Unnecessary transcoding of FLAC in FireFox.

[rechigo 364]

When trying to play back media containing a FLAC audio track in the latest version of FireFox (143.0.3) , Emby transcodes the FLAC to AAC despite Firefox's website stating all platforms can handle FLAC, and I am able to play the audio track of the media in question in the browser just fine.

Is there some sort of limitation that is forcing this conversion to take place? 

[Luke 42077]

Hi, there is no limitation. It is all based on what the browser reports as being supported.

[Lessaj 467]

I recall a post earlier this year that FLACs over a certain bitrate were being transcoded. Was an ffmpeg transcode log generated? It may have that detail in it.

[rechigo 364]

2 hours ago, Luke said:

Hi, there is no limitation. It is all based on what the browser reports as being supported.

So since the video is being direct streamed due to unsupported container (MKV), it is delivered to the client in the form of MPEGTS segments. MPEGTS does not support FLAC, hence the transcoding to AAC.

 

The good news here is that FINALLY firefox has implemented MKV support for H264/HEVC* after almost a decade.... MKV Support hasn't made its way to stable quite yet, but in nightly I am able to direct play FLAC audio in firefox nightly.

[Luke 42077]

4 minutes ago, rechigo said:

So since the video is being direct streamed due to unsupported container (MKV), it is delivered to the client in the form of MPEGTS segments. MPEGTS does not support FLAC, hence the transcoding to AAC.

 

The good news here is that FINALLY firefox has implemented MKV support for H264/HEVC* after almost a decade.... MKV Support hasn't made its way to stable quite yet, but in nightly I am able to direct play FLAC audio in firefox nightly.

OK if you can remind me once that hits firefox beta, I will test it out and see if we can enable it. Normally supported formats are auto-detected, but Chrome added mkv support many years ago without providing a way to detect support, so we had to just hardcode it.

[rechigo 364]

1 hour ago, Luke said:

OK if you can remind me once that hits firefox beta, I will test it out and see if we can enable it. Normally supported formats are auto-detected, but Chrome added mkv support many years ago without providing a way to detect support, so we had to just hardcode it.

Well that's the thing.... I was playing a FLAC+HEVC MKV through emby web in firefox nightly and it was direct playing... So Emby must be doing some sort of auto detection?

 

As of FF Beta 143 MKV support is not present... Will keep tabs on it periodically... According to FF release schedule, version 145 (currently nightly) becomes Beta on October 13th.

Edited October 9, 2025 by rechigo

[Luke 42077]

actually now that i recall, i did add some detection for mkv a long time ago even though there was no browser that was known to respond to it. 

so if what you're saying is true, then i guess we got lucky and the way they implemented it matches how we're checking for it.