Use lib-ffmpeg-support from upstream

[generic-pers0n]

It appears that upstream Audacity has updated and reworked their FFmpeg support. There also appears to be FFmpeg 5.0 support in the latest alpha of Audacity.

Given that, I am proposing that we update FFmpeg support. I particularly want to use Audacity's lib-ffmpeg-support minus the library form (it will be integrated in Saucedacity's core). Therefore, I will be making a new branch updated-ffmpeg-support, to update Saucedacity's FFmpeg support.

We will, of course, add our own changes, but for now, I plan to see how this works well with Saucedacity Maybe this could even resolve #22, but I am not exactly sure about that.

In relation to Saucedacity 1.2, there is a chance that this will likely make it for the final release. I would normally reconsider this during a beta, but since this could fix a bug, this will have to do and will probably be merged in to main before Saucedacity 1.2 is released.

[generic-pers0n]

It looks like FFmpeg works again. Testing with OGG (with FLAC) and FLV (with AAC) work, so I will commit this to updated-ffmpeg-support soon. I'm also looking forward to taking a look at lib-ffmpeg-support's interface too.

[generic-pers0n]

#31 contains lib-ffmpeg-support. This will be eventually merged and this issue will be closed once merged.