Firefox transcodes when it can direct play

[billcw 2]

Now that Firefox finally supports MKV, I have been doing some experimenting.  Running 4.9.5.0 with Firefox 151, if transcoding is enabled for the user, Emby transcodes compatible video and audio streams.  If I disable transcoding, then Emby direct plays the file just fine.

MKV file with transcoding enabled:

 

The same file with transcoding disabled:

In my case, having transcoding disabled is fine, but this could probably be improved.

[Luke 42887]

Hi, the reason is indicated in your first screenshot.

[billcw 2]

Well, the only difference that I see is the "selecting secondary audio track" bit, but it uses the same audio track in either case.

[Luke 42887]

OK so for this video you're getting lucky with this particular file but normally when a file has multiple audio tracks, firefox will auto pick the first track listed, and if you select anything other than that, then the only way we can play that track is via transcoding.

[billcw 2]

Ah, I get it now (with a little more experimentation).  With transcoding disabled, it only plays one audio track, regardless of what I select.  In this case, there is an AC3 track, then an Opus stereo track, and then an Opus commentary track.  Regardless of what audio selection I make in Emby, it uses the Opus stereo track, I guess because that is the first compatible track.  That actually works very well for my needs and potentially saves me from having to continue to generate stripped down WEBM files just for Firefox.  Thanks!