Align To Reference Track - sometimes fails, and makes my project crash

Help/How To
1

My earlier post under the “bug” category didn’t trigger any replies - maybe I was asking too much to recreate the test files required to reproduce.
So I give it another try after spending some more time preparing a complete test case, and some refinement in the steps to reproduce:
SC crashes.zip (5.3 MB)

  1. place the 3 files “TEST 2 crashes.mlt”, “TEST 2 Video 2 (Zero8) - audio track_crop.flac” and “TEST 2 Video 2 (Zero8)_crop_480p.mp4” into same folder. The FLAC file was generated from the mp4 file, so it is identical to the audio track of the video.
  2. Open the project file “TEST 2 crashes.mlt” in SC (tested with v250125 an v240913 on Win10): video and audio tracks are not aligned. Audio track starts later than video.
  3. Select video clip and “align to reference track” from context menu.
  4. Select track “audio only (R)” as reference track. So we expect that the video track gets shifted right to align with the beginning of the audio track.
  5. Click on “process and apply” in dialog. Watch the progess bars and: Nothing happens. The video track is still at the same position.
    ==> Oops 1: Why does the alignment fail, without any error message?

Anyway, lets try the other option: shift audio track left to align with the video track:
6. Select audio clip and “align to reference track” from context menu.
7. Select track “video + audio (L)” as reference track.
8. Click on “process and apply” in dialog. Watch the progess bars and hooray: The audio track gets shifted left so that both tracks are aligned.
9. Oh wait - let me change some filter settings, which I specified in my template in the audio track header: Click on the track header of the “audio only” track
==> Oops 2: Shotcut crashes

In short:

  1. Why can I not freely select the reference track (if there is enough room to shift a track left, without going into negative time), and why is there no error message if alignment fails?
  2. What is wrong with my template so that it makes SC crash?

The attachment also contains an application log (cropped and annotated), until the moment SC crashes.
Unfortunately I couldn’t find anything looking like a crash log under C:\Users<myname>\AppData\Local\Meltytech\Shotcut. Should there be any?

I’d really apreciate any insights or help to get this straight.

2

It fails because you added filters on the “Audio Only (R)” track that made it sound significantly different than the video clip. I disabled the filters on the audio track and the alignment worked.

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It isn’t an “error” when the algorithm is unable to find alignment. It either finds it or it doesn’t. If you are looking for feedback on the alignment process, click “Process”, not “Process + Apply”. When you do that, you can see the results of the processing step in the dialog:

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I recreated this and I have bookmarked this post for future debugging.

3

thanks @brian for your prompt analysis.
Yes the filters in the audio track attenuate the volume by 20dB and pan it all the way to the right. The audio in the video is panned all the way to the left, so that I can hear both audios in my speakers for checking if alignment is correct. Usually the the audio-only track is much louder, hence the lower volume.
I wasn’t aware that the filters are relevant for the alignment - thanks a lot for the clarification.
BTW on my PC (v250125) after “processing” I only get the red x-marker in front of the file name, but not the explanation “alignment not found”. This is a bit confusing.
It seems that the combination of the filters in the audio track prevents alignment. Unless I disable both, I don’t get alignment, reagrdless of the filters in the video track.

Looking forward to the result of your analysis regarding the crash.

4

Hover your mouse over the red x to see the popup message.