Which file formats are most compatible with libre software / respecting of user freedom?

This page is under construction. Current status: formatted notes. Last edited: 2025-04-05.

Video

I should explain here why video is a bit complicated, what codecs, containers mean and give an overview of how it all fits together.

Container

Comparison of video container formats - wikipedia

From the comparison table, it seems that the most usuable container formats are matroska and ogg. webm is free as in free beer but google still holds the patents, I don't know if you can take the spec and modify it, don't know patent law well enough.

Therefore, we choose mkv.

Codecs

should make a performance comparison. from our survey, the most usuable libre formats are, ordered by recency:

we choose AV1 by far, it was chosen as the successor to VP9, the Videolan team have written a stellar performant software decoder for it (dav1d) and it is more performant than HVEC. If you want to be convinced, just listen to Jean-Baptiste Kempf talk about dav1d.

Audio in video files

Opus, it's the successor to Vorbis and it's the best libre audio format (very commonly used nowadays, in realtime video call software for instance).

Subtitles

Subtitle text formats

  1. WebVTT (HTML), based on SubRip, a little more advanced and standardized subtitle format for HTML5 video
  2. fallback to SRT if there is a problem, but I don't see how there would be.
  3. SubRip (SRT) seems widely supported, GPL license, seems to be made by the matroska people
  4. TTML

Subtitle image formats

VOBSUB usually found in dvd

Subtitle formats conclusion

We always prefer to use a text format over an image format for subtitles since text formats are easily editable (correct mistakes, easily collaborate on subtitles).
Our text format of choice is WebVTT as it is based on the universal SubRip and is a W3C standard and is the standard for HTML5 video subtitles.
Our image format of choice is VOBSUB. It is very widespread.
When ripping a dvd the subtitle format will usually be VOBSUB, and since we can't yet convert subtitles from image to text (maybe this exists but certainly not entirely reliable, not worth the trouble), we shall keep VOBSUB when we have to.

Video formats conclusion

mkv container with AV1 video, Opus audio and WebVTT subtitles for text subtitles, and fallback to VOBSUB if existing subtitles were in an image format.