[linux-audio-user] AC3 file structure question

I have a large AC3 file:

$ file chicken.ac3
chicken.ac3: ATSC A/52 aka AC-3 aka Dolby Digital stream, 48 kHz,,
complete main (CM) 3 front/2 rear, LFE on,, 448 kbit/s reserved Dolby
Surround mode

I want to create a much smaller file with the same parameters, ideally
silent, with a duration of about 2 sec, then concatenate the small file
at the beginning of the existing large file.

If I'm not mistaken, an AC3 file is made out of independent frames of
fixed size. Is that correct? If yes, what is the size of a frame?

If the frames are fixed-size, I could simply use dd to generate a small
fragment out of the existing file, then use cat to glue the fragment and
the original file.

-- 
Florin Andrei
http://florin.myip.org/