That tag is TLEN. It should be filled (at least!) for vbr mp3 files…. Not all tagger/encoders do that though.
Right, now I see. I found this was added to lame only recently (v3.98a11) fwiw.
I went ahead and downloaded the latest nightly and it does indeed produce correct times. (Thanks!) It looks like things have come quite a way since the stable release (the .deb pkg is more than four times the size and now requires libsqlite0).
Right (ish). About the xing tag, anyway. The gapless tag is another story.
I shall go and read up on this some more. I didn’t know there was metadata outside the id3 tags. Maybe I can find a tool that will read the xing tag and write a TLEN tag to my collection.