The thread will be stopped once Stop() is called.
+// Data is stored in 2 chunks. When new data arrives, it is always stored in
+// an inactive chunk. And when the current active chunk becomes empty, a new
+// data request will be sent to the renderer.
 class MediaDecoderJob {
  public:
   struct Deleter {
@@ -76,6 +79,10 @@ class MediaDecoderJob {
 
   bool is_decoding() const { return !decode_cb_.is_null(); }
 
+  bool is_requesting_demuxer_data() const {
+    return is_requesting_demuxer_data_;
+  }
+
  protected:
   MediaDecoderJob(
       const scoped_refptr<base::SingleThreadTaskRunner>& decoder_task_runner,
@@ -107,8 +114,8 @@ class MediaDecoderJob {
   // |done_cb| is called when more data is available in |received_data_|.
   void RequestData(const base::Closure& done_cb);
 
-  // Posts a task to start decoding the next access unit in |received_data_|.
-  void DecodeNextAccessUnit(
+  // Posts a task to start decoding the current access unit in |received_data_|.
+  void DecodeCurrentAccessUnit(
       const base::TimeTicks& start_time_ticks,
       const base::TimeDelta& start_presentation_timestamp);

[wolenetz, 2014/03/17 19:51:00]

nit: const & for TimeDelta is not current style. Underlying data is just an
int64.

[qinmin, 2014/03/18 18:58:58]

Done.

 
@@ -131,6 +138,18 @@ class MediaDecoderJob {
                          const base::TimeDelta& presentation_timestamp,
                          size_t audio_output_bytes);
 
+  // Helper function to get the current access unit that is being decoded.
+  const AccessUnit& CurrentAccessUnit() const;
+
+  // Check whether a chunk is empty.

[wolenetz, 2014/03/17 19:51:00]

nit: Describe meaning of |current_chunk|.

[qinmin, 2014/03/18 18:58:58]

Done.

+  bool IsDemuxerDataEmpty(bool current_chunk) const;
+
+  // Clearn all the received data.
+  void ClearData();
+
+  // Request new data for the current chunk if it runs out of data.
+  void RequestCurrentChunkIfEmpty();
+
   // The UI message loop where callbacks should be dispatched.
   scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner_;
 
@@ -183,11 +202,19 @@ class MediaDecoderJob {
   // Callback to run when the current Decode() operation completes.
   DecoderCallback decode_cb_;
 
-  // The current access unit being processed.
-  size_t access_unit_index_;
-
   // Data received over IPC from last RequestData() operation.
-  DemuxerData received_data_;
+  // We keep 2 chunks at the same time to reduce the IPC latency between chunks.
+  // If data inside the current chunk are all decoded, we will request a new
+  // chunk from the demuxer and swap the current chunk with the other one.
+  // New data will always be stored in the other chunk since the current
+  // one may be still in use.
+  DemuxerData received_data_[2];
+
+  // Index to the current data chunk that is being decoded.
+  size_t current_demuxer_data_index_;
+
+  // Index to the access unit inside each data chunk that is being decoded.
+  size_t access_unit_index_[2];
 
   // The index of input buffer that can be used by QueueInputBuffer().
   // If the index is uninitialized or invalid, it must be -1.
@@ -200,6 +227,13 @@ class MediaDecoderJob {
   // while there is a decode in progress.
   bool destroy_pending_;
 
+  // Indicates whether the decoder is in the middle of requesting new data.
+  bool is_requesting_demuxer_data_;
+
+  // Indicates whether the incoming data should be ignored.
+  bool is_incoming_data_invalid_;
+
+  friend class MediaSourcePlayerTest;
   DISALLOW_IMPLICIT_CONSTRUCTORS(MediaDecoderJob);
 };