Reducing the IPC latency for MSE video decoding

media/base/android/media_decoder_job.h

 // Copyright 2013 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.
 
 #ifndef MEDIA_BASE_ANDROID_MEDIA_DECODER_JOB_H_
 #define MEDIA_BASE_ANDROID_MEDIA_DECODER_JOB_H_
 
 #include "base/callback.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "media/base/android/demuxer_stream_player_params.h"
 #include "media/base/android/media_codec_bridge.h"
 
 namespace base {
 class SingleThreadTaskRunner;
 }
 
 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 {
     inline void operator()(MediaDecoderJob* ptr) const { ptr->Release(); }
   };
 
   // Callback when a decoder job finishes its work. Args: whether decode
   // finished successfully, presentation time, audio output bytes.
   // If the presentation time is equal to kNoTimestamp(), the decoder job
   // skipped rendering of the decoded output and the callback target should
@@ skipping 37 matching lines @@
   // Flush the decoder.
   void Flush();
 
   // Enter prerolling state. The job must not currently be decoding.
   void BeginPrerolling(const base::TimeDelta& preroll_timestamp);
 
   bool prerolling() const { return prerolling_; }
 
   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,
       MediaCodecBridge* media_codec_bridge,
       const base::Closure& request_data_cb);
 
   // Release the output buffer at index |output_buffer_index| and render it if
   // |render_output| is true. Upon completion, |callback| will be called.
   virtual void ReleaseOutputBuffer(
       int output_buffer_index,
@@ skipping 11 matching lines @@
 
   MediaCodecStatus QueueInputBuffer(const AccessUnit& unit);
 
   // Returns true if this object has data to decode.
   bool HasData() const;
 
   // Initiates a request for more data.
   // |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.

 
   // Helper function to decoder data on |thread_|. |unit| contains all the data
   // to be decoded. |start_time_ticks| and |start_presentation_timestamp|
   // represent the system time and the presentation timestamp when the first
   // frame is rendered. We use these information to estimate when the current
   // frame should be rendered. If |needs_flush| is true, codec needs to be
   // flushed at the beginning of this call.
   void DecodeInternal(const AccessUnit& unit,
                       const base::TimeTicks& start_time_ticks,
                       const base::TimeDelta& start_presentation_timestamp,
                       bool needs_flush,
                       const DecoderCallback& callback);
 
   // Called on the UI thread to indicate that one decode cycle has completed.
   // Completes any pending job destruction or any pending decode stop. If
   // destruction was not pending, passes its arguments to |decode_cb_|.
   void OnDecodeCompleted(MediaCodecStatus status,
                          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_;
 
   // The task runner that decoder job runs on.
   scoped_refptr<base::SingleThreadTaskRunner> decoder_task_runner_;
 
   // The media codec bridge used for decoding. Owned by derived class.
   // NOTE: This MUST NOT be accessed in the destructor.
   MediaCodecBridge* media_codec_bridge_;
 
@@ skipping 32 matching lines @@
 
   // Callback used to request more data.
   base::Closure request_data_cb_;
 
   // Callback to run when new data has been received.
   base::Closure on_data_received_cb_;
 
   // 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.
+  // 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];
 
-  // Data received over IPC from last RequestData() operation.
-  DemuxerData received_data_;
+  // 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.
   int input_buf_index_;
 
   bool stop_decode_pending_;
 
   // Indicates that this object should be destroyed once the current
   // Decode() has completed. This gets set when Release() gets called
   // 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);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_ANDROID_MEDIA_DECODER_JOB_H_