VideoWriter fallback when using H264

[Gartarr]

Hello. I get following error when using VideoWriter with FourCC: H264:
OpenCV: FFMPEG: tag 0x34363248/'H264' is not supported with codec id 27 and format 'mp4 / MP4 (MPEG-4 Part 14)'
OpenCV: FFMPEG: fallback to use tag 0x31637661/'avc1'

_videoWriter = new VideoWriter(Path.Combine("CreatedFiles", _fileName), backend_idx,
    VideoWriter.Fourcc('H', '2', '6', '4'), 30, HD_IMAGE_SIZE, true);

Where backend_idx corresponds to FFMPEG