[webcodecs] Fix the buffer size issue during H.264 conversion.

Between AnnexB and AVCC bitstream formats, the start code length and
the nal size length can be different. Here to retry the conversion
if the output buffer size is too small.

Bug: 1119636
Change-Id: I517e81ef152a19b577fa04a60297f1dc35b1aeb7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2508998Reviewed-by: Dan Sanders <sandersd@chromium.org>
Reviewed-by: Eugene Zemtsov <eugene@chromium.org>
Commit-Queue: Chunbo Hua <chunbo.hua@intel.com>
Cr-Commit-Position: refs/heads/master@{#822960}

media/video/video_encode_accelerator_adapter.cc

@@ -366,6 +366,19 @@ void VideoEncodeAcceleratorAdapter::BitstreamBufferReady(
         h264_converter_->ConvertChunk(base::span<uint8_t>(src, result.size),
                                       base::span<uint8_t>(dst.get(), dst_size),
                                       &config_changed, &actual_output_size);
+    if (status.code() == StatusCode::kH264BufferTooSmall) {
+      // Between AnnexB and AVCC bitstream formats, the start code length and
+      // the nal size length can be different. See H.264 specification at
+      // http://www.itu.int/rec/T-REC-H.264. Retry the conversion if the output
+      // buffer size is too small.
+      dst_size = actual_output_size;
+      dst.reset(new uint8_t[dst_size]);
+      status = h264_converter_->ConvertChunk(
+          base::span<uint8_t>(src, result.size),
+          base::span<uint8_t>(dst.get(), dst_size), &config_changed,
+          &actual_output_size);
+    }
+
     if (!status.is_ok()) {
       LOG(ERROR) << status.message();
       NotifyError(VideoEncodeAccelerator::kPlatformFailureError);