[FFmpeg-devel] [DOC] FFSERVER Configuration Files.

[Piero Bugoni]

>
> > > > 
> > > > > > +#  Settings:
> > > > > > +#
> > > > > > +# The Q	value is pretty important here. Values of around 5 to 7.5
> > > > > > +# give a reasonable compromise between stream width, and image quality.
> > > > > > +# Make sure to match the settings in this file with those on the command line.
> > > > > > +# in this instance values grater than 10 will probably make image indiscernable.
> > > > > > +#
> > > > > > +# Some additional settings for higher quality, but a fatter stream:
> > > > > > +#
> > > > > > +
> > > > > > +# Qmin/Qmax=1, vbr~=12000, vbuf=52(min)
> > > > > > +# Qmin/Qmax=2, vbr~=7100,  vbuf=33(min)
> > > > > > +# Qmin/Qmax=3, vbr~=5200,  vbuf=22(min) good quality/stream compromise
> > > > > > +# Qmin/Qmax=4, vbr~=4800,  vbuf=21(min)
> > > > > > +# Qmin/Qmax=5, vbr~=4000,  vbuf=19(min)
> > > > > > +# Qmin/Qmax=6, vbr~=3200,  vbuf=13(min)
> > > > > 
> > > > > constant qp encoding is not suitable for streaming over a channel with
> > > > > limited bandwidth
> > > > > 
> > > > 
> > > > OK.
> > > > 
> > > > (How limited)?  I have around 320Kb/s upload speed to the net.
> > > 
> > > you misunderstand
> > > fixed qp encoding IS fundamentally not suitable for streaming, it does not
> > > matter what bandwidth you have
> > 
> > Why is that?
> 
> because if you set qp high quality will be bad, if you set it low your
> bandwidth will be insufficient if the video has the wrong content
> your video might need the bitrates written above another might need 10x
> the bitrate at the same qp (and i mean same resolution and framerate)
> 
> 


> 
> use bitrate and maxrate (and maxrate at least 30% higher than bitrate)
> set qmin=2 qmax=31
> 
> [...]

I did not see a "maxrate" setting in the original ffserver.conf, so if it exists then maybe it is
MaxRate, otherwise this translates to something like this in the conf file:

VideoBitRate 
Would be set to that 30% higher value in the conf file, (maxrate), and the "bitrate" and "maxrate"
options would be used on the command line.

I never saw any video with a "Q" value over about 12 that I was ever interested in viewing. I
thought about stream qaulity and I presumed the setup would be used in a security-camera type
operation. If the video quality is not sufficient to positively id someone then it is pointles,
but does make for abstract art. 

I understand bitrate is content dependent. The fixed "Q" values give an indication of where to
start. I had run tests with a video that I figured changed enough, frame to frame. However, I
suppose encoding a video of white noise might give some indication of bitrate range.

So a range can be set down to the minimum viewing quality. 

I'll test some of this.

P.
  




       
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