[x264-devel] Re: encode for streaming

[Alex Izvorski]

On Fri, 2007-04-27 at 15:02 +0200, Jindrich Makovicka wrote:
> On 4/27/07, DNA Studios s.r.l. <info at dnastudios.it> wrote:
> > Loren Merritt ha scritto:
> > > On Thu, 26 Apr 2007, DNA Studios s.r.l. wrote:
> > >
> > >> I have a Video on demand platform, I use Darwin streaming server and
> > >> vlc or mplayer as client (sometime ffmpeg directly).
> > >> Usually I encode my movies in main profile (1 pass average bitrate
> > >> 1000 Kbit/s).
> > >> There are some parameters to use (or to do not use) for streaming
> > >> purpose? (i.e. B-frames number or keyframe interval)
> > >
> > > The main options that differ between streaming and other encoding
> > > types are: --keyint, --vbv-maxrate, --vbv-bufsize.
> > > However, I can't tell you what values you should give those options,
> > > other than to say that they're the same in any streaming codec and not
> > > specific to x264.
> > >
> > > --Loren Merritt
> > Thanks for answer,
> > Let me make just another question:
> > vbv-bufsize override the player cache settings when streaming?
> > If I encode with vbv-bufsize 2000Kbit and I play it with a player that
> > have 1000Kbit of cache setting?
> 
> No, it controls only the rate control behavior on the encoder side. If
> you exceed the player cache size, you can expect stuttering and/or
> audio-video desynchronization. You should set the buffer size as the
> minimum of expected player buffer sizes.

Interestingly enough, in the case of H264 in MPEG2 transport/program
streams, the H.222 amd 3 spec explicitly says a decoder must use the
largest possible buffer for the level of the stream, unless a different
size is specified in the hrd_parameters() headers which are part of the
VUI which is in the SPS.  (this is clause 8e in the ammendment, which
changes 2.4.3.7 in the original).

I don't know whether hardware/software decoders respect this.

I would like to add the ability to generate VUI headers at some point,
so perhaps we'll find out.

Regards,
--Alex


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