Re: MPEG movies & frame rate

[horace.mitchell(at)gsfc.nasa.gov]

Niclas,

    You may be able to do this by writing the MPEG file (I assume we're
talking MPEG1 here), closing it,  then fixing the header of the file to
reflect a different frame rate.  I've done this myself and can give you IDL
code that may work.  I use it to fix MPEG aspect ratios since IDL does not
handle the MPEG aspect ratio correctly in IDL 5.3.

However, you should be aware that there are only a limited number of MPEG1
frame rates.  The possibilities are:

 rates = ['23.976 frames per second', '24 frames per second', $
           '25 frames per second', '29.97 frames per second', '30 frames
per second', $
           '50 frames per second', '59.94 frames per second', '60 frames
per second']

If you are looking to slow the animation down to 15 frames per second or
slower, you are out of luck.  Also, the frame rate has very little to do
directly with the size of the file.  Every MPEG animation has a bit-rate
which determines how many bits the animation delivers per second.  If you
reduce the frame rate or the image size and leave both the bit rate and the
duration the same, the file size of the animation is unchanged.  Of course,
the quality of the animation may suffer.

Hope this helps,

Horace


Niclas H M Tylli wrote:

> I have managed to stream the IDL graphics window content to a mpeg movie
> file according to the help file sample; I use version 5.1. However, to
> the best of my knowledge (which, being a newbie, doesn't account for
> much ;-) there is no way to influence the frame rate. An obvious work
> around would be to loop the same image for a number of frames, but then
> the resulting movie is unnecessarily big.. Does anybody have some
> pointers on how to get around this in a more elegant way?
>
> TIA,
> niclas