View Full Version : Problem encoding to FLAC

2007-05-08, 04:11 AM
have a 24 bit 44100 wav file that I put in protools, performed minor eq, cut into tracks, PowR dither to 16 bit and bounced out as wav files (tracks).

When I try to encode to FLAC, it makes a FLAC file MUCH smaller than the wav file and give me errors stating- WARNING: skipping unknown sub-chunk 'ovwf'
and WARNING: skipping unknown sub-chunk 'umid'.

I can get a checksum or ffp file from these FLAC files.

When decoding the FLAC files back to wav, the files go back to the MUCH larger size of the original wav file as a wav file.

I have had the same results on macflac or traders little helper on a PC.

Is something wrong with the files? Am I doing something wrong? Can I upload these FLAC files?

2007-05-08, 04:57 AM
there is some extra information other than just the wav data being added by protools or some other audio editing program. Is there an option to save without this info


2007-05-08, 05:03 AM
Thanks Diggard. I will look but I don't think so.

I believe it was on the original recorder because the original file size is the same size as the file after bouncing out of protools.

I will check the recorder and reader also.

I thought the FLAC files and the wav files were not such as big of a difference in size before this. Maybe I'm mistaken. :hmm:

Thanks again. I think the files will be ok. :wave:

2007-05-08, 10:55 AM
Keyd, if I recall correctly, flac files are approximately 40-60% the size of the wav file. It depends on many things, so yours could be a bit more than that or a bit less than that, but they will definitely be smaller.

2007-05-08, 12:33 PM
I did include any other audio editing program as the possible culprit. I believe the UMID is Unique Material Identifier Data or some such thing, and was added to the audio data at some point possibly for European broadcast, the reason for the error is flac handles audio data only. Do you have a hex editing program that could open a copy of the wav and see what data is there?

from http://flac.sourceforge.net/faq.html#general__no_wave_metadata
FLAC is a general-purpose audio format, not just a compressed WAVE file format. There's a subtle difference. WAVE is a complicated standard; many kinds of data besides audio data can be put in it. FLAC's purpose is not to reproduce a WAVE file, including all the non-audio data that is in it, it is to losslessly compress the audio.

WAVE is a complicated standard; many kinds of data besides audio data can be put in it. Most likely what has happened is that the application that created the original WAVE file also added some extra information for it's own use, which FLAC does not store or recreate (see also). But the audio data in the two WAVE files will be identical. There are other tools to compare just the audio content of two WAVE files; ExactAudioCopy has such a feature.

2007-05-08, 01:22 PM
diggrd is right... CEP/Audition puts 'unknown sub chunks' in the header data on every file it saves. If its a cue sheet or something I need I'll save as APE, however to get the cue sheet back in CEP I have to first decompress the WAV before I load it in but that's another story.

Anyhow, don't worry whatsoever about 'unknown sub chunks' only worry about the audio content!

If you want to verify that the WAV and FLAC files are exactly identical audio content, generate an "st5" checksum from each and the hashes will be the same (see tutorial in my signature "checksums demystified").

The next thing you've got to check for and repair if necessary are SBEs or sector boundary errors. Run a "len check" on the resulting FLAC files .. this is important (see same tutorial)..

2007-05-14, 03:01 AM
Thanks alot.

All this information really helped!