Select the best quality with a unified extension

[stdedos]

Checklist

• I'm reporting a feature request
• I've verified that I'm running youtube-dl version 2020.09.20
• I've searched the bugtracker for similar feature requests including closed ones (for year 2020 - my search "https://github.com/ytdl-org/youtube-dl/issues?page=3&q=Requested+formats+are+incompatible+for+merge+and+will+be+merged+into+mkv" gives 11 pages)

#26810, #25089

Description

Using the bare-bones command line, sometimes it ends up with

youtube-dl/youtube_dl/YoutubeDL.py

Line 1903 in 7947a1f

'Requested formats are incompatible for merge and will be merged into mkv.')

this message. I wonder if there could be a way to get "almost the best video quality" (be that e.g. webm or mp4), without resorting to mkv, and without hardcoding what to get explicitly.

I don't want to use mkv if I will get something like "just 5% better quality".

[s104346]

# Download best mp4 format available or any other best if no mp4 available
$ youtube-dl -f "bestvideo[ext=mp4]+bestaudio[ext=m4a]/best[ext=mp4]/best"

from https://github.com/ytdl-org/youtube-dl#format-selection

[stdedos]

From what I wrote:

"almost the best video quality" (be that e.g. webm or mp4), [...], and without hardcoding what to get explicitly

[ilike2burnthing]

--merge-output-format mp4
https://github.com/ytdl-org/youtube-dl#video-format-options

[stdedos]

I guess it is not clear enough:

If the webm gives 4K, and mp4 gives 1080p, I obviously want webm (even with a 5% sub-par mp4 track).
However, if the video is "just" 5% better than the mp4 format, I prefer mp4 format.

However, I don't want to "explicitly" decide/block one format over the other one.

[ilike2burnthing]

There isn't much that .mp4 containers can't typically handle but .webm can (just Vorbis audio I think) - https://en.wikipedia.org/wiki/Comparison_of_video_container_formats

--merge-output-format mp4 works fine merging .mp4 video with .webm (Opus) audio, or .webm video (VP9) with .webm audio (Opus) from YouTube (just tested).