[MEncoder-users] Need some hints for my tv recording concept

[Martin Collins]

On Sun, 28 Aug 2005 10:57:11 +0200
Gerhard Brauer <gerhard.brauer at web.de> wrote:

> A) record at 352x288
> These are the parameters for my mencoder record script:
...
>  vcodec=mjpeg:mbd=1:autoaspect:abitrate=128:acodec=ac3:mv0:nr=10"

mbd=2 is better if you're machine is fast enough. nr=10 is a bit
low but whatever works for you. ac3 seems an odd choice, I would
just use pcm and save the cycles for the video. If disc space is tight
mp3 might encode quicker than ac3.

> So i reencode the video later on a faster pc after recording where i
> must not care about real time things:
> 
> -vf pp=de,scale=704:544,denoise3d -oac copy 
> -ovc lavc -lavcopts vcodec=mpeg4:mbd=1:aspect=4/3 -sws 1
> -ffourcc divx

Scaling up when encoding is a complete waste of time and bits. You
have also munged your aspect ratio here. Denoising should be first
in the chain, but probably stick with nr rather than denoise3d.

> And here i have some questions:
> 	a) scaling the low source video to a bigger size, isn't this
> 	not something like "interpoling" by low-budget scanners? My
> 	thought was that software scaling may have a better quality
> 	then later scaling in real time by hardware?

It is like interpolating so you should only do it on playback, whether
by software or hardware. No point in storing all those invented
pixels.

> 	b) Are there filters,one/two pass runs or any other
> 	parameters,things you would do? I tested a lot but mostly i do
> 	not see a real difference.

Two pass encoding will reduce the size for a given quality level or
increase the quality for a given size. Have you read the encoding-tips
document?

> 	c) The -ffourcc option. Is it correct that lavc with
> 	vcodec=mpeg4 produce a divx coded video? All my linux player
> 	accepted the coded videos but on a friends windows pc (with
> 	vlc player) it wouldn't play. Only until i use the above
> 	-ffourcc with divx or DX50 he could play it. So: is this
> 	option rather a cosmetic entry in the header or do i really
> 	change the codec by setting/changing this parameter?

It is cosmetic, the (new) default fourcc is just not widely recognised
yet.

> But i'm curious about getting some hints to do it better or in an
> other way.

I would capture full height and as much width as possible, without any
filters or fancy flags to slow things down. Set aspect appropriately.
Do any processing you want when you play back or re-encode.

Martin