[MEncoder-users] issues for time-lapse video encoding
Hugh Secker-Walker
hsw at hodain.net
Tue May 19 00:12:51 CEST 2009
Hi Folks,
I'm creating and processing time-lapse movies of outdoor scenes using
mencoder (or ffmpeg) to do the capture from a webcam, and then
mencoder to process into a playable video. I'm using an Ubuntu server
setup, and the initial video comes in from a USB webcam in
video4linux2 format. I'm capturing 1280x1024 frames at 0.1 frame per
second, i.e. 6 frames per minute. The intended playback is 30 fps.
I have two questions:
1) Since I want to use two-pass processing of the captured video, I
need to do the initial capture with as little degredation as
possible. I'd like e.g. 3000 frames to go into about 1gB in the
oringial captured video. Is there a recommended codec/setting for
this? I've tried rawvideo and ffv1, but these generate too much
data. So I need some compression. Given that the size of the
compressed video at this point isn't a big issue, which codec will
degrade the images the least or have the simplest behavior/results?
BTW, I'm currently using the mjpeg codec, but there's no control
that I can see (ffmpeg) for the compression that it's doing....
2) I want to do some filtering of the resulting video. In particular,
it would be nice to remove all the objects, e.g. birds, that appear
in only a single frame. I can imagine that some sort of median
filter would do the job (e.g. median for each pixel across 7
frames). What should I be looking at for this kind of filtering?
It's a kind of denoising, but the extent of the noisy object can be
quite large, but always only for a single frame.
Relatedly, is there a codec that would be best suited to the
time-lapse material? I've toyed with wmv2, mpeg4, and x264 -- but
experimenting with just the set of controls that I've seen
mentioned in FAQs is daunting, and I haven't yet seen anything that
specifically addresses the nature of time-lapse video of outdoor
scenes. So, I'd also appreciate any pointers to information about
the encoding issues for time-lapse video.
Thanks in advance,
-Hugh
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