Update padding/alignment constants to match ffmpeg.

media/ffmpeg/ffmpeg_common.cc

Index: media/ffmpeg/ffmpeg_common.cc
diff --git a/media/ffmpeg/ffmpeg_common.cc b/media/ffmpeg/ffmpeg_common.cc
index 5b6ef7fe3c19c3df7b31ffb194240198bc3e6f81..ca82eadce55013bbb26e6f8ec4cf9f9573012f31 100644
--- a/media/ffmpeg/ffmpeg_common.cc
+++ b/media/ffmpeg/ffmpeg_common.cc
@@ -22,7 +22,7 @@ static_assert(DecoderBuffer::kPaddingSize >= FF_INPUT_BUFFER_PADDING_SIZE,
               "DecoderBuffer padding size does not fit ffmpeg requirement");
 
 // Alignment requirement by FFmpeg for input and output buffers. This need to
-// be updated to match FFmpeg when it changes.
+// be updated to match FFmpeg when it changes. See libavutil/mem.c.
 #if defined(ARCH_CPU_ARM_FAMILY)
 static const int kFFmpegBufferAddressAlignment = 16;
 #else
@@ -35,18 +35,21 @@ static_assert(
     DecoderBuffer::kAlignmentSize % kFFmpegBufferAddressAlignment == 0,
     "DecoderBuffer alignment size does not fit ffmpeg requirement");
 
-// Allows faster SIMD YUV convert. Also, FFmpeg overreads/-writes occasionally.
-// See video_get_buffer() in libavcodec/utils.c.
-static const int kFFmpegOutputBufferPaddingSize = 16;
-
-static_assert(VideoFrame::kFrameSizePadding >= kFFmpegOutputBufferPaddingSize,
-              "VideoFrame padding size does not fit ffmpeg requirement");
-
 static_assert(
     VideoFrame::kFrameAddressAlignment >= kFFmpegBufferAddressAlignment &&
     VideoFrame::kFrameAddressAlignment % kFFmpegBufferAddressAlignment == 0,
     "VideoFrame frame address alignment does not fit ffmpeg requirement");
 
+static_assert(
+    VideoFrame::kFrameSizeAlignment >= STRIDE_ALIGN &&
+    VideoFrame::kFrameSizeAlignment % STRIDE_ALIGN == 0,
+    "VideoFrame size alignment does not fit ffmpeg requirement");
+
+// Allows faster SIMD YUV convert. Also, FFmpeg overreads/-writes occasionally.
+// See video_get_buffer() and update_frame_pool() in libavcodec/utils.c
+static_assert(VideoFrame::kFrameSizePadding >= FRAME_PADDING,
+              "VideoFrame padding size does not fit ffmpeg requirement");
+
 static const AVRational kMicrosBase = { 1, base::Time::kMicrosecondsPerSecond };
 
 base::TimeDelta ConvertFromTimeBase(const AVRational& time_base,