[FFmpeg-devel] UDP constant bitrate feature (cbr)

Michael Niedermayer michael at niedermayer.cc
Wed Nov 18 18:03:23 CET 2015

On Tue, Nov 17, 2015 at 03:06:27PM -0800, Zach Swena wrote:
> Hi Pavel,
> I can confirm that there is a problem with the UDP packet engine in
> FFmpeg.  FFmpeg has excessive jitter in it's UDP streaming output to the
> point where hardware decoders can't handle it.  My solution was to buffer
> to disk and have my own program read and send the datagrams via a very
> tight event loop.  While increasing the PCR period is not a bad thing,
> FFmpeg really should stream at a more consistant rate.  Can someone explain
> the theory behind how the UDP rate control is currently implemented in
> FFmpeg?  PCR sounds like a good way to tell when to send a packet, except
> not every packet contains one.  If FFmpeg uses PCR to tell how long to wait
> to send a packet, then do the packets in between go at line speed?  I plan
> on taking a look at the code that does this, but I would really appreciate
> it if someone who knows the code could explain the theory as I usually deal
> with a slightly different dev setup.

i suggest you read the mpeg specs, they detail when things should be
sent down to each byte IIRC
also IIRC its not that complicated, more like timestamp + bytepos/rate

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I know you won't believe me, but the highest form of Human Excellence is
to question oneself and others. -- Socrates
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