[MEncoder-users] Conversion to FLV, are my settings optimal?

[Francis Rammeloo]

Thanks for your very interesting post. I did a few experiments yesterday,
and it seems that your settings produce a video of similar quality and with
a smaller fizesize. So that's very interesting already. Some mp4 videos
failed however, I don't understand exactly why, but I'll figure it out
eventually. I'll do some more experimenting.

Thanks again for your detailed reply. You're probably helping a lot of
people with this.

Grtz,
Francis

2008/12/4 David Smith <dcsmith2 at gmail.com>

> >
> > I am writing a desktop video uploader application that allows the user to
> > upload any movie to the video section of our website. The web-player is
> > made
> > in flash, like on YouTube. So the output format must be flv, and not too
> > big
> > to avoid overloading the server. These are the settings that I use
> > currently:
> >
> >
> > input.avi
> >
> > -ofps 12
> >
> > -o mp3lame
> >
> > -lameopts abr:br=56
> >
> > -of lavf
> >
> > -srate 22050
> >
> > -vf softskip,decimate,pp7,scale=480:320,hqdn3d=4:3:6,harddup
> >
> > -ovc lavc
> >
> > -lavcopts
> >
> >
> keyint=15:vcodec=flv:vbitrate=256:mbd=2:v4mv:mv0:trell:vqcomp=1:vrc_eq=(tex+10^8*mcVar)^0.1:vstrict=-1
> >
> > -o output.flv
> >
> >
> > Do you see any room for improvement here?
> >
> >
> > I'd greatly appreciate any feedback.
> >
> >
> > Thanks,
> >
> > Francis
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> > MEncoder-users at mplayerhq.hu
> > https://lists.mplayerhq.hu/mailman/listinfo/mencoder-users
>
>
> It really depends on your application, but if you are just doing video
> convesion of typical file formats into FLV then your command line looks
> way overly complicated.
>
> The things that look like they can go away are:
>
> *softskip,decimate,pp7,hqdn3d=4:3:6*
>
> and
>
> *mv0:vqcomp=1:vrc_eq=(tex+10^8*mcVar)^0.1:vstrict=-1
> * You are just making your server work harder to convert the video for
> almost no dicsernable improvement in video whatsoever. I have experimented
> endlessly with mencoders Flash conversion, testing to see if some of these
> random switches make any difference in quality and they don't, trust me.
>
> What I have learned is that doing a 2-pass conversion is unequvilocally the
> best way to go.  *You should be doing 2 pass*.  You will get the most
> optimized file size, in combination with the best video quality.  This is
> how YouTube does it.  I have been able to replicate YouTube's file size and
> quality almost exactly using 2-pass.
>
> If you know for sure that every video should be converted at vbitrate=256
> then it's easy to do this programmatically.  The particular challenge I had
> was that certain videos coming in might be super low quality (like .rm
> files) or very high quality (.mov's).  So I had to set my vqscale to about
> 10, parse out the resulting bitrate, then stick that into the second pass
> since the second pass has to have a fixed bitrate to make any sense using
> it.  Fyi, I did all this on a PC using java.lang.Runtime under my app
> engine
> (ColdFusion) to parse the results.
>
> All that being said, here's the my basic command line syntax that I've
> found
> yeilds really excellent results in terms of file size, quality and
> processing time using the two pass scenario and a fixed rate:
>
> PASS 1:
> input.avi -o output.flv -oac mp3lame -lameopts q=9:mode=3 -srate 22050 -ovc
> lavc -lavcopts
> vcodec=flv:vbitrate=256:mbd=2:trell:v4mv:last_pred=3:vpass=1:turbo -mc 1
> -ofps 30 -of lavf -vf harddup -nosound
>
> PASS 2:
> input.avi -o output.flv -oac mp3lame -lameopts q=9:mode=3 -srate 22050 -ovc
> lavc -lavcopts vcodec=flv:vbitrate=256:mbd=2:trell:v4mv:last_pred=3:vpass=2
> -mc 1 -ofps 30 -of lavf -vf harddup
>
> Note that I am using -nosound on the first pass.  This speeds things up
> considerably since you don't NEED to convert the audio twice.  Since
> -nosound cancels the conversion I didn't bother removing the -oac line from
> pass 1 (it might even be required but I forget).
>
> The -ofps is really your choice.  For me 30 works great almost all the
> time.
>
> I don't think you need to be using -softskip unless you plan to be using
> advanced filters (inverse telecine, temporal denoising, etc.) or stuff with
> DVDs.  For "regular" video formats it does not seem to make a difference
> except to slow down the processing speed.
>
> Also, you will notice I decided to use an audio quality level of 9 instead
> of a fixed rate, and a mode=3 which is mono.  Let me just tell you that
> most
> people watching video on the web cannot tell the difference between mono
> and
> stereo, and this will in fact will get you a much smaller file size while
> increasing your processing speed.  This was ultimately the way I was able
> to
> get my converted files to be about the same size and quality as youtube.
>  If
> you stay with stereo you will be doubling the audio portion of your file
> size (if that matters to you).  In my case, I have to pay for every bit of
> bandwidth used, so I was focused heavily on reducing file size, but of
> course still keeping a high enough quality video.  Again, YouTube was my
> benchmark.  You can do whatever.
>
> I hope this helps.  Just experiment constantly until you find your own
> personal happy-medium.  Everybody's conversion techniques are highly
> specific to the application.  Mine was based on a YouTube benchmark, and
> having no control over the type or size of input video.
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