pfarrell Wrote: > Every Unix I know, Linux, etc. has a copy of diff, > and it has a --binary switch. Pat, I guess maybe you have a different version of diff than I do, but I've checked 3 different versions and none of them have a --binary switch. Specifically, I checked diff on OS X (GNU diffutils version 2.7), diff on Linux (GNU diffutils 2.8.1), and diff on Solaris (version unknown). I read the man pages for all for each one, and none of them included --binary.
On OS X and Linux, when comparing two different binary files diff simply said "Binary files <X> and <Y> differ." It gave the same result regardless of --binary, meaning it was ignoring the (presumably unrecognized) switch. On Solaris, diff complained --binary was an illegal option. The only way I could see any differences was to use the --text switch, though that output was pretty much unreadable. So, the good news and the weird news. First the good news: it does appear that ALAC is truly lossless and converts back to the same raw data as the original music, at least when using iTunes to do the conversion. Using the mov123 utility (built-in to SlimServer) doesn't generate the same files as using iTunes to do the conversion. I'm not quite sure what the reason is... using mov123 generates files that are about 50KB smaller than iTunes-generated AIFF files. It may be that AIFF includes support for metadata, and the iTunes-generated files include that metadata while the mov123-generated files do not. (Note that the 'file' utility recognizes AIFF, WAV, FLAC, and other audio formats, but it says the mov123 output file is just "data" ... apparently no recognized audio format.) Specifically, I used iTunes to create an ALAC file from the raw CD track, then used iTunes to convert that ALAC file to AIFF. I then used iTunes to convert the raw CD track directly to AIFF. The resulting filesizes were identical, but the files DID differ somewhat, however the differences were minor - only a few bits out of the entire 48MB files were different. As a check, I used iTunes to convert the raw CD track directly to AIFF a *second* time, and compared this to the first raw-to-AIFF file. They had the same filesize but ALSO differed in a similar manner to how the ALAC-to-AIFF file differed. Thus, I suspect that iTunes is incorporating time-specific values in the AIFF metadata, which would explain why two raw-to-AIFF files generated at different times differ by a few bits, yet have the same filesizes. The fact that the ALAC-to-AIFF file differed in the same way makes me reasonably confident that the original raw data is being properly recreated from ALAC. Unfortunately, there was no way for me to make sure that the output from mov123 really was the same as the original raw data. Through its optical-drive drivers and various voodoo disk caching mechanisms, OS X mounts the CD with the tracks already represented as AIFF files with metadata, i.e. the track files are already properly named (not just "track 1") and include other non-audio information. So without some independent utility to turn the CD track files (mounted and accessed as AIFF files even directly from the CD) into the same raw output as mov123 provides, I can't verify that mov123 actually turns ALAC into the same raw data as on the CD. BUT... the results using iTunes do make me reasonably confident that ALAC is converted properly back into the true raw data. Now the weird news... since OS X virtually pre-processes the CD tracks and represents them as AIFF files, they are accessed as big-endian. When I use 'flac' to convert these to FLAC with --endian=big, the resulting FLAC file has almost the same size as the raw data, i.e. there is ZERO compression! But if I use --endian=little, with no other changes in the encoding options, the resulting filesize is 40% smaller. Wha?! Anyway, though I'd update on that issue... it DOES seem ALAC is properly lossless and the original raw audio can be reproduced, at least when using iTunes... though what I *can't* verify is that mov123 properly reproduces the original raw audio, because of the apparent difference between AIFF and whatever mov123 is outputting. -- cepheid ------------------------------------------------------------------------ cepheid's Profile: http://forums.slimdevices.com/member.php?userid=3845 View this thread: http://forums.slimdevices.com/showthread.php?t=22635 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
