[FFmpeg-user] RES: A question on the Quadro P6000 and maximum simultaneous NVENC encodes in FFmpeg

Fri Aug 24 01:26:26 EEST 2018

For full GPU transcoding, shouldn't -hwaccel be nvdec?

FFmpeg's documentation on this is missing, but for NVENC, the decoder
should be set to nvdec.

On Fri, 24 Aug 2018 at 01:24, Yang Zhang <yzfedora at gmail.com> wrote:

> If you didn't specify -hwaccel option, then the full gpu transcoding
> is disabled. for example:
>
> 1. full gpu transcoding.
> $ ffmpeg -hwaccel cuvid -c:v h264_cuvid -i test.ts -c:v h264_nvenc ...
>
> 2. gpu transcoding via memory copy.
> $ ffmpeg -c:v h264_cuvid -i test.ts -c:v h264_nvenc ...
>
> 3. cpu decoding and gpu encoding.
> $ ffmpeg -i test.ts -c:v h264_nvenc ...
>
>
>
> On 8/24/18, Dennis Mungai <dmngaie at gmail.com> wrote:
> > Is it possible to disable hwaccel decode explicitly in an FFmpeg
> instance?
> >
> > Say, -hwaccel none such that no hardware-accelerated decoder instance is
> > initialized on launch?
> >
> >
> >
> > On Fri, 24 Aug 2018 at 01:14, Yang Zhang <yzfedora at gmail.com> wrote:
> >
> >> Yes, 25 hd1080p channels use -hwaccel cuvid options to do full hardware
> >> acceleration transcoding. other channels use the GPU encoding only. this
> >> should can let you transcoding more channels. and fix the stutter
> problem.
> >>
> >> You can use "nvidia-smi dmon" to check the usage of NVDEC/ENC chips.
> >>
> >> On Fri, Aug 24, 2018 at 6:02 AM Dennis Mungai <dmngaie at gmail.com>
> wrote:
> >>
> >> > So, to clarify:
> >> >
> >> > If you were to disable hwaccel decode (and rely solely on
> software-based
> >> > decoding) BUT utilize NVENC on a system with a beefy processor and
> >> adequate
> >> > RAM, you should be able to eliminate the bottleneck, correct?
> >> >
> >> > Because what you're implying (by the bottleneck at decode side) would
> be
> >> a
> >> > limitation in how FFmpeg handles filter performance (hwupload, to be
> >> > exact), an issue that can be circumvented by eliminating hwaccel in
> >> decode.
> >> >
> >> >
> >> >
> >> > On Fri, 24 Aug 2018 at 00:57, Yang Zhang <yzfedora at gmail.com> wrote:
> >> >
> >> > > The problem is even you using the Tesla P100, and you can see it
> has 3
> >> > > NVENC chips inside it. but it has only 1 NVDEC chip, this is very
> very
> >> > > important. the bottleneck is at decoding side. this is why you got
> >> > freezing
> >> > > or stutter problem. basically, perhaps you can use Tesla P100
> encoding
> >> 75
> >> > > hd1080p channels, but you can not decoding more than 25 hd1080p
> >> channels
> >> > on
> >> > > it.
> >> > >
> >> > > On Fri, Aug 24, 2018 at 5:51 AM Dennis Mungai <dmngaie at gmail.com>
> >> wrote:
> >> > >
> >> > > > No.
> >> > > >
> >> > > > This is as tested on the Tesla P100.
> >> > > >
> >> > > > On Fri, 24 Aug 2018 at 00:26, Pedro Daniel Costa <
> >> > > > portalnet2 at outlook.com.br>
> >> > > > wrote:
> >> > > >
> >> > > > > Ok
> >> > > > >
> >> > > > > But with the TESLA models, did you have any issues over 40
> >> > > > > streams?
> >> > > > >
> >> > > > > I am planning on budge project to run minimum 100channels
> >> > > > >
> >> > > > > -----Mensagem original-----
> >> > > > > De: ffmpeg-user [mailto:ffmpeg-user-bounces at ffmpeg.org] Em
> nome de
> >> > > > Dennis
> >> > > > > Mungai
> >> > > > > Enviada em: quinta-feira, 23 de agosto de 2018 13:54
> >> > > > > Para: FFmpeg user questions
> >> > > > > Assunto: [FFmpeg-user] A question on the Quadro P6000 and
> maximum
> >> > > > > simultaneous NVENC encodes in FFmpeg
> >> > > > >
> >> > > > > Hello there,
> >> > > > >
> >> > > > > For users with this specific card (and FFmpeg installed), kindly
> >> > > clarify
> >> > > > > on the following:
> >> > > > >
> >> > > > > (a). How many simultaneous encoder sessions can you run on this
> >> card?
> >> > > > >
> >> > > > > (b). Have you ran into any issues, such as stuttering and
> dropping
> >> > > > streams
> >> > > > > with multiple concurrent encodes?
> >> > > > >
> >> > > > > I ask because of a recent case where adding more than ~40
> >> concurrent
> >> > > > > encodes would make the output "drop" and stutter massively, as
> if
> >> > > FFmpeg
> >> > > > > itself was hanging, despite the GPU having more than enough VRAM
> >> > > (24GB?)
> >> > > > > and resources (under ~11% utilization according to nvidia-smi),
> >> > > implying
> >> > > > > some sort of artificial limitation in effect despite the GPU
> >> support
> >> > > > matrix
> >> > > > > specifying otherwise:
> >> > > > >
> >> https://developer.nvidia.com/video-encode-decode-gpu-support-matrix
> >> > > > >
> >> > > > > Your feedback on this is appreciated.
> >> > > > > _______________________________________________
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