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VSE - Improper audio on frame 1 when exporting to lossy-compressed audio
Open, Needs Triage by DeveloperPublic


Blender Version
Broken: 2.80

Short description of error
When audio from the vse is exported to lossy-compressed formats (mp3, ac3, aac), blender is adding an odd fadein on it. (see channel 6 in the attached blender screenshot).
It actually appears somewhat like a fadein in blender, but when imported into audacity, there is a .005 second silence, then instantly full volume.

Whats worse, this false fadein seems to override any keyframes on the first frame: if the audio has a 6 frame fade in keyframed in, it will do that weirdness for the first frame, then return to the proper volume for frame 2 and continue the fade in. This creates a kind of 'hump' where there should be a smooth transition. (See channel 3 in the attached blender screenshot)

Oddly, this bug does not happen on non-lossy formats (wav, pcm, flac) (see channels 4 and 7 on the attached blender screenshot).

Note: all these tests were done with a basic sinewave test tone for maximum visibility of the waveform.

Exact steps for others to reproduce the error
Load an audio file with audio immediately at the beginning into the vse
Add a fadein
Render audio out to a lossy compressed format (either in a video, or as audio alone)



Event Timeline

Can I add that the preview playback in the viewport doesn't exhibit this problem. It only manifests in the encoded output file. I'm not sure how far back this goes but I can confirm this has been a problem in 2.8 for several weeks now.

ok, this is weird... today im not getting the same issue with the 'bump' when exporting only audio, even compressed.... but I still see the issue every time when exporting to video/audio combined... but I now see it with ANY audio codec in video, not just lossy formats.

I do experience similar issues during preview, but not in rendered files, at least not "audibly"
This is quite contrary, to what's reported.

I never looked at cause of this issue, but I am pretty sure it's outside of scope of VSE code.