I have about 300 gigs of ALAC files (m4a container) with well groomed metadata, album art, etc. (Original source: CD rips with dbPowerAmp). I want to convert my music library to 128kbps AAC (still m4a) to save on hard drive space on a small server.
The solution I'm hoping for is a command line based option using ffmpeg or the like. There's nothing Mac-specific about doing it that way but given it's all Apple codecs and I'm doing the conversion on a Mountain Lion box I thought I'd ask here. I can manage most of the shell scripting myself but I don't know ffmpeg well enough to be sure that it retains metadata and album art.
I've done a conversion in the past with iTunes 10; there's a trick where you manipulate "Convert higher bit rate songs to 128 kbps AAC". But the conversion quality is not sufficient. iTunes rewrites filenames in various circumstances, particularly when any non-ASCII is involved. Also it takes more than 20 hours to do the conversion and there's no clean way in iTunes to keep track of what's converted if the batch is interrupted.
