BUG: something amiss with genre fields in m4a/mp4

[MrSinatra]

5.63 / Win7

so i normally deal in mp3 and flac, and i don't have many m4a/mp4 files, so i didn't notice this until now.

however, at some point a few versions back i standardized all my files with winamp to a set list of genre tag possible values. np, winamp seemed to do it fine.

i have rescanned many times, and i have even done the right click, "read metadata on selected items" thing, and i think i've even done clear ML and scanned from scratched, or even copied the files to other machines, and still gotten the genre values that i set. when i do view file info i get the right value as well.

so whats the problem you say? everything seems to be as intended...

well, i was doing some routine maint on the collection, so i ran everything thru mp3tag 2.52, and suddenly i notice some strange values in the values for genres for these files. some are correct, meaning what i set, but some are values i don't use, and that DON'T appear in winamp AT ALL.

i do "extended tags" and indeed, i only see what mp3tag reports, not what winamp reports.

so the question is which is wrong? i thnk it has to be winamp, but i haven't proven it yet either way. but what i can't fathom, is how both apps are divergent, even after specifically told to "refresh" whats displayed?

and if it is winamp thats in error, how is it that these errors aren't corrected by such refreshing? or [possibly] persisting thru ML clears / new installs?

should i post some example files? or is this a known issue? can anyone confirm?

[MrSinatra]

just floating an idea here, but perhaps there is some multiple frame/field, null character entry kind of thing going on? and winamp reads one, mp3tag the other? how would i confirm? (i don't use them)

[ryerman]

Originally Posted by MrSinatra

just floating an idea here, but perhaps there is some multiple frame/field, null character entry kind of thing going on? and winamp reads one, mp3tag the other? how would i confirm? (i don't use them)

There is a command line application called Exiftool that can read the tags of many different file types, including m4a and mp4. The application is well documented and supported but there is a steep learning curve.
However, if you provide an example, I will use Exiftool to read the file(s) and post the results.
There may be some information exposed that you can use to clarify the issue.

[Aminifu]

Originally Posted by MrSinatra

just floating an idea here, but perhaps there is some multiple frame/field, null character entry kind of thing going on? and winamp reads one, mp3tag the other? how would i confirm? (i don't use them)

Interesting.

Don't know if you have found a bug or different design approaches for supporting these tags. I hope you take ryerman up on his offer.

Since WA is my player of choice, I use multiple 3rd party taggers, that match what WA displays for each file type, as applicable.

I also delete all tags and re-add them fresh when I do tag maintenance to try to avoid multiple entries and other weirdness that may happen when adding to or updating existing tags.

[MrSinatra]

here's one of them:

http://www.mediafire.com/?d75sddl9alxsca8

for me, its ONLY m4a/mp4 files that have this issue; i have about 6 with the issue. most have the genre value i set. i have 42 in all, out of 60k+ others, but these were all downloads. still, i have at least 5k of downloads of other file types, none of which do this.

i think multiple frames, with each app picking the other, is the most likely explanation at this point...

[ryerman]

Here is the Exiftool report.
"-b option" in entries of the form "(Binary data 124 bytes, use -b option to extract)" refers to an Exiftool option. For example, if the tag field was "Picture", the data could be extracted as an image file. Of course MrSinatra does not have album art in this file but I don't know how to extract the binary data that are here. Perhaps the discrepancies are in the binary data.

[MrSinatra]

ok, so thats interesting...

"Classic Rock" is the correct genre, and what shows in winamp.

so why would mp3tag show something else?

what do you see for genre in winamp and also in mp3tag?

[Aminifu]

Curious.

WA says genre is Punk Rock. MP3Tag 2.52 says Alternative & Punk. TagScanner 5.1 says Classic Rock.

I suppose it's possible that some apps read the text string that you entered and others use a pointer to a lookup table and the tables are arranged differently.

More curious.

When I use the edit box list in WA to change the genre to Classic Rock. It says that in WA and TagScanner, but MP3Tag still says Alternative & Punk.

[MrSinatra]

Originally Posted by Aminifu

Curious.

WA says genre is Punk Rock. MP3Tag 2.52 says Alternative & Punk. TagScanner 5.1 says Classic Rock.

I suppose it's possible that some apps read the text string that you entered and others use a pointer to a lookup table and the tables are arranged differently.

but then why would my winamp say Classic Rock and yours not?

Alternative & Punk is what my mp3tag says.

lets try this one:

http://www.mediafire.com/?wfagp9fsftei586

[Aminifu]

This is really strange.

The Girl I Knew Somewhere says Adult Pop in MP3Tag and TagScanner, but Classic Rock in WA.

When I use MP3Tag to change it to Classic Rock, all 3 now say Classic Rock.

[Aminifu]

Hi MrSinatra,

You have stumbled on to something. I've made a note to keep an eye out for further info on tagging these formats. Hopefully DrO and DJ Egg (and others) will drop in their 2 cents on this.

[MrSinatra]

ok, now thats a strange case for you, b/c that one is the same for me, its "Adult Pop" in both my winamp, and my mp3tag.

are you using some plugin, decoder, filter, etc, or something that isn't stock for mp4/m4a?

try this one:

http://www.mediafire.com/?21pjtswkbfflp56

[Aminifu]

That Monkees's tune says Classic Rock in WA, Adult Pop in TagScanner, and Pop-Rock Oldies in MP3Tag.

As far as I know WA is using it's stock decoders, all the WA options are setup for this. But these file types are not setup to be opened by WA. I could change that to see what would happen, but I don't think it would help explain anything.

I am using a codec pack (Shark007) for running videos with WMP, but they should not be overriding WA's decoders for audio files.

[MrSinatra]

my winamp says Adult Pop, and my mp3tag says exactly what your mp3tag says.

so in all 3 cases, our mp3tags agree with each other.

i still wonder if its a multiple frame issue, and mp3tag is just predictable in its handling of that, while winamp is not?

or if its something else completely?

i find the whole thing very, very weird.

[Aminifu]

It's another example of what happens in the PC environment when coders apply standards differently. I just look for as much consistency as possible across the apps I use.

If you change the genre tag with MP3Tag, does WA and MP3Tag then agreed? They do on my system.

[Aminifu]

My Shark007 codec pack was overriding WA's decoders. I had m4a files set to open with WMP. I redownloaded the files and changed to have WA open them. Now I get the same results you do with WA and MP3Tag.

So the decoders being used by each app do have something to do with this.

[Aminifu]

Some of your m4a downloads may have been made or tagged with iTunes. Due to the 'tricks' iTunes plays with file headers, trying to re-tag files tagged by iTunes with some other app could cause problems. A quick search turned up some old threads about this, mentioning m4a files in particular. Most of what I saw had to do with DRM protection, but some mentioned issues with non-DRM m4a files too.

[MrSinatra]

Originally Posted by Aminifu

If you change the genre tag with MP3Tag, does WA and MP3Tag then agreed? They do on my system.

i haven't tried yet as i want to keep the examples intact and besides, i was already fairly sure that would work.

Originally Posted by Aminifu

My Shark007 codec pack was overriding WA's decoders. I had m4a files set to open with WMP. I redownloaded the files and changed to have WA open them. Now I get the same results you do with WA and MP3Tag.

So the decoders being used by each app do have something to do with this.

yeah, i figured it was your winamp install b/c mine is fairly default/stock. so now the question is why the discrepancy between mp3tag and winamp?

Originally Posted by Aminifu

Some of your m4a downloads may have been made or tagged with iTunes. Due to the 'tricks' iTunes plays with file headers, trying to re-tag files tagged by iTunes with some other app could cause problems. A quick search turned up some old threads about this, mentioning m4a files in particular. Most of what I saw had to do with DRM protection, but some mentioned issues with non-DRM m4a files too.

yeah, itunes prob made them, you can see that in mp3tag's extended tags.

so, at this point i'm left thinking it must be a multiple frame issue. it would be nice if DJ Egg or DrO would explain the winamp/mp3tag discrepancy, and also why/how your 3rd party decoders would alter results.

[MrSinatra]

Originally Posted by MrSinatra

it would be nice if DJ Egg or DrO would explain the winamp/mp3tag discrepancy, and also why/how your 3rd party decoders would alter results.

pretty please?

[MrSinatra]

bump

[DJ Egg]

Hey

I couldn't reproduce the problem.

I don't have mp3tag, but with your sample files, the genre tag was the same (and correct) in all of Winamp, WMP, VLC & MPC.

Maybe there's some bug with mp3tag's reading of mp4 tags?

[MrSinatra]

Originally Posted by DJ Egg

Hey

I couldn't reproduce the problem.

I don't have mp3tag, but with your sample files, the genre tag was the same (and correct) in all of Winamp, WMP, VLC & MPC.

Maybe there's some bug with mp3tag's reading of mp4 tags?

yeah, i am starting to think the problem is on mp3tag's side. pretty uncommon, as usually it sets the standard for proper tagging.

my theory is there are multiple genre frames in these mp4s of mine, and for whatever reason, mp3tag chooses to display the one frame instead of the other. however, what confuses me is why both frames then don't show up in extended tags. i think i might report this as a bug over in their forums.

DJ Egg, can you please explain why when 3rd party decoders are used it changes what genre is displayed in winamp?

(also, mp3tag is free, i def think you should check it out)

EDIT:

http://forums.mp3tag.de/index.php?showtopic=16124