Changing volume control while a video is playing crashes app about qmplay2 HOT 19 CLOSED

I noticed a difference between the releases. I ran a video with subtitles enabled.

1. QMPlay2 22.08.21 - plays video without audio/subtitle/OSD issues.
2. QMPlay2 23.10.22 - crashes when video is about to display subtitles and no audio.

When I disabled subtitles:
Result: QMPlay2 23.10.22 - plays video without audio issues. Still crashes if video control is clicked.

When I disabled audio before playing video:
Result: QMPlay2 23.10.22 - plays video.

Enabled audio during playback:
Result: QMPlay2 23.10.22 - continues playing video. and enables audio - no issue.

Disabled audio during playback (while video/audio enabled), subtitles disabled):
Result: QMPlay2 23.10.22 - application exits.

Disabled audio before playback (video-enabled, audio-disabled, subtitles-enabled):
Result: QMPlay2 23.10.22 - plays video - application will exit before audio/subtitles is initially used in video playback.

I ran strace and Debugger. Will review possible resource lock or handshake condition between Haiku's BSoundPlayer control and QMPlay2 23.10.22.

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Note: This issue has something to do with QMPlay2 libass interaction on Haiku R1B4. I traced it back to the QMPlay2 22.10.23.
I've attached my Haiku build file showing previous QMPlay2 code build of libass 0.17.1 with QMPlay 22.10.23 before QMPlay2 23.02.05.

qmplay2-22.10.23_libass-0.17.1_haiku.txt

Workaround: Disabling libass support in QMPlay2 23.10.22 resolved our issues for now.

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Reviewing: 0c9cd8d

• "Improve ASS subtitles sync"

I think the new code commit tickles a resource deadlock mutex handling condition on Haiku R1B4. I'll research it more when time permits as I think this a Haiku R1B4 issue - not QMPlay2 22.10.23 at the moment.

Debug file:
QMPlay2-10879-debug-15-11-2023-08-37-10.txt

Backtrace message: "Can't access memory at address 0x7ff834ea8000"

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Here are the screenshots from QMPlay2 22.08.21 w/subtoitles enabled. I can also disable subtitles with this test video. (Note: I get the QMutex lockup eventually when moving through the frames (so, not a new issue with QMPlay 23.10.22 (i.e. it seems Haiku-specific when using both QMPlay2 versions)).

Here is the snapshot of the video playing on Youtube w/subtitles (CC) enabled. There is also a video transcript exact to the subttiles.:

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@zaps166 - We can close for now. The feature is not of high use yet on Haiku. Otherwise, QMPlay2 seems stable on Haiku. Thanks.

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Strange, nothing changed about volume. Can you use debugger and show where it crashes?
It shows OSD in video, cold you try to zoom in/out video to see if it display OSD properly?

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Aaah now I noticed it's 22 not 23. Please show me backtrace.

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Hmm, I didn't touch Haiku code except whitespace and NULL->nullptr changes. Also I don't have Haiku to test it.

You can catch the exception in debugger and see where the deadlock happen.

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Do you use Vulkan or OpenGL for testing?

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We use mainly use OpenGL. I enabled QMPlay's OpenGL option which ran a little slower in video playback due to OpenGL software rendering. No other issues. Runs A/V optimal with no other issues otherwise.

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Software Vulkan (mesa's lavapipe) should perform better than Software OpenGL in QMPlay2. Also subtitles works differently with Vulkan - maybe worth to try?

Is libass working stable with other software?

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OK. I switched to Vulkan which seems smoother. No major issues. libass seems to work with QMPlay 22.08.21 and other software without issues as far as I know. I think QMPlay2 22.10.23 was the starting point for the Haiku platform related OSD/subtitle issues. Possibly, Haiku-specific for now.

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Good that Vulkan is working better.

But strange issue with libass. I'm aware it'a s lot of work, but yould you find which commit caused this issue with libass?

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You can put qDebug() << "Point1"; before locking and qDebug() << "Point2"; after locking a mutex (put Point3 and 4 on another locking) and you'll see exactly where deadlock happens.

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1. I noticed the other players didn't show the subtitles of this test file.
2. Using Haiku's Debugger/gdb, QMPlay2 shows the initial subtitle line, then there is a A/V sync break in which the audio track still plays fine but the video frame iis locked showing the video display and initial subtitle line. (i.e. this is the point of error). Application seems fine (i.e. video bitrate/buffer status info is progressing) until you try to use GUI menu commands.
3. I added what I captured with Haiku's Debugger and gdb so far.

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Could you send the test file? Or it happen on any video files?

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Test file: https://youtu.be/oaqHdULqet0?si=pD6Uo3rdie1b0K-y
A/V error point: 0:33 / 2:19:04

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Hmm, this video doesn't have subtitles, only auto-generated which doesn't work in QMPlay2. How do you see subtitles there?

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I don't have any idea so far...

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