Author Topic: Familiar with ALAC files??? Need help...  (Read 6710 times)

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Offline jasonsobel

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Re: Familiar with ALAC files??? Need help...
« Reply #15 on: January 11, 2014, 10:05:37 PM »
and there's our answer:

the last post of this thread (which you linked to):
http://www.head-fi.org/t/656315/alac-md5-checksum-inconsistency

leads to the Binary Comparator component for foobar:
http://www.foobar2000.org/components/view/foo_bitcompare

download and install that component.

interestingly, when decoded the ALAC file to WAV, I got the same error:

Quote
1 out of 1 tracks converted with minor problems.

Source: "F:\_ARCHIVE\Malkmus\2009\malkmus2009-05-08\original ALAC files\09.m4a"
  Error flushing the decoder: Unsupported format or corrupted file

BUT, even with the error, I ended up with a WAV file.  Then, using the Binary Comparator component, I was able to verify that the audio streams in the ALAC and in the WAV were identical.

Quote
All tracks decoded fine, no differences found.

Comparing:
"E:\temp\09.m4a"
"E:\temp\09.wav"
No differences in decoded data found.


from this page:
http://wiki.hydrogenaudio.org/index.php?title=Foobar2000:Components_0.9/foo_bitcompare

Quote
This is useful to verify whether different files - typically lossless files - contain exactly the same audio data. The component compares only decoded audio data, presence of tags does not affect the results.

and that's exactly what you're trying to do.  Now, I don't know what exactly the issue is with the "minor problem" that foobar reports.  but my guess is that it's some weird header or something in the ALAC, and that it's something that doesn't actually affect the audio.
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Offline twatts

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Re: Familiar with ALAC files??? Need help...
« Reply #16 on: January 11, 2014, 10:08:40 PM »
and there's our answer:

the last post of this thread (which you linked to):
http://www.head-fi.org/t/656315/alac-md5-checksum-inconsistency

leads to the Binary Comparator component for foobar:
http://www.foobar2000.org/components/view/foo_bitcompare

download and install that component.

interestingly, when decoded the ALAC file to WAV, I got the same error:

Quote
1 out of 1 tracks converted with minor problems.

Source: "F:\_ARCHIVE\Malkmus\2009\malkmus2009-05-08\original ALAC files\09.m4a"
  Error flushing the decoder: Unsupported format or corrupted file

BUT, even with the error, I ended up with a WAV file.  Then, using the Binary Comparator component, I was able to verify that the audio streams in the ALAC and in the WAV were identical.

Quote
All tracks decoded fine, no differences found.

Comparing:
"E:\temp\09.m4a"
"E:\temp\09.wav"
No differences in decoded data found.


from this page:
http://wiki.hydrogenaudio.org/index.php?title=Foobar2000:Components_0.9/foo_bitcompare

Quote
This is useful to verify whether different files - typically lossless files - contain exactly the same audio data. The component compares only decoded audio data, presence of tags does not affect the results.

and that's exactly what you're trying to do.  Now, I don't know what exactly the issue is with the "minor problem" that foobar reports.  but my guess is that it's some weird header or something in the ALAC, and that it's something that doesn't actually affect the audio.

Too funny, I just saw that and I'm getting ready to run my own tests... 

Thanks!  Now I can get rid of these ALAC files!  Woohoo!

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Offline twatts

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Re: Familiar with ALAC files??? Need help...
« Reply #17 on: January 11, 2014, 11:28:14 PM »
A summary of Jason and my own Experiments with ALAC > WAV > FLAC via foobat, shntools, and TLH...

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 for all the help and the initial testing.  He also helped by reviewing my own experiments... 

Terry


« Last Edit: January 11, 2014, 11:40:27 PM by twatts »
Oh! That! No, no, no, you're not ready to step into The Court of the Crimson King. At this stage in your training an album like that could turn you into an evil scientist.

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Offline slslbs

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Re: Familiar with ALAC files??? Need help...
« Reply #18 on: January 12, 2014, 09:41:44 AM »
out of curiosity, what is a extra RIFF chunk?

I googled it, and the best i can tell it is just a way of labelling / tagging the file.
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« Last Edit: January 12, 2014, 09:43:31 AM by slslbs »
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Offline Marmar

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Re: Familiar with ALAC files??? Need help...
« Reply #19 on: January 12, 2014, 10:16:57 AM »
RIFF data is basically the bytes of metadata that helps programs determine what the container is/holds.....The RIFF format acts as a "wrapper" for various audio compression codecs.

AIFF is the Apple format.

In the simplest of descriptions, it tells windows/programs if it is a format, or strictly data.....what container......size.....padding....cue points.....etc.

Quote
"CHUNKS" are a fragment of information which is used in many multimedia formats, such as PNG, IFF, MP3 and AVI....etc

Each chunk contains a header which indicates some parameters (e.g. the type of chunk, comments, size etc.) In the middle there is a variable area containing data which are decoded by the program from the parameters in the header.

Since wav data has a lot of duplicate info in the chunks (hence why lossless encoding is possible) going from one codec to another may produce extra data that wasn't "needed" by one or the other codecs.....in that case you end up with extra CHUNKS of data (usually 0s) that gets stored in the file header info.
« Last Edit: January 12, 2014, 10:26:07 AM by Marmar »
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