On Oct 3, 2006, at 8:30 PM, Matt Robbins wrote:
I am using libmad to handle mp3 access for my project ( www.xbat.org ). Our particular application requires fast, accurate seeking, and I have been successful in using header information to seek to the correct frame. I am having trouble, though when I set the decoder (from the "high-level" API) running. For many files it works fine, but for some, I get "bad main-data- begin pointer" errors for the first one or two frames decoded. Right now, I am circumventing the problem through the use of the MAD_FLOW_IGNORE symbol in the error callback function, but this results in the somewhat-undesirable behavior of decoding zeros for the first several frames. Is there a way around this, short of deliberately seeking several frames early and then discarding the unneeded data? Might this have something to do with bit reservoir encoding? Any help would be much appreciated.
You're right; it has to do with the bit reservoir. In general, to perform accurate seeking you must decode a few frames before the target frame in order to reload the reservoir.
You may want to review these messages on the subject of seeking:
http://www.mars.org/mailman/public/mad-dev/2001-August/000338.html http://www.mars.org/mailman/public/mad-dev/2002-May/000631.html http://www.mars.org/mailman/public/mad-dev/2002-May/000634.html
Cheers, -rob