[BUG] Passthrough audio changes sample rate on multiple audio streams

[potejan]

Seems like ffmpeg's (default?) behavior is to copy the first audio track only. I can get it to copy both audio streams by using:

-map 0

The sample rate is preserved. I can also force the first stream to be skipped like this:

-map 0 -map -0:a:0

Sadly, in both cases the "correct" audio stream is silent, apart from a high-pitched buzz at the start...