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LENGTH (running time field), TLEN in ID3 ?? in FLAC, [TOS #6: moved from General Audio]
HansBKK
post Aug 29 2012, 08:49
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I have a bunch of MP3s, some have a TLEN file, some don't, haven't come across any problems so far.

Some intertubes references say this can be important for "proper seeking with VBRs" whatever that means.

Other places say don't worry about it.

The newer part of my collection is mostly FLAC, and that seems to have no issue, but if the value is important when converting to MP3, will FB2K handle this automagically or should I embed a "LENGTH" field say via MP3Tag?

And I realize this may be a heretical question here, but is there a free toolset (in either/both senses) better than FB2K on windoze for converting from FLAC to MP3, I'm trying to get all the tags over and am finding I have to change quite a few of MP3Tag's default mappings in order to get the ID3 tags converted properly (e.g. CONTENT GROUP rather than CONTENTGROUP). And of course the coverart would be nice.
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HansBKK
post Sep 1 2012, 03:34
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QUOTE (HansBKK @ Aug 29 2012, 08:49) *
I have a bunch of MP3s, some have a TLEN file, some don't, haven't come across any problems so far.

Some intertubes references say this can be important for "proper seeking with VBRs" whatever that means.

Other places say don't worry about it.

The newer part of my collection is mostly FLAC, and that seems to have no issue, but if the value is important when converting to MP3, will FB2K handle this automagically or should I embed a "LENGTH" field say via MP3Tag?

And I realize this may be a heretical question here, but is there a free toolset (in either/both senses) better than FB2K on windoze for converting from FLAC to MP3, I'm trying to get all the tags over and am finding I have to change quite a few of MP3Tag's default mappings in order to get the ID3 tags converted properly (e.g. CONTENT GROUP rather than CONTENTGROUP). And of course the coverart would be nice.


I'm not sure why this got moved to an MP3-specific forum, since my question is mostly about my source FLAC files.

And no one knows whether the TLEN field is important or not?
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skamp
post Sep 1 2012, 07:56
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The TLEN field is imprecise and completely unreliable. Some progams put garbage in it. Neither FLAC or MP3 need it, AFAIK.


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db1989
post Sep 1 2012, 10:22
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QUOTE (HansBKK @ Sep 1 2012, 03:34) *
I'm not sure why this got moved to an MP3-specific forum, since my question is mostly about my source FLAC files.
The TLEN field is specific to MP3. FLAC neither natively has nor will ever need such a field. Moreover, using ID3 tags in FLAC is discouraged as non-compliant with the format’s standard.
Edit: I suppose that’s moot as I’ve now noticed that it was moved from General Audio rather than from the dedicated sub-forum for FLAC; even were this relevant to FLAC, the former obviously is not the right location when the latter is available.

You do not need to tell a competent MP3 encoder such as LAME how long its source file is; it can figure that out perfectly well by itself, and it will in addition create a destination file whose length is clearly specified without needing TLEN.

QUOTE
And no one knows whether the TLEN field is important or not?
Pretty much no, and it makes especially little sense in formats other than the one wherein it originated.

This post has been edited by db1989: Sep 1 2012, 10:52
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HansBKK
post Sep 3 2012, 07:53
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Thanks to you both for the clear and unambiguous answer.

I don't know much about this stuff (obviously) so please correct my below interpretation if I'm wrong.

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The TLEN field only pertained to MP3, and (its equivalent LENGTH) has never been relevant wrt to FLAC files.

Perhaps the field's spec was created back when VBR encoding was the new hotness, some players couldn't display the "time remaining" accurately without it.

However, all modern mainstream players retrieve the precise length value from the MP3-specific internal "?header" (in any case someplace not having anything to do with user-maintained tags) and therefore having a TLEN field is redundant, not just unnecessary but possibly misleading.

Therefore the consensus recommendation is to delete this field and its value wherever it may be found, at least in FLAC and MP3 files.
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db1989
post Sep 3 2012, 10:46
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I think you’re pretty much right-on with the background. But, via a blast from the past…
http://www.hydrogenaudio.org/forums/index....showtopic=83500
…I don’t know whether always deleting it is a good idea, either. tongue.gif I think the situation is that you needn’t worry about adding it manually, whether to MP3 (whose encoder will do that if it judges it to be advisable) or to FLAC (which has its own format), – but going through your MP3s and removing it might conceivably cause issues with reliant players (like the one you imagined), whereas it’ll almost certainly do no harm if left in place, being ignored in the worst-case scenario.

I’m glad you thought my answer was helpful, but please allow me to defer to anyone with better knowledge of MP3/TLEN than myself, just in case I’ve omitted or mistaken something! smile.gif

This post has been edited by db1989: Sep 3 2012, 10:47
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