Browser support for .mkv videos

[Kurami32]

Description
The .mkv videos don't play on v0.8.5 in Firefox and Firefox-based browsers. On previous versions was playing normally (or at least I remember that...)

Expected behaviour
Play the videos.

What is happening instead?
The videos don't play.

Additional context

• I tried on desktop and mobile (both firefox).
• The thumbnails and the motion preview of the video is working.
• The metadata of the .mkv video is working too, I can see that is detected enabling debugMedia on config file.

Output:

filebrowser  | ffmpeg version 8.0 Copyright (c) 2000-2025 the FFmpeg developers
filebrowser  |   built with gcc 14.2.0 (Alpine 14.2.0)
filebrowser  |   configuration: --pkg-config-flags=--static --extra-cflags='-static-libgcc -fno-strict-overflow -fPIC' --extra-cxxflags='-static-libgcc -fno-strict-overflow -fPIC' --extra-ldexeflags='-fPIE -static-pie' --extra-libs='-lm -fopenmp' --enable-small --enable-openssl --disable-shared --disable-ffplay --enable-static --enable-gpl --enable-libvpl --enable-libvorbis --enable-version3 --enable-libzimg --enable-fontconfig --enable-gray --enable-iconv --enable-lcms2 --enable-libaom --enable-libwebp --enable-libxml2 --enable-libdav1d --enable-libass --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-libsoxr --enable-libopenjpeg --enable-libsnappy --enable-libvpx
filebrowser  |   libavutil      60.  8.100 / 60.  8.100
filebrowser  |   libavcodec     62. 11.100 / 62. 11.100
filebrowser  |   libavformat    62.  3.100 / 62.  3.100
filebrowser  |   libavdevice    62.  1.100 / 62.  1.100
filebrowser  |   libavfilter    11.  4.100 / 11.  4.100
filebrowser  |   libswscale      9.  1.100 /  9.  1.100
filebrowser  |   libswresample   6.  1.100 /  6.  1.100
filebrowser  | Input #0, matroska,webm, from '/files/Yukui/Before I Rise.mkv':
filebrowser  |   Metadata:
filebrowser  |     title           : Before I Rise-茅森 月歌 歌詞付き
filebrowser  |     COMMENT         : https://www.youtube.com/watch?v=QZ6SrtAGuNE
filebrowser  |     ARTIST          : 「東方Motoki」
filebrowser  |     DATE            : 20221227
filebrowser  |     DESCRIPTION     : Heaven Burns Red テーマソング
filebrowser  |                     : 茅森 月歌 バージョン
filebrowser  |     SYNOPSIS        : Heaven Burns Red テーマソング
filebrowser  |                     : 茅森 月歌 バージョン
filebrowser  |     PURL            : https://www.youtube.com/watch?v=QZ6SrtAGuNE
filebrowser  |     ENCODER         : Lavf61.1.100
filebrowser  |   Duration: 00:05:26.61, start: 0.000000, bitrate: 468 kb/s
filebrowser  |   Stream #0:0(eng): Video: vp9, yuv420p(tv, bt709), 1920x1080, SAR 1:1 DAR 16:9, 60 fps, 60 tbr, 1k tbn (default)
filebrowser  |     Metadata:
filebrowser  |       DURATION        : 00:05:26.549000000
filebrowser  |   Stream #0:1: Audio: aac, 44100 Hz, stereo, fltp (default)
filebrowser  |     Metadata:
filebrowser  |       HANDLER_NAME    : ISO Media file produced by Google Inc.
filebrowser  |       VENDOR_ID       : [0][0][0][0]
filebrowser  |       DURATION        : 00:05:26.612000000
filebrowser  | Stream mapping:
filebrowser  |   Stream #0:0 -> #0:0 (vp9 (native) -> mjpeg (native))
filebrowser  | Press [q] to stop, [?] for help
filebrowser  | Output #0, image2, to 'tmp/thumbnails/videos/0997436eb12a62dd6829b1b87a3507d9.jpg':
filebrowser  |   Metadata:
filebrowser  |     title           : Before I Rise-茅森 月歌 歌詞付き
filebrowser  |     COMMENT         : https://www.youtube.com/watch?v=QZ6SrtAGuNE
filebrowser  |     ARTIST          : 「東方Motoki」
filebrowser  |     DATE            : 20221227
filebrowser  |     DESCRIPTION     : Heaven Burns Red テーマソング
filebrowser  |                     : 茅森 月歌 バージョン
filebrowser  |     SYNOPSIS        : Heaven Burns Red テーマソング
filebrowser  |                     : 茅森 月歌 バージョン
filebrowser  |     PURL            : https://www.youtube.com/watch?v=QZ6SrtAGuNE
filebrowser  |     encoder         : Lavf62.3.100
filebrowser  |   Stream #0:0(eng): Video: mjpeg, yuv420p(pc, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 60 fps, 60 tbn (default)
filebrowser  |     Metadata:
filebrowser  |       encoder         : Lavc62.11.100 mjpeg
filebrowser  |       DURATION        : 00:05:26.549000000
filebrowser  |     Side data:
filebrowser  |       cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: N/A
filebrowser  | [image2 @ 0x7f7f32866300] The specified filename 'tmp/thumbnails/videos/0997436eb12a62dd6829b1b87a3507d9.jpg' does not contain an image sequence pattern or a pattern is invalid.
filebrowser  | [image2 @ 0x7f7f32866300] Use a pattern such as %03d for an image sequence or use the -update option (with -frames:v 1 if needed) to write a single image.
filebrowser  | [out#0/image2 @ 0x7f7f327bd040] video:59KiB audio:0KiB subtitle:0KiB other streams:0KiB global headers:0KiB muxing overhead: unknown
filebrowser  | frame=    1 fps=0.0 q=10.0 Lsize=N/A time=00:00:00.01 bitrate=N/A speed=0.0382x elapsed=0:00:00.43    
filebrowser  | 2025/09/14 22:52:20 [INFO ] middleware.go:540: GET     | 200 | 172.18.0.130:43288 | Yukui        | 715ms        | "/api/preview?path=%2FBefore%20I%20Rise.mkv&key=1757908303300&source=Data&inline=true"

• If I use the "native" player of the browser I have this:

How to reproduce?
Open a .mkv video on Firefox or Firefox-based browser.

[gtsteffaniak]

I don't think this ever worked

[Kurami32]

I don't think this ever worked

I might be mixing some things as sometimes I play them on chromium... (sorry)

But could be possible add support for this?

Also, no rush with this, as nobody else were complaining. I think that other issues have more priority

[gtsteffaniak]

BTW the plyr doesn't add any video player support and there is no other method than waiting for the browser to support it for video.

Technically I could add some backend conversion, but that is an awful idea.

https://www.reddit.com/r/firefox/comments/1n6b91k/mozilla_firefox_is_officially_getting_mkv_video/

I'll leave this issue open because it would be nice to know what browsers work with this, I can't find a compatibility matrix online. So if you could do some testing that would be great.

[Kurami32]

BTW the plyr doesn't add any video player support and there is no other method than waiting for the browser to support it for video.

Yup, I know. Plyr just works on top of the html player, and is still relying on what the browser supports.

Technically I could add some backend conversion, but that is an awful idea.

I can imagine that... I wonder how many time could take for load the entire video, as ffmpeg takes its time converting.

So if you could do some testing that would be great.

I will try! If I can find something I'll comment here again.

Also, thanks for your reply!

[Kurami32]

So... I researched a bit and well, .mkv is a container of different codecs of video and audio. This chart about codecs support between browsers can help (Since you couldn't find one about .mkv specifically). Here is also a test video for see if mkv's videos can play on the browser.

I tried some things, I'll list them:
Firefox:

• On the current Firefox stable no one single .mkv video is working. Chromium-based browsers plays them fine, I don't know about safari.

• On Firefox Nightly, only some .mkvvideos play. TLDR: Just the ones which have h264 video format, I tried with vp9, av1, containerized on .mkv (no success).

• Regardless to audio format, if is opus don't will load, some other audio codecs is the same. I tried h264 video + opus audio, and no success too.

• On about:config of Firefox you can also enable h265 and hevc support, this can help with those types of videos.

Things that I tested on filebrowser:

• I separated a .mkv video which contains a h264 video and aac audio on separated files (video .webm and audio .aac) with ffmpeg, and they work.

• I did the same with a container with opus audio, and h264 video. The video play, the opus audio too, but on the wrong player.

So, summarizing: We need to wait until Firefox gives full support for mkv. Chromium is fine, and Safari I'm not sure, the chart above shows that have some partial codec support (?)

I also found some useful websites:
For download free samples and test different types of media:
(If someone open a issue about some type of media, can be more easy for download some and do a test)

• Video samples
• Audio samples
  And... A site for view (on charts/comparison tables) what things are compatible across web browsers: https://caniuse.com/ You just search for the file format on the big search bar.

Well, I hope that you can find this useful!

[gtsteffaniak]

thanks a ton for this info. I converted this to a discussion to keep it around for others to see.

The whole video codec situation for browsers is annoying, but the mkv container compatibility matrix actually looks hopeful! especially knowing firefox is getting support. And I would imagine chrome soon too

I think this will resolve itself over time, thats hopeful. But for now this is good to know.