Update padding/alignment constants to match ffmpeg.

media/base/video_frame.h

 // 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.
 
 #ifndef MEDIA_BASE_VIDEO_FRAME_H_
 #define MEDIA_BASE_VIDEO_FRAME_H_
 
 #include <vector>
 
 #include "base/callback.h"
@@ skipping 10 matching lines @@
 #if defined(OS_MACOSX)
 #include <CoreVideo/CVPixelBuffer.h>
 #include "base/mac/scoped_cftyperef.h"
 #endif
 
 namespace media {
 
 class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
  public:
   enum {
-    kFrameSizeAlignment = 16,
-    kFrameSizePadding = 16,
+    // These values are chosen according to like values in FFmpeg. See static

[DaleCurtis, 2015/08/11 00:31:30]

Hmm, I wonder if we should instead add a constructor so that ffmpeg frames can
specify the right stride and such, but normal frames don't waste as much memory.

[miu, 2015/08/11 02:53:55]

+1.  This approach wastes memory for the non-ffmpeg producers of VideoFrames. 
Actually, the existing approach (16-byte alignment) also wastes memory.  But,
this CL proposes to waste more.  ;-)

Can FFMPEG specify the alignment- and padding-adjusted coded size using this
ctor:
https://code.google.com/p/chromium/codesearch#chromium/src/media/base/video_f...

Also, it feels like we've made a huge mistake [in the past], in that
VideoFrame::CreateFrame() can create a frame with a larger coded size than what
was provided.  There are plenty of use cases (e.g., HW codecs) where an EXACT
coded size is required.  FWICT, it just so happens that 16-byte alignment works
for everything right now.

+    // asserts in ffmpeg_common.
+    kFrameSizeAlignment = 32,
+    kFrameSizePadding = 47,
     kFrameAddressAlignment = 32
   };
 
   enum {
     kMaxPlanes = 4,
 
     kYPlane = 0,
     kARGBPlane = kYPlane,
     kUPlane = 1,
     kUVPlane = kUPlane,
@@ skipping 433 matching lines @@
   uint32 release_sync_point_;
 
   VideoFrameMetadata metadata_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(VideoFrame);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_FRAME_H_