Replicate FFmpeg's video frame allocation strategy.

media/filters/ffmpeg_video_decoder.cc

Index: media/filters/ffmpeg_video_decoder.cc
diff --git a/media/filters/ffmpeg_video_decoder.cc b/media/filters/ffmpeg_video_decoder.cc
index 12980c1b83c8c7c28846f7fdc1d2e072bd9d464c..bc2346ddf8843526fde8ae980e847488e7ba0b13 100644
--- a/media/filters/ffmpeg_video_decoder.cc
+++ b/media/filters/ffmpeg_video_decoder.cc
@@ -72,8 +72,8 @@ int FFmpegVideoDecoder::GetVideoBuffer(AVCodecContext* codec_context,
          format == VideoFrame::YV12J);
 
   gfx::Size size(codec_context->width, codec_context->height);
-  int ret;
-  if ((ret = av_image_check_size(size.width(), size.height(), 0, NULL)) < 0)
+  const int ret = av_image_check_size(size.width(), size.height(), 0, NULL);
+  if (ret < 0)
     return ret;
 
   gfx::Size natural_size;
@@ -85,12 +85,22 @@ int FFmpegVideoDecoder::GetVideoBuffer(AVCodecContext* codec_context,
     natural_size = config_.natural_size();
   }
 
-  if (!VideoFrame::IsValidConfig(format, size, gfx::Rect(size), natural_size))
+  // FFmpeg has specific requirements on the allocation size of the frame.  The
+  // following logic replicates FFmpeg's allocation strategy to ensure buffers
+  // are not overread / overwritten.  See ff_init_buffer_info() for details.
+  //
+  // When lowres is non-zero, dimensions should be divided by 2^(lowres), but
+  // since we don't use this, just DCHECK that it's zero.
+  DCHECK_EQ(codec_context->lowres, 0);
+  gfx::Size coded_size(std::max(size.width(), codec_context->coded_width),
+                       std::max(size.height(), codec_context->coded_height));
+
+  if (!VideoFrame::IsValidConfig(
+          format, coded_size, gfx::Rect(size), natural_size))
     return AVERROR(EINVAL);
 
-  scoped_refptr<VideoFrame> video_frame =
-      frame_pool_.CreateFrame(format, size, gfx::Rect(size),
-                              natural_size, kNoTimestamp());
+  scoped_refptr<VideoFrame> video_frame = frame_pool_.CreateFrame(
+      format, coded_size, gfx::Rect(size), natural_size, kNoTimestamp());
 
   for (int i = 0; i < 3; i++) {
     frame->base[i] = video_frame->data(i);
@@ -101,8 +111,8 @@ int FFmpegVideoDecoder::GetVideoBuffer(AVCodecContext* codec_context,
   frame->opaque = NULL;
   video_frame.swap(reinterpret_cast<VideoFrame**>(&frame->opaque));
   frame->type = FF_BUFFER_TYPE_USER;
-  frame->width = codec_context->width;
-  frame->height = codec_context->height;
+  frame->width = coded_size.width();
+  frame->height = coded_size.height();
   frame->format = codec_context->pix_fmt;
 
   return 0;