Buffer Overruns when creating FFV1/MKV with Access MP4 and QCTools

[iamdamosuzuki]

Version 2026-03-03 is giving me buffer overruns when capturing FFV1/MKV files with concurrent creation of Access MP4s and QCTools reports. The errors usually start around the 3 to 5 minute mark, and it seems to depend on the complexity of the signal. Color bars did not cause any buffer overruns after 8 hours of recording, but something like a tv program caused errors after 5 minutes. Because of this I think that it may have to do with the access file creation, which I assume would be more processor intensive for more complex signals.

Turning off the QCTools generation seems to fix the issue. In my use case I need the Access MP4s created but don't need the QCTools reports. I haven't tested turning off the Access MP4s and leaving QCTools on. I'll give that a shot at some point.

[retokromer]

Version 2026-03-03 is giving me buffer overruns when capturing FFV1/MKV files with concurrent creation of Access MP4s and QCTools reports.

Same here.

[iamdamosuzuki]

for what it's worth, this issue doesn't happen on an M4 Mac Mini with 14 cores. So if your computer is fast enough it's not an issue ;)

[iamdamosuzuki]

I did a few tests on my M2 mini, here's what I got

• FFV1 Preservation file + Access MP4 + QCTools = Buffer Overrun
• FFV1 Preservation file + Access MP4 = Good Capture
• FFV1 Preservation file + QCTools = Buffer Overrun

[privatezero]

Thanks for reporting @iamdamosuzuki! I also have run into buffer overruns on my end recently, but I was using an mac that is ancient at this point, so I figured it was a me problem. On my end the fix was turning off simultaneous QCTools generation as well.

[retokromer]

I tested on Studio M2 Max (2023).