Update padding/alignment constants to match ffmpeg.

media/base/video_frame.h

Index: media/base/video_frame.h
diff --git a/media/base/video_frame.h b/media/base/video_frame.h
index 80169cbe822990ca487fa5993d12bc2c5a7aa0d0..0158eab4e1838a1536b53e67b511897d8310f731 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -28,8 +28,10 @@ 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
   };