It seems like the LAME INFO tag (described at http://gabriel.mp3-tech.org/mp3infotag.html) does include the number of padding samples. Bugs 1026 and 838 (they should probably be DUPed) cover this issue. I think it's a fixable problem for Squeezebox2...possibly not for initial launch, but shortly thereafter.
--Vidur
Familie Tromp wrote:
Hello Phil,
Information about amount of frames etc. is found on the following site. It says too that frames are added at the end AND the beginning of each mp3 file.
http://lame.sourceforge.net/tech-FAQ.txt
"3. Why does LAME add silence to the end of each song?
Extra padding at the end of a file can be caused by a couple of things:
1. Because the MDCT's are overlapped, it looks something like this:
<--576 MDCT coefficients--><--576 MDCT coefficients--><--576 MDCT coefficients-->
<-- 576 samples PCM output --><-- 576 samples PCM output -->
So no matter where you truncate your MP3 file, the last 288 samples of that granule will not be decoded. So LAME appends 288 samples of padding to the input file to guarantee all input samples will be decoded.
2. If the number of samples is not an exact multiple of 1152,
then last frame of data is padded with 0's so that it has 1152 samples.
Before lame3.56, we just added a few extra frames to make sure all internal buffers would be flushed. In lame3.56, we tried to pad with the exact minimum number of samples needed. And in lame3.80, we finally fixed the bitstream flushing so that the final mp3 frame is properly padded with ancillary data. "
Regards,
Karel Tromp
<reaction Phil Karn> Ah, I see. And I take it there's no field in the header that tells you how many audio samples are *really* in the track? If you had that, then you could just pad out the data during encode, and discard extra samples during decode.
What is the size quanta, i.e., how much padding can be needed, worst case?
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