[moi15moi]

The previous code was assuming that, in the AttachedFile, the name and mime type were always before the data. This isn't true because the order is not guaranteed by the Matroska specification.

[peerless2012]

Does this fix #19 ?

[moi15moi]

No, the problem with #19 is that you call ass_render_frame before ass_add_font.

[peerless2012]

No, the problem with #19 is that you call ass_render_frame before ass_add_font.

Due my test, that issue is because of MatroskaExtractor will stop parse when reach Cue tag.

Is there any mkv to test this pr?

[moi15moi]

I don't know how I can edit the EBML of a mkv, so I don't know how I could create a mkv where the FileData is before FileName and FileMediaType.

I just know that the order isn't guaranteed, but I don't have any sample.

[moi15moi]

Due my test, that issue is because of MatroskaExtractor will stop parse when reach Cue tag.

For me, when I use opengl (with of course a mkv where the attachments section is at the end of the file), it sometimes show me the font and sometime it doesn't. So, that's why I think it call ass_render_frame before ass_add_font.

[peerless2012]

I don't know how I can edit the EBML of a mkv, so I don't know how I could create a mkv where the FileData is before FileName and FileMediaType.

I just know that the order isn't guaranteed, but I don't have any sample.

Is there any docs or other player process like this?

[moi15moi]

From https://www.matroska.org/technical/ordering.html

Except for the EBML Header and the CRC-32 Element, the EBML specification does not require any particular storage order for Elements.

[peerless2012]

We will kepp this pr and when we can find a mkv with this issue, then we can verify this pr and merge it.

[moi15moi]

As a reminder, AttachedFile looks like this (from https://www.matroska.org/technical/diagram.html)

+------------------------------------------------+
| Attachments | AttachedFile | FileDescription   |
|             |              |-------------------|
|             |              | FileName          |
|             |              |-------------------|
|             |              | FileMediaType     |
|             |              |-------------------|
|             |              | FileData          |
|             |              |-------------------|
|             |              | FileUID           |
+------------------------------------------------+

mkvmerge always writes FileName and FileMimeType before FileData, but as said previously, the order isn't guarantee.

With this script (mkv_reorder_attachment.zip), I created a mkv where FileData is before FileName and FileMediaType: output_mkv.zip.

With the command mkvinfo --ui-language en_US output.mkv, you can see that the FileData is indeed before the FileName and the FileMediaType:

|+ Attachments
| + Attached
|  + File data: size 36812
|  + File name: Jester.ttf
|  + MIME type: font/ttf
|  + File UID: 15477550427935747237

Without this PR, I was getting this exception:

2026-10-24 11:18:02.035 31312-31337 LoadTask                io.github.peerless2012.ass           E  Unexpected exception loading stream
                                                                                                      java.lang.IllegalArgumentException: Required value was null.
                                                                                                          at io.github.peerless2012.ass.media.extractor.AssMatroskaExtractor.binaryElement(AssMatroskaExtractor.kt:85)
                                                                                                          at androidx.media3.extractor.mkv.MatroskaExtractor$InnerEbmlProcessor.binaryElement(MatroskaExtractor.java:2069)
                                                                                                          at androidx.media3.extractor.mkv.DefaultEbmlReader.read(DefaultEbmlReader.java:145)
                                                                                                          at androidx.media3.extractor.mkv.MatroskaExtractor.read(MatroskaExtractor.java:596)
                                                                                                          at androidx.media3.exoplayer.source.BundledExtractorsAdapter.read(BundledExtractorsAdapter.java:147)
                                                                                                          at androidx.media3.exoplayer.source.ProgressiveMediaPeriod$ExtractingLoadable.load(ProgressiveMediaPeriod.java:1146)
                                                                                                          at androidx.media3.exoplayer.upstream.Loader$LoadTask.run(Loader.java:453)
                                                                                                          at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1100)
                                                                                                          at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                                                                                                          at java.lang.Thread.run(Thread.java:1572)
2026-10-24 11:18:02.039 31312-31336 ExoPlayerImplInternal   io.github.peerless2012.ass           E  Playback error
                                                                                                      androidx.media3.exoplayer.ExoPlaybackException: Source error
                                                                                                          at androidx.media3.exoplayer.ExoPlayerImplInternal.handleIoException(ExoPlayerImplInternal.java:927)
                                                                                                          at androidx.media3.exoplayer.ExoPlayerImplInternal.handleMessage(ExoPlayerImplInternal.java:903)
                                                                                                          at android.os.Handler.dispatchMessage(Handler.java:107)
                                                                                                          at android.os.Looper.loopOnce(Looper.java:242)
                                                                                                          at android.os.Looper.loop(Looper.java:362)
                                                                                                          at android.os.HandlerThread.run(HandlerThread.java:85)
                                                                                                      Caused by: androidx.media3.exoplayer.upstream.Loader$UnexpectedLoaderException: Unexpected IllegalArgumentException: Required value was null.
                                                                                                          at androidx.media3.exoplayer.upstream.Loader$LoadTask.run(Loader.java:474)
                                                                                                          at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1100)
                                                                                                          at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                                                                                                          at java.lang.Thread.run(Thread.java:1572)
                                                                                                      Caused by: java.lang.IllegalArgumentException: Required value was null.
                                                                                                          at io.github.peerless2012.ass.media.extractor.AssMatroskaExtractor.binaryElement(AssMatroskaExtractor.kt:85)
                                                                                                          at androidx.media3.extractor.mkv.MatroskaExtractor$InnerEbmlProcessor.binaryElement(MatroskaExtractor.java:2069)
                                                                                                          at androidx.media3.extractor.mkv.DefaultEbmlReader.read(DefaultEbmlReader.java:145)
                                                                                                          at androidx.media3.extractor.mkv.MatroskaExtractor.read(MatroskaExtractor.java:596)
                                                                                                          at androidx.media3.exoplayer.source.BundledExtractorsAdapter.read(BundledExtractorsAdapter.java:147)
                                                                                                          at androidx.media3.exoplayer.source.ProgressiveMediaPeriod$ExtractingLoadable.load(ProgressiveMediaPeriod.java:1146)
                                                                                                          at androidx.media3.exoplayer.upstream.Loader$LoadTask.run(Loader.java:453)
                                                                                                          at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1100) 
                                                                                                          at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) 
                                                                                                          at java.lang.Thread.run(Thread.java:1572) 

With this PR, the mkv now play normally and we can see indeed the font.