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

[Ivan Kalvachev]

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.