[vlc-devel] MPEG2 GOP handling and TS discontinuity

j.zorko at att.net j.zorko at att.net
Wed Aug 27 00:28:35 CEST 2003

Hello, all ...

I've a question to ask -- i'm still studying the PS-to-TS code, but I wanted to ask this now.  
Some of this may be more appropriate to the libmpeg2 dev list, but since VLC is responsible for 
feeding libmpeg2, I thought it would be of interest here as well.

Basically, how does the TS discontinuity relate to MPEG2 GOP handling?  Assuming the TS 
header is properly filled out to indicate a discontinuity after a seek on the PS happens, and the 
client can properly identify a TS discontinuity, what is VLC supposed to do?  The options I see 

1. on the client VLC, don't decode / display anything until we're at an I-frame (but this only 
works for closed GOPs ... open GOPs -- GOPs with P and B frames that reference frames in 
earlier GOPs, could still pose a problem)
2. on the server VLC, don't seek until we've read an entire GOP i.e. when told to seek, just set a 
flag, and inside whatever pf_read() points to, wait until we've read an entire GOP before looking 
to see if this flag is set, then and only then calling input_Seek() if so ... again, this sounds like it 
would fall apart on open GOPs

It seems open GOPs are quite the issue ... when seeking to an arbitrary position in the PS, how 
can we be sure the place we're seeking to has no references to areas in the PS that we may have 
skipped because of the seek?



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