[vlc] VLC and MP3 streaming ...

[j.zorko at att.net]

Hello, all ...

I've been studying the VLC source for a few days now, and i'm getting a handle on how it does its' 
magic.  I'm still struggling with a few things, though, so if anyone who is familiar with VLC source 
code (especially VLC acting as a receiver of a MP3 multicast stream) I would appreciate some 
guidance.

OK -- VLC, when acting as an MP3 server, uses PacketizeThread() in modules/packetizer 
mpegaudio.c to locate the MP3 frame headers in the source and align packets on them.  This looks 
like standard stuff, similar to MP3 frame header code i've seen and written before.  However, i'm a 
bit confused as to why a PTS is associated with the packets -- is this for possible 
synchronization with another ES perhaps?  What i'm trying to do is implement a very basic fast-
forward / rewind mechanism, where the VLC acting as the MP3 server will just skip ahead n frames 
while the fast-forward or rewind is active (i.e. some button on some GUI).  I've successfully made 
PacketizeThread() skip n frames before sending one out (in a very experimental, hacky way i.e. 
calling GetChunk() multiple times at the end, suspecting that this advances the read pointer in the 
source content) and verified (using tcpdump) that only 1/nth as much data is sent by the VLC 
acting as the MP3 server.  However, the client VLC no longer plays the MP3 stream, so i'm trying to 
figure out why.  I suspect it has something to do with the PTS, but i'm not sure.  Can anyone with a 
better understanding of the way VLC decides what to play and what not to play of the packets it 
receives enlighten me a bit?

Regards,

John

--
Falling You - exploring the beauty 
of voice and sound
http://www.mp3.com/fallingyou








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