[vlc-devel] Re: Doing an lseek() with VOB files ...

Jean-Paul Saman saman at natlab.research.philips.com
Wed Aug 13 10:27:44 CEST 2003

John Michael Zorko wrote:
> Jean-Paul,
> Thanks for your input.
>> Does the server VLC start streaming on a I-Frame when doing ff/rewind? 
>> If not you get a jumbled-up video because you then have either a P or 
>> a B-Frame and they depend on previous frames.
> The server does an input_Seek() to the off_t of a sequence header / 
> GOP.  Since I-frames are the first frame in the GOP, this shouldn't be 
> an issue.  The real issue here is that, when VLC is playing from a file, 
> seeking anywhere doesn't disrupt the video i.e. the seek bar in the GUI 
> does not seek on I-frames, it seeks to an off_t that represents where 
> the GUI bar was moved to, without regard to if this is an I-frame or 
> not.  When playing from a stream, this same action (using the GUI seek 
> bar on the server VLC) results in momentary disrupted video on the 
> client VLC.
Does the server set the TS discontinuity bit when doing ff/rewind on the 
first packet (PCR packet AFAIK) it can? Because the server needs to tell 
the client that a timing gap occured.

> So, something is different when VLC is playing from a file and a seek 
> happens, than playing from a stream and a seek happens on the server 
> VLC.  Either the data sent from the server to the client is different in 
> this case, or the code that the client VLC executes (the UDP access 
> module, the MPEG demuxer, the libmpeg2 codec interface, and the 
> video_output) is doing something different because it's a stream, and 
> this something different is resulting in jumbled video for a fraction of 
> a second every time the server VLC seeks, whether it's to an I-frame, 
> GOP, sequence header, pack header or random off_t.  This is what i'm 
> trying to find.
 From file you read a MPEG2-PS (I guess) and from the server you read an 
SP-TS. This SP-TS goes into the ts_dvbpsi (or ts) demuxer and then to 
the ps demuxer. While the file goes directly into the ps demuxer.
Kind greetings,

Jean-Paul Saman

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