[FFmpeg-devel] Sponsoring feature for H.264 decoding with scaling factor (1/2, 1/4...) (if possible)

[Eric Beuque]

2016-06-20 0:35 GMT+02:00 Ivan Kalvachev <ikalvachev at gmail.com>:

> On 6/17/16, Eric Beuque <eric.beuque at gmail.com> wrote:
> > 2016-06-17 19:16 GMT+02:00 Michael Niedermayer <michael at niedermayer.cc>:
> >
> >> On Fri, Jun 17, 2016 at 05:39:23PM +0200, Eric Beuque wrote:
> >> > Hi,
> >> >
> >> > i'm posting here for a feature that is missing in ffmpeg (or may be i
> >> > missed something), which consist of decoding H.264 frame with a
> scaling
> >> > factor of 1/2, 1/4, 1/8...
> >> >
> >> > I found the parameter lowres, which works well with MJPEG stream but
> >> > it's
> >> > not working with the H.264 decoder.
> >> >
> >> > I don't know if it's something possible to implement in the decoder,
> but
> >> if
> >> > yes, my compagny agreed to sponsor the feature (depending on the cost
> of
> >> > course), if a developer qualified is interested to do it.
> >> >
> >> > Is someone know if it is possible, and if it can exist someone
> >> > interested
> >> > to develop this feature?
> >>
> >> is it acceptable if the encoder enforces some restrictions on the used
> >> features ?
> >>
> >> most general h264 likely cannot efficiently be decoded in lower
> >> resolution with acceptable quality
> >> Restricting the used intra modes may make it possible to do it though
> >> i dont know what the quality would be but better than without
> >> restrictions
> >>
> >> [...]
> >>
> >
> >
> > Actually, the main goal is for motion detection algorithm, so we need
> small
> > resolution and best quality is not required. We just need good estimation
> > for the moving pixel.
> >
> > For now, we decode in H.264, and scale it close 320x240, the then we
> > perform motion detection on it. The goal is to speed up the process and
> > reduce the memory usage since decoding a 2048x1536 picture lead around a
> 5
> > MB for the decoded image in memory.
>
> Have you tried to extract the motion vectors of the H.264 stream itself?
>
> If the encoder supports more than I-frames, it should do some Motion
> Estimation.
>

No, but i don't really know how it is working. Our goal is to split the
picture in 1024 block and telling which block has motion detection or not.
Do we have a motion vectors for the I-Frame it self? I assume no, but i
actually need motion detection in any frame.





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