[GRASS-user] r.out.mpeg... how to change number of frames per second....

[Hamish]

Andranik wrote:
> > I am using r.out.mpeg to make animation from a series
> > of calculations of NDVI, but as there is no way to change
> > the interval between the first view will change to second
> > and so on, my video takes only a few seconds and is passing
> > to fast to notice something...
> > I want to make 1 or 2 views per second. Is it possible
> > to do?

Markus N:
> I am not sure that r.out.mpeg supports this.

I'm pretty sure it doesn't. AFAIR MPEG-1 can do it, but perhaps
only with a fixed choice of the common NTSC/PAL 24-30fps rates?

In the past I've found MPEG-1 playback needed a player with
frame rate override (like mplayer) to stop it from running
at 24~30fps. I think the intermediary text control file which
r.out.mpeg creates can be edited for a re-encode, if it is
not deleted. Another idea is to just create 24~30 fps (symlinks
created by a script work well here) and save to a DVD. MPEG-1
quality is so bad by comparison to modern codecs, that the only
things left going for it is it's unqustionably 100% free to use
and the convinence of the r.out.mpeg module + ubiquity of the
ppmtompeg encoder from NetPBM. See the r.out.mpeg man page for
suggested playback program (an old X-windows thing) if all else
fails.


> For better ways of producing animations, please see:
> http://grasswiki.osgeo.org/wiki/Movies

FYI, I've just added notes to that page on how to encode as
WebM format (VP8 codec) using the reference encoder. It is
the nearest thing we have to H.264 in quality, but can be used
unencumbered. Anyone with Firefox, Opera, or Chrome web browsers
already has a playback program installed. It's the new YouTube
native format, and new Wikipedia video uploads require it AFAIK.

I promote it partly because we can encode to it without legal
worries, and partly because lately all the x264 .avi encoding
I've tried with mencoder using the rules on the wiki Movies page
get stuck on the first frame when played back with VLC*. :)
(but mplayer playback goes fine)

[*] actually it works via the VLC plugin in Firefox, but not the
standalone player. Maybe it's because my GRASS animations are too
short to get to the second keyframe or something? I'm not sure.


Seeing all the problems we've had with keeping up with FFMPEG's
api changes* from NVIZ, maybe we should look at raw png/ppm
frames + the option to system() call the webm encoder on them
as a simpler and more robust alternative.

[*] fwiw Debian has just dropped ffmpeg for the more stability-
focused libav fork, for the same endless api-catch-up reasons.


good luck,
Hamish