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Oddly Muxed MKV won't Play #64
Description
I have an oddly muxed mkv that will not play in the official Jellyfin Android TV app using libass-android v.0.4.0, but will play and render subtitles in vlc, mpv and Jellyfin Android TV when forced to transcode via ffmpeg. When I try to play the mkv, ExoPlayer just remains a black screen. Upon checking the Jellyfin server logs, it seems playback is started but then instantly stops, then starts, then instantly stops. This continues until I back out of ExoPlayer in the client.
I previously tested this same mkv under v0.4.0-alpha01. It would take ~10 seconds to load in ExoPlayer, then Exoplayer would behave as though it was playing with the time bar advancing, but the screen was black without audio, After if I scrubbed forward or backward in the video, video, audio, and ASS subtitles would begin playing fine.
If i remux the mkv, keeping all tracks and fonts, in MKVToolNix, it play just fine on Jellyfin Android TV app using android lib-ass v.0.4.0. Unfortunately due to the contents of the mkv, I cannot upload it to GitHub. However I have provided it directly to the libass-android developers. However below is the results of mkvinfo on the mkv. Font attachments are listed first, so maybe it is an example of #24 ?
+ EBML head
|+ EBML version: 1
|+ EBML read version: 1
|+ Maximum EBML ID length: 4
|+ Maximum EBML size length: 8
|+ Document type: matroska
|+ Document type version: 4
|+ Document type read version: 2
+ Segment: size 764021203
|+ Seek head (subentries will be skipped)
|+ EBML void: size 45
|+ Segment information
| + Timestamp scale: 1000000
| + Multiplexing application: Lavf61.7.100
| + Writing application: HandBrake 1.10.2 2025090600
| + Segment UID: 0x00 0xab 0x5e 0xcd 0xd0 0x95 0x63 0xfd 0x08 0x47 0x18 0xad 0x7a 0x80 0x9c 0xf3
| + Date: 2025-12-06 23:25:08 UTC
| + Duration: 00:23:51.600000000
|+ EBML void: size 23944
|+ Attachments
| + Attached
| + File name: Adobe Arabic.ttf
| + MIME type: application/x-truetype-font
| + File data: size 639064
| + File UID: 10194682767914786793
| + Attached
| + File name: Arial.ttf
| + MIME type: application/x-truetype-font
| + File data: size 1036584
| + File UID: 4983637153085138619
| + Attached
| + File name: Comic Sans MS.ttf
| + MIME type: application/x-truetype-font
| + File data: size 260780
| + File UID: 17160943384340969397
| + Attached
| + File name: NotoSansThai-Bold.ttf
| + MIME type: application/x-truetype-font
| + File data: size 47480
| + File UID: 12236574870431856677
| + Attached
| + File name: Courier New.ttf
| + MIME type: application/x-truetype-font
| + File data: size 709600
| + File UID: 13117264485837572108
| + Attached
| + File name: DejaVu LGC Sans Mono.ttf
| + MIME type: application/x-truetype-font
| + File data: size 335068
| + File UID: 5679076098779715146
| + Attached
| + File name: Tahoma.ttf
| + MIME type: application/x-truetype-font
| + File data: size 310752
| + File UID: 15774701854306210447
| + Attached
| + File name: Times New Roman.ttf
| + MIME type: application/x-truetype-font
| + File data: size 68372
| + File UID: 7330604309854406032
| + Attached
| + File name: trebuc.ttf
| + MIME type: application/x-truetype-font
| + File data: size 254396
| + File UID: 4535829930236771672
| + Attached
| + File name: trebucit.ttf
| + MIME type: application/x-truetype-font
| + File data: size 252224
| + File UID: 13168963940546708504
| + Attached
| + File name: Verdana.ttf
| + MIME type: application/x-truetype-font
| + File data: size 149752
| + File UID: 868186613095368489
|+ Tags
| + Tag
| + Targets
| + Simple
| + Name: ENCODER
| + String: Lavf61.7.100
| + Tag
| + Targets
| + Track UID: 5225109363916210190
| + Simple
| + Name: DURATION
| + String: 00:23:50.012000000
| + Tag
| + Targets
| + Track UID: 8620017840777853092
| + Simple
| + Name: DURATION
| + String: 00:23:50.061000000
| + Tag
| + Targets
| + Track UID: 11415095522679811444
| + Simple
| + Name: DURATION
| + String: 00:23:50.061000000
| + Tag
| + Targets
| + Track UID: 16751839982319122323
| + Simple
| + Name: DURATION
| + String: 00:23:50.010000000
| + Tag
| + Targets
| + Track UID: 8256426983831499691
| + Simple
| + Name: DURATION
| + String: 00:23:50.010000000
| + Tag
| + Targets
| + Track UID: 2839041102447251620
| + Simple
| + Name: DURATION
| + String: 00:23:50.010000000
| + Tag
| + Targets
| + Track UID: 11207325616364365580
| + Simple
| + Name: DURATION
| + String: 00:23:49.990000000
| + Tag
| + Targets
| + Track UID: 7246396533440039254
| + Simple
| + Name: DURATION
| + String: 00:23:49.950000000
| + Tag
| + Targets
| + Track UID: 5988844275834955331
| + Simple
| + Name: DURATION
| + String: 00:23:49.990000000
| + Tag
| + Targets
| + Track UID: 15922255043847189833
| + Simple
| + Name: DURATION
| + String: 00:23:50.030000000
| + Tag
| + Targets
| + Track UID: 15065749791456124078
| + Simple
| + Name: DURATION
| + String: 00:23:50.300000000
| + Tag
| + Targets
| + Track UID: 12529485237601311234
| + Simple
| + Name: DURATION
| + String: 00:23:51.600000000
| + Tag
| + Targets
| + Track UID: 7317159775326770146
| + Simple
| + Name: DURATION
| + String: 00:23:51.600000000
|+ Cluster
Activity
[-]Oddly Muxd MKV won't Play[/-][+]Oddly Muxed MKV won't Play[/+]peerless2012 commentedon Mar 10, 2026
@moi15moi Do you think so?
moi15moi commentedon Mar 10, 2026
No, that's not #24
moi15moi commentedon Apr 22, 2026
I'm not able to reproduce the problem with the demo app
ethaldeman commentedon Apr 22, 2026
I can test the mkv in wholphin's implementation of android-libass tomorrow. That may help confirm if it is an issues with Jellyfin Android TV app's implementation.
ethaldeman commentedon Apr 22, 2026
I tested using Wholphin's implementation of android-libass. It to failed to play the mkv. The seek bar seems to advance at a normal rate, but the video is always black despite where I scrub too. Wholphin's mpv can play it just fine.
Not sure how far you are going to investigate this or if this is an ExoPlayer or android-libass issue, but https://github.com/damontecres/Wholphin/releases/tag/develop-libass is a link to Wholphin with android-libass. It will formally be included the next v0.6.3 release.
ethaldeman commentedon May 29, 2026
https://www.dropbox.com/scl/fi/dq8pg95uvk5ayfhpbqifg/Last_Cluster_ASS.mkv?rlkey=hv6ysrcoltu7qlvbo8bnxrrzn&st=hfr22xoz&dl=0 is a link to a copyright free mkv with ASS subtitles which exhibit the issue described. The issue seems to be related to mkv that have their track information in the end cluster verses the first cluster. Furthermore the issue seems to be related to ExoPlayer and not libass-android specifically. Thus I am closing this ticket.
https://help.mkvtoolnix.download/t/i-need-to-produce-the-mkvinfo-outputs-not-enough-information-e-g-no-track-information-problem/1570 has some additional details.
ethaldeman commentedon May 31, 2026
Since I could reproduce the issue in the Exoplayer demo app, I opened a ticket at androidx/media#3250