[vlc-devel] Problem Understanding Splicing Issues

hornsby adrian_hornsby at yahoo.co.uk
Wed Oct 26 16:12:56 CEST 2005

Hi everyone,

I have developed a Splicing Tool to splice in real time any MPEG2-ts streams.
The basic idea behind it is to test several decoding issue to be able to 
specify requirements for an adaptive decoder and also to use it as channel 
switching in a VLC based network TV system.
The splicing tool work as follow :
(UDP packets consist of 7 TS packets. So my buffer = 7 ts packets)

1- finding OUT POINT in 1st Stream (actually cutting just before beginning of 
new PES- so finding PES at position x, cutting at x-1)
if the end of PES isn't at the end of the buffer (position 7) modify PID of 
remaining packets in the buffer to PID 8191 (null packet)
Then, at position 6 and 7, insert PAT/PMT of the 2 stream.

2-send UDP packet 

3-finding IN POINT in 2nd stream (Finding beginning of new PES- moving new PES 
packet at the beginning of the buffer)

4-send UDP packet

analysing the streams with  DVDsnoop show exactly what expected
-----endPES ---><---PAT---><---PMT---><-------newPES------

Now I have some troubles !!
VLC manage most of the time to play and handle the splicing point without 
displaying issues. Sure, VLC complains about discontinuity packets as I do 
not (by purpose) arrange it but that isnt the problem. VLC also complains 
about DTS,PTS issues, timing break.

BUT, why most of the time VLC is able to handle it, and sometimes it 
doesn't ??? That I don't understand !!!! if it was a timing issue, it would 
happend ALL the time !!
VLC messages don't show any evidence in the difference of behaviour. Messages 
for "good" splicing are the same as for "bad" splicing.
VLC should be able anytime to handle this, as only PES header is needed for a 
decoder to start decoding pictures, right ??
I am missing something somewhere ???
I'd love you guys comment on that or give me some track where and how to 
isolate the problem because I'm lost.

The issue at the splicing point is the displaying of the cutting. Some scares 
appear on the video at the break.

you can download example of good splice and bad splice here :

THANKS So much for any help.


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