I have encountered a strange behaviour in Lame 3.95.1 when encoding files using "--preset cbr ***" (or the synonym "--cbr -b***"). When the bitrate is 32, 48 or 56 then no lame tag is written. This is true even if I add the -T command line option ("enable and force writing LAME tag").

The only reason I could presume for this is something to do with them being low bitrate files, but this makes no sense because bitrate 40 does write a lame tag.

3.93.1 writes lame tags for these bitrates. Looking at the betas and alphas, 3.94a15 writes them too, but 3.94b1 doesn't. I don't have any copies of alphas after 3.94a15, to determine exactly at what point the change happened.

OT: does the -T option actually do anything? Every other command line I have tried automatically writes a lame tag anyway, so it seems to be obsolete.

It is because there is not enough space to write a tag.

When the sampling rate is reduced, frames are actually bigger (because there are less frames per second). So when reducing bitrate to 40kbps, the combination of sampling rate and bitrate makes enough space for the tag.

Can you not use two frames for the tag?

I do not like this idea very much.

Neither do I. None of existing LAME tag readers would read that without modifications.

How did you make room for the tag in the 3.94 alphas and earlier versions?

Probably writing bigger frames that confused some players about bitrate/duration of the file.

The sampling rate was just different.

lame3.93 --preset cbr 56: 22kHz
lame3.95 --preset cbr 56: 24kHz