Saturday, 7. November 2009
I recently had several tracks stop playing in iTunes and they all had one thing in common, a duration of 789:57:13. The recommended solution for this problem is to re-rip or re-download the track. That wasn’t an option for some of these tracks because I purchased them through iTunes and the official Apple stance is that you are only allowed to download a purchased track once and I didn’t want to re-purchase the tracks. Restoring from backup also wasn’t an option for some of the tracks because they were munged in even my oldest backups.
The solution I found was faad and faac – Freeware Advanced Audio Decoder/Coder. It will decode unencrypted AAC/MP4 files and will happily ignore and correct the munged frame duration in the MP4 wrapper. I recovered a damaged track like this:
faad "09 This Devil's Workday.m4a" -o "09 This Devil's Workday.wav"
mv "09 This Devil's Workday.m4a" "09 This Devil's Workday.m4a.bad"
faac -w --artist "Modest Mouse" --title "This Devil's Workday" --album "Good News for People Who Love Bad News" --track 9 --disc 1 --year 2004 "09 This Devil's Workday.wav"
As faad was decoding the original track it showed that the MP4 wrapper’s duration was, but it corrected as it decoded it.
MP4 seems to have incorrect frame duration, using values from AAC data.
Decoding 09 This Devil's Workday.m4a took: 1.62 sec. 85.94x real-time.
When faad/faac were done I was able to re-import the track into iTunes and play it successfully.
I lost some of the iTunes metadata from the original track, mainly the cover art. iTunes automatically added the cover art when I re-imported it, but that only works for music in the iTunes library. In those cases, faac has an option to import cover art from an external image file. You can do the same thing with iTunes as well.
If you have a lot of tracks to repair, adding the metadata manually on the command line is tedious. However, it could be automated with a simple script that captures and processes the output of faad since it displays all the track metadata as it is processing.
Cross-posted on deanfranklin.net.