Optional filter specification for "ext" doesn't work

[realnc]

Videos that are provided only in "mp4" by YouTube break youtube-dl when using a filter specification such as:

$ youtube-dl -f 'bestvideo[ext=?webm]+bestaudio' -g https://www.youtube.com/watch?v=1UE2x2OcfxI
ERROR: requested format not available

I have [ext=?webm] stored as a default option, so that WebM is preferred, but if it doesn't exist (like in the video given in the example above), then H.264 video is OK. The point is that WebM should be preferred if both are available, but it shouldn't fail if WebM is not available, since the filter operator is =?, not just =.

In case it matters, the same thing happens with audio. Same error message if I try bestvideo+bestaudio[ext=?webm].

A workaround exists, but it can get rather long. For example, this doesn't work:

bestvideo[ext=?webm]+bestaudio[ext=?webm]

But the longer equivalent does work:

bestvideo[ext=webm]+bestaudio[ext=webm]/bestvideo[ext=mp4]+bestaudio[ext=webm]/bestvideo[ext=mp4]+bestaudio[ext=mp4]/bestvideo[ext=webm]+bestaudio[ext=mp4]

(The reason I prefer webm is because YouTube's H.264 encodes are lower quality compared to their VP9 encodes, even though the former has a higher bitrate compared to the latter.)

[phihag]

That's not how =? works. [ext=?webm] matches either webm or unset ext values, but all of the formats of the video have non-webm extensions.

[realnc]

Oh. Is that useful though? Shouldn't it mean "webm, and if that's not available, then whatever you would have picked instead."

The current behavior doesn't sound useful, or at least not as useful.

[yan12125]

@realnc You may want to try -f 'bestvideo[ext=webm]+bestaudio/bestvideo+bestaudio/best'.

[realnc]

@yan1212 As mentioned already, I'm using bestvideo[ext=webm]+bestaudio[ext=webm]/bestvideo[ext=mp4]+bestaudio[ext=webm]/bestvideo[ext=mp4]+bestaudio[ext=mp4]/bestvideo[ext=webm]+bestaudio[ext=mp4], which is kind of a monstrosity. But it that's how it's designed to be...

[yan12125]

FYI: Grouping in format filters is requested in #5242 and implemented in #6124. You may want to try it. I guess (bestvideo[ext=webm]/bestvideo[ext=mp4])+(bestaudio[ext=webm]/bestaudio[ext=mp4]) works the same as the previous filter.