[FFmpeg-user] Low GPU utilization

[Moritz Barsnick]

On Thu, Jan 24, 2019 at 00:07:36 +0330, Mahmood Naderan wrote:
> ./ffmpeg -hwaccel nvdec -i ../4k_normal.mp4 -preset medium -movflags
> +faststart -c:a aac ../4k_normal_conv.mp4
> 
> utilizes the GPU for about 20% according to nvidia-smi. That is pretty low
> while 500MB out of 4GB of device memory is occupied.

You're only using the GPU for decoding. (The "dec" in "nvdec" hints at
this.) The GPU probably idling, while the CPU encoding is the bottleneck.

> Is that normal? Or there are some options missing here?
> ffmpeg has a lot of options and I am confused about how to combine them. If
> somebody can help, I will appreciate it.

Check here for the proper syntax:
https://trac.ffmpeg.org/wiki/HWAccelIntro#NVENCNVDEC

Moritz