Hi,
I'd like to know if it's ok to convert AAC files that are supposed to be loseless files to FLAC formats ? and if so how can I do in under mac osx or linux ?
I assume you are actually referring to Apple's lossLESS format, as it wouldn't make much sense to convert something in Apple's lossY Advanced Audio Coding (AAC) format to FLAC. The file wouldn't sound any better; it would only get bigger. You might as well keep it in AAC and let Slimserver convert it on the fly to PCM whenever you actually play it.
Files in Apple's lossless format have the same extension (.m4a) as files in AAC (Advanced Audio Coding), Apple's lossy format widely used on the iPod. As others have pointed out, Apple uses MPEG-4 containers for both formats, hence the common file extension, but inside they're quite different.
The big problem with Apple's lossless format is that it's proprietary, and open-source decoders like faad2 that handle .m4a files containing AAC can't handle it. I haven't seen any documentation that would allow someone to write an open source implementation that could be dropped into Slimserver, for example.
However, you can use iTunes to convert Apple's lossless compression format into something more friendly, like WAV, and then feed that to flac. To do this, bring up the Preferences panel in iTunes and select the "WAV Encoder" option for the "Import Using" field. Close the preferences window. This will put the entry "Convert Selection to WAV" on the iTunes "Advanced" menu. Assuming the files you want to convert are already in your iTunes library, select them and then the aforementioned "Convert Selection to WAV" command. This will add entries to your iTunes library for the selected items in WAV format. On my version of iTunes (4.7.1 on Mac OS X), at least, it leaves the originals intact.
Now you can extract the new WAV files from your iTunes library and do whatever you want with them.
There doesn't seem to be a "convert selection to FOO" command in iTunes, where FOO is any one of its supported formats. It only seems to have the one command that will convert a selection into whatever your currently selected format is for importing music from a CD.
It really is too bad that Apple -- who made a seminal breakthrough in adopting an open-source operating system (BSD) as its foundation for OS X -- chose to ignore a perfectly good open lossless compression technology (FLAC) in favor of its own proprietary scheme. I just can't see any advantages to it, other than built-in support in iTunes. Both lossless compression algorithms (Apple and FLAC) have about the same compression ratio, about 50% on average and somewhat better on quiet classical music.
--Phil _______________________________________________ Discuss mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/discuss
