https://bugs.kde.org/show_bug.cgi?id=505578

Yash Bavadiya <[email protected]> changed:

           What    |Removed                     |Added
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                 CC|                            |[email protected]

--- Comment #16 from Yash Bavadiya <[email protected]> ---
I had a look at the two backtraces with debug symbols (attachments 183612 and
183613), and both crash in the same place, inside MLT's avformat producer
rather than in Kdenlive code.

Attachment 183613, thread 20303:

```
#0  avformat_find_stream_info () at /app/lib/libavformat.so.61
#1  get_basic_info (...) at producer_avformat.c:911
#2  producer_open (..., take_lock=0, test_open=0) at producer_avformat.c:1178
#3  producer_set_up_video (...) at producer_avformat.c:2988
```

Attachment 183612, thread 1 (the main thread):

```
#0  producer_open (..., take_lock=0, test_open=0) at producer_avformat.c:1241
```

Two things stand out. Both crashes are in `producer_open` reached from the lazy
reopen path, the "Reopen the file if necessary" branch that runs when the
format context is null, and in both cases `take_lock=0`, so the producer is
being opened without taking its own internal lock. The video reopen path passes
`take_lock=0` and locks `video_mutex` by hand around the call, while the audio
reopen path passes `take_lock=1`, so the locking is asymmetric between the two.

The other thing is that one crash is on a worker thread and the other is on the
main thread, and both dumps have 18 threads inside producer_avformat.c at the
moment of the crash. That fits the "random, happens when I am not expecting it"
description better than a specific user action does, since what varies is the
timing rather than the operation. The reported triggers, dragging a clip,
moving the playhead, zooming, importing, are all things that cause producers to
be opened or reopened.

Worth noting the file in 183613 is a .webm and in 183612 a proxy .mov, so it
does not look format specific.

I have not reproduced this locally and I am not claiming a specific root cause,
the line numbers in the trace are from the AppImage's MLT build so they do not
map exactly onto current MLT sources. But the crash is consistently in that
reopen path, so that seems like the place to look, and it may be worth raising
upstream with MLT rather than treating it as a Kdenlive bug.

@antimidia if you hit it again, a backtrace from a debug build would help
narrow it further, the two attachments above are the only ones in the ticket
with symbols and they are from 2025.

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