[ID3 Dev] Calculating playback duration and bitrate

[Wan-Hi]

hello again.

i wonder if anyone knows a good resource where i can learn more about 
how to calculate playback durations and bitrates of mp3 files. i tried 
search machines like google, but i couldn't find out anything useful.

i know the mp3 standard is not free and obtaining detailled specs from 
the owner (who's the owner anyway? frauenhofer or the MPEG consortium?) 
would be expensive. i'm doing this just for a hobby project and think 
that would just be overkill to get the whole specs. moreover i don't 
intend to read out the complete data from a file but only some specific 
infos. the reason why i ask you guys is because i think that some of you 
might have worked on that subject as well.

if i comprehend correctly, calculation of playback duration and bitrate 
can be achieved by parsing all mp3 frame headers. but this appears to be 
a costy method to me. usually audio players retrieve these basic infos 
in less than half a second (i know, quite a non-general impression), so 
there seems to be a quicker way.

i've went over to xiph.org and found their win32 lib quite useful for 
ogg vorbis files because it inherits everything to obtain information 
from an audio file. is there something similar for mp3? the ms windows 
media format sdk does do the things i'm interested in, but it has some 
disadvantages that bother me.

wan-hi


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