[vlc-devel] Re: Re : VLC behavior

Jean-Paul Saman jean-paul.saman at planet.nl
Tue Nov 8 21:57:27 CET 2005

adrian hornsby wrote:
>>>hornsby wrote:
>>>Hi everyone,
>>>What would be VLC behavior if in a MPEG2 TS stream,
> one full GOP is
>>>?? would it be able to resyncro without any
> artifacts on the screen ??
>>If the first frame is an I-frame, then there won't
> be any 
> artefacts.
>>Kind greetings,
>>Jean-Paul Saman.
> Hi Jean-Paul,
> Thanks for your answer. The problem is that a GOP ,in
> display order, never start with I frame but usually
> with a B frame. So VLC receive first an I frame then
> the B frame,  but reorder it, right ? Can vlc lose a
> bit of info ??
I think you are wrong. An I-frame is a selfcontained frame, a B-frame 
depends on other frames in 2 directions, a P-frame depends on an other 
frame only in one direction. The typical sequence a GOP or series of 
frames is sent is:


The B-frames are always sent before they are actually needed, but after 
the first I-frame of a GOP.

> The thing is that I did the test, and some very little
> artifact appears on the screen, few scares. 
> My attention is to test my splicing tool with VLC. I
> use beginning and end of GOP as splicing points. But
> of course I had to try with the exact same stream
> first. So i only remove one GOP from the stream and
> see VLC's behavior.
> You can use my tool to see yourself. Of course, VLC is
> so good that I tend to think the problem is in my tool
> but I checked everything and I couldn't find any
> explanation.
> My tool is build on live555.com library. You can
> download my tool from here. 
> Just compile it and play the "testRelay" file in
> /testProgs/ directory.
> testRelay work on command line as follow :
> ./testRelay <input_multicast_address1> <port1>
> <input_multicast_address2> <port2>
> <output_multicast_address1> <port1>
> (i.e:./testRelay 4444 4444
> 1234)
> to ask splicing, press the key "s", to stop "q"
> The splicing tool is in the liveMedia directory :
> -MPEG2TransportStreamSplicer.cpp
> Thanks so much for helping me.
> Best Regards,
> I want to release a Real Time splicing tool on GPL, if
> you want to help me with little thing, please email
> me. I would really like having experts helping me.
> adrian

Jean-Paul Saman.

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