[MPlayer-users] encoding questions

[Matthias Czapla]

On Fri, Feb 06, 2004 at 06:14:37PM +0100, Amadeus wrote:
> I have a final question:
> 
> A DVD is encoded with 9000bps in mpeg2 format.
> Are there a rule of thumb what a mpeg2 bps does correspond to in mpeg4
> bps?

To my knowledge that is entirely dependent on the size in pixels, framerate
and content of the movie. Given a bitrate in bits per second for the MPEG4
file with a horizontal resolution of hsize pixels and a vertical resolution
of vsize pixels and the framerate in fps, the value of

bitrate / (hsize * vsize * framerate)

should be greater than 0.15 (at least this is enough for me most of the
time, some will suggest a value greater than 0.2, YMMV). I start with the
desired final filesize, which is 700MB most of the time, and the length of
the movie (say 6000 seconds). This gives a bitrate of
700 * 1024 * 1024 * 8 / 6000 = 978671 bps. Assuming the audio will be MP3
with 112kbps I subtract 112000 and get a bitrate of 866671bps for the video.
Then I try various resolutions (combinations of hsize and vsize) until I
find a suitable size to rescale the video to. HTH

Regards
Matthias