[FFmpeg-user] Nvidia GPU [was (no subject)]

[Tom Evans]

On Thu, Dec 15, 2011 at 6:42 PM, Lou <lou at lrcd.com> wrote:
> * The D in VDPAU stands for Decode, so it don't help the actual
>  encoding, and it doesn't use the GPU, but an onboard acceleration
>  chip, IIRC.
>
> This is a subject which I am somewhat unfamiliar, so others may want to
> add more accurate information or correct me.

I believe the decoding (or at least part of it) is offloaded onto the
shaders*, and hence performance will differ from card to card,
depending on the speed and number of shaders.

I've done a little playing, and it seems like** ffmpeg can only use
vdpau to display video, not to accelerate the decoding of the source
when transcoding, as it cannot read the decoded image back from VRAM.
I was trying things like this:

> $ ffmpeg -y -c:v h264_vdpau -i f1_2011_bahrain.mkv \
----> -frames 1000 -c:v libx264 -profile:v main -s 480x272 -aspect:v 480:272 \
----> -c:a libfaac -ac 2 -b:a 128k \
----> f1_2011_bahrain.iphone.mp4

Cheers

Tom

* As always, it is more than possible that I am spouting nonsense,
this is all 'IIRC'
** See above