Garbage in audio when exporting tracks

[softrabbit]

Bug Summary

Exporting tracks leaves a few samples of garbage at the start of the audio files. Might be some buffer that should be cleared after each render but isn't?

Steps to reproduce

Export tracks as 16-bit WAV @ 44100 Hz.

Expected behavior

No garbage at start of audio files.

Actual behavior

Garbage at start of audio files, except for the first one rendered.

Screenshot

Ardour showing a couple of imported tracks:

Hachoir showing the data for one of the tracks, audio data highlighted in blue:

Affected LMMS versions

Master pulled and compiled on 2020-06-27, i.e. LMMS 1.2.1.702 (Linux x86_64, Qt 5.12.4, GCC 9.2.1 20191008)
Libsndfile 1.0.28 could be relevant, too.

[thmueller64]

I could not reproduce this behavior with the current master and libsndfile 1.0.28-7. Could you maybe share a project file?

[softrabbit]

issue-5548-shorter.mmpz.zip

A few more things I noticed:

• the garbage seems identical between files from the same export.
• looks like some degree of oversampling is needed for the bug to pop up, 1x seems to work fine.

Did a rebuild just in case something wasn't right, blowing away and recreating my build and target directories just to be sure before pulling and initing submodules and whatever the wiki says. Same bug still.

[thmueller64]

I can reproduce the behavior now with oversampling > 1. From what I can tell, the issue is that libsamplerate sometimes generates less samples than lmms expects. Could you please try out the draft PR above and check if the problem persists?

[softrabbit]

Cool! I'll check the PR tomorrow or possibly later today.

[softrabbit]

Looks like closing time, the fix is merged.