I am using ffmpeg-python to convert an hevc mkv file to an h264 mp4. This is the relevant code:

ffmpeg.input(video_file).output(out_name, vcodec='libx264', **{'pix_fmt': 'yuv420p'}).run()

Yet after converting the file, the resulting mp4 will only play in certain media players. Here is the result of running ffprobe on the mp4:

ffprobe output

I know this should be possible, so does anyone have an idea of why it isn't playing in older/more standard media players?

  • 1
    Possibly, the 6 channels in the audio. Add the CLI option -ac 2 and check.
    – Gyan
    Oct 18, 2022 at 11:57
  • @Gyan Wow, this worked! I never would have even thought to try this! If you want to give this as an answer then I'll accept it. Thank you so much!
    – Bob Smith
    Oct 19, 2022 at 10:12

1 Answer 1


Legacy media players like Windows Media Player may be finicky about the files they will accept. In this case, it looks like the audio channel count of 6 is too high.

Add the CLI option -ac 2 and check.

  • To be clear, the "Movies & TV" app, which was added in Windows 10, also was not able to play the video with 6 audio channels. Either way, thanks a lot for the help :)
    – Bob Smith
    Oct 21, 2022 at 5:54

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