ALAC support

[Igetin]

While running the following command:

ffmpeg -i input.avi -c:v libx264 -preset veryslow -crf 18 -profile:v main -level:v 4.2 -c:a alac -pix_fmt yuv420p -movflags +faststart output.mp4

I get the following error in console:

[fferr] [mp4 @ 0x1a76bc0] Could not find tag for codec alac in stream #1, codec not currently supported in container
[fferr] Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
[fferr] Error initializing output stream 0:0 -- 
[fferr] Conversion failed!

However, when running the same command with the actual FFmpeg CLI program on my computer, the command succeeds and the output is playable. So it's not actually a problem with the container, but probably the specific build of FFmpeg the web app uses?