How youtube-dl extracts (knows) frames per secont (fps) from Youtube video?

[cristalix]

Hi, this is not an issue, this is a question:

How youtube-dl knows which video format (possible video link) has frames per second (fps)? How it does get the info?

In _formats array, there's no fps col, or, better say, just few formats has fps defined: 298, 299, 302, 303, 308, 315 (60 fps). In final json, some video formats has defined fps (format 278 has 13 fps, format 242 has 25 fps) and some has empty fps value.

I found out this piece of code:

  more_fields = {
      'filesize': int_or_none(url_data.get('clen', [None])[0]),
      'tbr': float_or_none(url_data.get('bitrate', [None])[0], 1000),
      'width': width,
      'height': height,
      'fps': int_or_none(url_data.get('fps', [None])[0]),
      'format_note': url_data.get('quality_label', [None])[0] or url_data.get('quality', [None])[0],
  }

Can somebody explain me how youtube-dl extract info about number of video frames?

[yan12125]

Two places:

1. _formats table
2. YouTube provided metadata. Usually they can be found on the webpage

[cristalix]

What do you think under "Youtube provide metadata" in this case? On which webpage? May you be please more specific?

[yan12125]

In most cases the info is in https://www.youtube.com/watch?v=[video_id]&gl=US&hl=en&has_verified=1&bpctr=9999999999. In some cases they are in DASH manifests. URLs to DASH manifests are dynamically generated by YouTube. Use --dump-pages to get real URLs for them.

[cristalix]

OK, still pretty technical answer but I helped me to make everything clean. Thank you!