FFmpeg audio export fails with -22 (Invalid Argument)

[generic-pers0n]

Describe the bug
When exporting audio, avcodec_encode_audio2 fails with a return value AVERROR(EINVAL) (or -22). This indicates an invalid argument being passed to avcoded_encode_audio2().

To Reproduce
Steps to reproduce the behavior (as tested by me):

1. Record or open (obtain) some audio
2. Go to Export > Export Audio...
3. Select 'Custom FFmpeg Export
4. For the format, select 'OGG'. For the codec, select either codec available for the OGG format (either libvorbis or flac).
5. Click 'Save'
6. Fill in the metadata fields with any value (or leave them blank)
7. See error

Expected behavior
The export should succeed, providing completely exported audio.

Additional information (please complete the following information):

• OS: Pop!_OS 21.10
• Version: Latest Saucedacity git

Additional context
This issue was discovered while reorganizing FFmpeg support in Saucedacity. It was originally thought that the reorganization caused the error, but further investigation found that this error persisted in builds without any reorganization work (i.e. before the reorganization work was done).

[generic-pers0n]

Good news! FFmpeg works again in Saucedacity, after switching Saucedacity over to Audacity's lib-ffmpeg-support. Rather than keeping that as a library, however, it has been integrated into Saucedacity's core (i.e., src/ffmpeg). This issue will be closed once lib-ffmpeg-support is merged into main.

[generic-pers0n]

Oh yeah, funny coincidence I just realized: this issue (#22) involves an error code of -22. Nice.