[MEncoder-users] (work-in-progress) XviD encoding guide

[Oleynik Phil]

Vladimir Mosgalin wrote:

>Hi Phil Oleynik!
>
> On 2005.06.25 at 01:06:26 +0400, Phil Oleynik wrote next:
>
>  
>
>>*max_key_interval
>>Usually, no one will need it. However, in some cases scene changes
>>very rarely.  To save details sharpness one may try to lower its value
>>from default.
>>    
>>
>
>It doesn't do anything useful.
>  
>
Once, I have compressed very slow scene-changing animation with many 
details in scenes.
When I looked at graph of I/K-frames, I noticed that about 30 percent of 
them are just because
of timeout, not associated with real scene change. I set it to 500, file 
became smaller, some percents.

>  
>
>>*keyframe_boost
>>If you encode cartoon/anime, you will need it to get sharper edges
>>with the same bitrate.
>>    
>>
>
>You might add that recommended value is around 15, 10-20 for me.
>
>It doesn't really hurt on real life video, but doesn't help too. Great
>for animation, yes.
>  
>
I usually set it to 50 when source is of high quality, and result should 
keep the same level. On real video,
or when keyframes are very frequent, your value is more sane.

>  
>
>>*kfreduction
>>No human is able do distinguish how bad rapid flashing frames were
>>compressed, but it is hard task for codec. With this option only the
>>last frame from series of flashes will get full bitrate.
>>    
>>
>
>I don't really understand why, but a lot of people advice to use 24 for
>23.976/24/25 fps video and 30 (default) for 29.97/30 fps video.
>  
>
This is quality percent-divisor, 24 and 30 it is maybe for kfthreshold?

>  
>
>>*(no)packed
>>One of best XviD features, frame swapping. If this is turned on, codec
>>will try to swap frames in order to get more quality. Price here is
>>DivX compatibility.
>>*(no)closed_gop
>>This option also may break compatibility. However, it may save a few bits.
>>
>>    
>>
>
>One of this options (or both, don't remember) actually break lavc
>compatibility, it will display file with errors (maybe fixed in newer
>versions, but..). They may reduce file a bit, but it doesn't worth it.
>
>  
>
>>*qpel
>>Option, that should be used for high quality streams, it may do good,
>>or may do bad to your movie. Highly dependent from source material.
>>    
>>
>
>Maybe it was me, but I never found cases where it was useful - not with
>xvid, nor with lavc. The quality is always lower or at least the same.
>
>  
>
>>*gmc
>>Also, highly dependent from source material. If you have many
>>panoramic scenes, this will save a great amount of bits using XviD
>>pan/zoom compressing features. This will make your movie decode slower
>>(640*480 24fps pan scene may become too hard for Celeron III 800, my
>>own exp.)
>>    
>>
>
>Again, I tested it on a lot of material, it never helped.. though it
>doesn't usually waste a lot of bitrate too, so the picture stays about
>the same.
>
>But maybe it would help in very low bitrate cases, I never tested this.
>  
>
It helps great, when camera moves right-left-right-left-right... Slowly 
and with sense, i.e. interframes
are to be seen clear.


Philipp
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