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ALAC md5 checksum inconsistency

post #1 of 4
Thread Starter 

I am going to convert my flac files to alac for use with my iPhone and plan on deleting the original flac copies to save hard drive space. I want to make sure I can go back to flac with no quality loss should I decide flac better suits my needs in the future.
 

I know that they are both lossless and I should be able to go between flac and alac all I want with no degredation, but I think I might be doing something wrong.

Here is what I did:

FLAC to WAV in foobar2000

I took that WAV file into iTunes and converted it to ALAC

I then took that ALAC into foobar2000 and converted it back into WAV so I could compare the md5 checksum and make sure nothing was altered.
The checksums did not match

To test things I then ripped a fresh WAV from a CD

Using foobar 2000 I converted the original WAV to FLAC and back to WAV (this WAV matched the original WAV checksum)

Using iTunes I converted the original WAV to ALAC and then used foobar2000 to convert it back to a WAV (this WAV did not match the original WAV checksum)

What is it about ALAC that is preventing me from getting my original WAV file back? Am I doing something wrong? I am not messing with any tags whatsoever in iTunes. Is iTunes sticking tags into the file during the ALAC conversion anyway?


Thanks!


Edited by Splorfus - 3/20/13 at 2:11am
post #2 of 4
The difference is likely just headers in the WAV files. The actual PCM content is identical. To show this, use foobar's Binary Comparator component. Select two files, right click, utilities -> Bit-compare tracks.

Also, you can transcode FLAC to ALAC directly, without first decoding to WAV. See:
http://www.hydrogenaudio.org/forums/index.php?showtopic=92296
post #3 of 4

1. Foobar can do a "perfect" decode of ALAC to WAV.

2. The resulting WAV file is OK per Bit Compare for Foobar.

3. Comparison b/w the M4A and resulting WAV show "No differences in decoded data found".

4. However, the resulting WAV has "extra RIFF chunks" per SHNTOOLs.

5. This will result in WAV MD5s that may be erroneous.

6. Using the "Strip" function with SHNTOOLs will correct this problem.

7. Converting the non-stripped WAV to FLAC with Traders Little Helper will also correct this problem (unless you "keep foreign metadata").

8. The "stripped" WAV files and the WAV > FLAC > WAV files via TLH will give you the same WAV MD5.

 

Thanks to Jason Sobel for the help in figuring this out!

 

Terry Watts

post #4 of 4
Thread Starter 
Quote:
Originally Posted by twatts1000 View Post
 

1. Foobar can do a "perfect" decode of ALAC to WAV.

2. The resulting WAV file is OK per Bit Compare for Foobar.

3. Comparison b/w the M4A and resulting WAV show "No differences in decoded data found".

4. However, the resulting WAV has "extra RIFF chunks" per SHNTOOLs.

5. This will result in WAV MD5s that may be erroneous.

6. Using the "Strip" function with SHNTOOLs will correct this problem.

7. Converting the non-stripped WAV to FLAC with Traders Little Helper will also correct this problem (unless you "keep foreign metadata").

8. The "stripped" WAV files and the WAV > FLAC > WAV files via TLH will give you the same WAV MD5.

 

Thanks to Jason Sobel for the help in figuring this out!

 

Terry Watts

 

This worked perfect! Thanks!

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