Converting audio along with video after download

[ankenyr]

• I've verified and I assure that I'm running youtube-dl 2017.06.12
• At least skimmed through README and most notably FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones

What is the purpose of your issue?

• Question

Right now I have something akin to the following for my options

ydl_opts = {
  'noprogress': True,
  'ignoreerrors': True,
  'restrictfilenames': True,
  'nooverwrites': True,
  'writeinfojson': True,
  'writedescription': True,
  'writesubtitles': True,
  'subtitleslangs': ['en'],
  'download_archive': 'one_off_archive.txt',
  'outtmpl': '',
  'postprocessors': [
    {
      'key': 'FFmpegVideoConvertor',
      'preferedformat': 'mkv',
    },
  ],
  'logger': MyLogger(log_file),
}

This will download videos and convert to mkv but the audio is left alone. I would like to if possible convert it to AAC. It seems like this should be possible and obvious but for the life of me I cannot figure it out. Looking at the code I see there is a post processor to extract audio but not to convert the audio itself. (https://github.com/rg3/youtube-dl/blob/master/youtube_dl/postprocessor/ffmpeg.py#L218)

Is this just a feature that has not been implemented? Is it something that would be desirable? Happy to work on this myself and form a PR but would like some help knowing if I am barking up the right tree so to say.

[ticky]

I’d love this, too! Most of the time it’s going to be more useful for me to have mp4 output even if the audio originally came from an opus stream! 😄

[ankenyr]

Glad to hear others would want this also. I explored a bit more, there is the ExecAfterDownload but that seems to have it's own problems. Adding the following to the postprocessors

    {
      'key': 'ExecAfterDownload',
      'exec_cmd': "ffmpeg -i {} -acodec mp3 -vcodec copy out.mkv"
    },

results in an error stating that there is an invalid argument. It seems ffmpeg does not like the quotes put around the file path.