[Ffmpeg-devel] Resize on the fly
Tue Oct 25 12:06:52 CEST 2005
On Tue, 25 Oct 2005, Andy Parkins wrote:
> I'd like to be able to resize an mpeg4 stream on the fly. It wouldn't be an
> arbitrary scale, just half, quarter, eighth, etc. What I'd like to do is
> keep a master, high-resolution stream on disk, but be able to stream a
> smaller resolution without having to do a full decode-resize-encode cycle.
> I'm curious as to whether this is a crazy thing to even attempt? For example,
> could one just throw away half the macroblocks, change some numbers in the
> header and get a useable stream? The little I know about MPEG4 makes me
> think that the answer is "no", but I thought I should ask some people who
> know what they're talking about :-)
You can decode the original stream to a lower resolution, thus reducing
decode time and eliminating the scale step, but not saving any bandwidth
(see -lavdopts lowres).
You can't create a new mpeg4 stream at reduced resolution (scaling
or cropping) without a full re-encode.
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