[MPlayer-users] Mencoder: Changing frame rate (RealMedia to vcd)

[RC]

On Fri, 31 Dec 2004 10:49:31 -0800
Bill Moseley <moseley at hank.org> wrote:

>    mencoder  -ovc lavc -lavcopts vcodec=mpeg1video \
>              -oac lavc -lavcopts acodec=mp2 \
>              input.rm

You'd get better quality doing 2-pass encoding, and adding at least
"mbd=2" and "trell" to your lavcopts.  Toolame provides much better
quality than the lavc mp2 codec.

You're likely unable to seek (backwards) in this file, as the keyframes
are only once every 250 frames by default, whereas the VCD standard is
30.

>    mplex -f 1 -o vcd.mpg temp.m1v temp.mpa

tcmplex (part of transcode) seems to produce smaller files, and screws
up less for me, but only minor differences.

> I don't see any advantage of using svcd since my source is only
> 320x240.

Well, players limit VCDs to stereo 224Kbit audio, whereas with SVCDs you
can use any bitrate, and mono/stereo/joint-stereo.  Plus, SVCDs use
MPEG-2, which is obviously better, and at higher (video) bitrates so the
picture can be much better.  

>  I assume I'd need to scale from the  Realmedia image size to vcd
>  images size (320x240 -> 352x240).
> Something like this?
> 
>    -vf scale -zoom -xy 352

No no.  There's no reason to use -xy or -zoom.  Just -vf scale=352:240
would work, although it will stretch your video.  A preferable option
would be "-vf expand=352:240" which will just add black-bars on the
sides (which you might not even be able to see on a TV screen) so you
have the right dimentions, and don't have to stretch anything.  Or, you
can up-scale the video to the right width, while maintaining the right
height:width aspect ratio, then croping the extra height, like this:
"-vf scale=352:-2,crop=352:240".  Take your pick.

> But how do I get the mpeg container instead of the avi which I can use
> for vcdimager?

You have several options.  You can just use "-of mpeg" which will give
you an mpeg instead of an avi, but vcdimager will have to pad it,
wasting a good 10-20% of your VCD disc space.  That's your easiest
option if you don't mind the waste.

If that's not acceptable, you can apply the version of the patch I've
attached, which allows you to use mplayer with "-dumpvideo" and
"-dumpaudio" on the file mencoder outputs, to create .m2v and .mp2 files
from your avi, which you can then use with mplex.

> 2) I have one .rm file that's encoded at 15fps.  -ovc lavc says it
> can't handle that fps:
> 
>    [mpeg1video @ 0x403b9008]MPEG1/2 doesnt support 15/1 fps
> 
> I can use -fps 30, but then the video is, obviously, fast.

The option you want is "-ofps" not "-fps".  And you might want to use
"29.97002997" instead of "30" to be within spec.
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