Convert OGG files with metadata to m4a for iPod

-c:a aac song.m4a For iTunes / iPods, we need the AAC coded, in the M4A container.

-map_metadata 0:s:a:0 Metadata for OGG tracks is stored at the stream level, so if you just try to copy metadata it won’t work, since the AAC encoder can only store global metadata. That’s what this bit does.

-aac_pns 0 AAC added a feature called “perceptual noise substitution” which iPods don’t support, so this needs to be disabled.

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