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

[Tom Evans]

On Thu, Dec 15, 2011 at 9:12 PM, Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:
> Tom Evans <tevans.uk <at> googlemail.com> writes:
>
>> 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.
>
> ffmpeg does NOT support hardware-accelerated video (and audio) decoding.
>
> FFmpeg supports video player applications that use xVMC, VDPAU, VA-API or DXVA2.
> (None of those use the shaders, the decoding speed is not depending at all on
> the number of shaders, my GT520 which is a low-end card decodes H264 "faster"
> than any high-end card with ten times as many shaders. De-interlacing speed
> heavily depends on the number of shaders, but de-interlacing needs no libavcodec
> support.)
>
> Or in other words: libavcodec contains code that other applications can use to
> decode in hardware, ffmpeg (the application) does not use that code.
>
> Carl Eugen
>
> Disclaimer: I only know about PureVideo for VDPAU, it is possible that other
> technologies work differently (but I would be surprised).
>
> Disclaimer 2: The situation is different on Android where FFmpeg supports
> libstagefright to decode H264, but I don't know much about it.
>

Thanks for clarifying!

Cheers

Tom