[Live-devel] RE : Re: bug found and corrected

[roor0735-ml at yahoo.fr]

I agree, it is not really a bug. In fact, your library is used to stream live DVB-T MPEG2 Transport stream in real-time over the network. So, I think it will be hard to calculate indexes before streaming the recording TS files. 
Concerning the proposed changes, I try to find a better way to correct the packet duration estimation issues. Normally, the PCR should be annouced with a quite regular periodicity. If the packet interval between two PCR annoucement is too low compared to the mean periodiciy of the PCR, then the PCR must be ignored   in order to not introduce errors in the packet duration estimation. So, I introduce a 
new constant called PCR_PERIOD_VARIATION_RATIO that adjusts the minimum and tolerated packet interval from the mean PCR announcement period.

For instance, in my sequence, the mean period of PCR announcement converges to around 47. The ratio is set to 50%, so the minimum packet interval between two PCR is 23.  I think this method is less arbitrary than the "20" value.

I hope this can help people that wants to broadcast VBR multiplexed dataflows.
Regards,
Romain


Ross Finlayson <finlayson at live555.com> a écrit : Thanks.  However, the existing code is not really a 'bug', although 
your suggested change is (arguably) an improvement.

As you noticed, the current per-transport-packet duration estimation 
code has trouble converging on a stable estimate for streams - such 
as yours - that are wildly VBR.  Your suggested change will probably 
help things (although I can also imagine streams for which it might 
make things worse by taking longer to converge to the 'correct' 
average duration).  I am also a bit concerned about the arbitrariness 
of the constant "20" that you use.

Nonetheless, I'll add your change to the next release of the library.

(Looking longer-term, a better solution for streaming prerecorded 
files (but not live streams) will be to extend the existing "index 
file" mechanism to include accurate durations - which could be 
computed in advance when generating the index file.)


 Ross Finlayson
 Live Networks, Inc. (LIVE555.COM)

   
       
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