[Live-devel] TransportStreamFramer latency?

[Morgan Tørvolt]

I see. Thanks. Wish me luck =)

-Morgan Tørvolt-


On 8/31/05, Ross Finlayson <finlayson at live.com> wrote:
> At 02:16 AM 8/31/2005, you wrote:
> > > For a custom project (using only the Amino STBs as client), we
> > > overcame this problem by modifying the "MPEG2TransportStreamFramer"
> > > by continually adjusting the computed "fTSPacketDurationEstimate"
> > > value in order to maintain a roughly fixed (and >0) estimated buffer
> > > size at the client.  Unfortunately, this code isn't very portable
> > > (because it's peculiar to the ideosyncracies of the Amino STB), so
> > > it's not clear if/when/how it could be made part of the general,
> > public code.
> >
> >Could you lend me an hand figuring out how to do this? Do you use
> >feedback from the STB?
> 
> No.  The STB receives raw UDP only, and so doesn't send back any RTCP
> packets, or anything similar.
> 
> >  In that case, how? I cannot see any function in
> >the stb that gives that kind of feedback.
> 
> There isn't any.  Instead, we *estimate* how much extra data is
> buffered at the client, and insert a 'fudge factor' into the
> calculation of "fDurationInMicroseconds" in order to keep the amount
> of estimated buffered data roughly constant.
> 
> I.e., the statement
>          fDurationInMicroseconds
>      = numTSPackets * (unsigned)(fTSPacketDurationEstimate*1000000);
> becomes
>          double fudgedPacketDurationEstimate = fTSPacketDurationEstimate;
>          if (clientBufferTimeEstimate < desiredBufferTime) {
>                  fudgedPacketDurationEstimate *= 0.9;
>          } else {
>                  fudgedPacketDurationEstimate /= 0.9;
>          }
>          fDurationInMicroseconds
>      = numTSPackets * (unsigned)(fudgedPacketDurationEstimate*1000000);
> 
> Where "clientBufferTimeEstimate" is our estimate of how many seconds
> worth of extra data is currently buffered at the client.  It is computed as
>          clientBufferTimeEstimate = estimatedTransmitTime - estimatedPlayTime;
> where "estimatedTransmitTime" is computed by adding up
>          fDurationInMicroseconds/1000000.0
> each time round the loop, and "estimatedPlayTime" is just the most
> recently-seen SCR.
> 
> Apart from this, the "MPEG2TransportStreamFramer" code remained the same.
> 
> 
> 
>         Ross Finlayson
>         LIVE.COM
>         <http://www.live.com/>
> 
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