Re: [Live-devel] Play out PCR from gettimeofday rather thaHi Ross,
Thanks for your reply. You are quite right, the PCR is always more accurate
straight out of an encoder, so I have shelved that desperate idea which as it
turns out wasn't a problem anyway.
I have been inspecting the clips produced by our Bitpack encoder and they do
indeed have the discontinuity_indicator set on the first video packet, so there
are no CC errors or PCR problems on our PID273, being video.
However, when we change clips, we are registering CC errors on PID 0, 64 and
40, being PAT, PMT and Audio respectively. Should the first packet in the
clips for these pids contain an adaptation field with discontinuity_indicator
true also?
Incidentally, when I was chasing the PCR accuracy 'problem', I have noted that
under default settings for MAX_PLAYOUT_BUFFER_DURATION (being 0.1s) the PCR
jitter is seen at about 35ns, and we do from time to time experience
pixellation at broadcast output, however when I reduce this buffer to 0.01s,
the jitter is reduced to 16ns and any pixellation during clip playout is gone.
I don't understand why that setting should affect the packet presentation
timing as the naming of that var would imply to me the length of a FIFO more
than anything else.
To solve this clip change problem I am now leaning toward the idea of keeping
an array of incrementing CC per PID, and playing that out - OR, if the non-PCR
carrying PIDs should have the discontinuity_indicator flag when they first
occur in a clip, inspecting the clips and adjusting them accordingly.
Looking forward to your comments,
Thanks,
-Tim
----- Original Message -----
From: Ross Finlayson
To: LIVE555 Streaming Media - development & use
Sent: Tuesday, March 22, 2011 1:00 PM
Subject: Re: [Live-devel] Play out PCR from gettimeofday rather than source
stream?
I see that timeNow is already stood up in in MPEG2TransportStreamFramer.cpp
- is there a quick and dirty way to insert PCR based on this time, at time of
playout, rather than pass through the source PCR?
No, not really, and this is a bad idea anyway. The PCR values that were
inserted in the files at the time that they were encoded will always be more
accurate (and better for decoders to use) than values derived from
'gettimeofday()'.
Instead, you should make sure that your TS files have the
'discontinuity_indicator' flag set at the start. Our
"MPEG2TransportStreamFramer" code recognizes this flag, as should the decoder
in your STB.
--
Ross Finlayson
Live Networks, Inc.
http://www.live555.com/
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