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• ffmpeg : nvidia gpu performance sub-optimal

  3 août 2021, par david furst

  the problem seems fairly basic : i'd like to create thumbnails from incoming video in the shortest time possible, and i'm trying to do this by offloading processing to an nvidia gpu.

  


  while i run ffmpeg, i'm monitoring the gpu usage with the nvidia-smi utility. gpu usage never goes above 15% and the amount of time to encode the thumbnails with gpu is only 10% less than the time required without the gpu. these performance levels are very disappointing.

  


  my question : am i going about this the wrong way (and if so, how should i go about it), or is this gpu performance 'normal'/'reasonable' ?

  


  SYSTEM INFORMATION

  


  the machine is a desktop pc running windows 10, 8gb ram, intel i7-7700. the gpu is an nvidia quadro pro 4000 with cuda 11.4 installed. ffmpeg is version N-101372-gb5cb8c8767-g2fc309e699+4 (2021) running under mingw, with --enable-cuda --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-libnpp --enable-nvdec and --enable-nvenc.

  


  a typical ffmpeg command line i've used is :

  


   1 ffmpeg -hide_banner \
 2     -init_hw_device cuda=cuda:0 -filter_hw_device cuda \
 3     -hwaccel_output_format cuda \
 4     -i "$infile" \
 5     -vf "hwupload_cuda,scale_npp=w=200:h=150:format=yuv420p:interp_algo=lanczos,fps=1/1,hwdownload,format=yuv420p" \
 6     -y "$outdir/%08d.png"


  


  i've varied the above by supplementing some cuda-related parameters according to posts i've read here on stackoverflow and on the nvidia transcoding guide, but haven't been able to improve performance. adding any of -hwaccel cuda, -hwaccel cuvid, -hwaccel nvenc at the beginning of line 3 results in the error :
Impossible to convert between the formats supported by the filter 'graph 0 input from stream 0:0' and the filter 'auto_scaler_0'

  


  any pointers appreciated.

  


• how to set nVidia video bitrate in a system service ?

  12 septembre 2021, par qycx

  I use an nvidia card for compression and decompression in a video conferencing software. The program uses ffmpeg. The program is a system service. Need to control the bit rate. But I found that I didn't control it. The setting code rate was 700k, and the actual value was 10M. What went wrong ?

  


  /* put sample parameters */
    pUnit->encV_var.c->bit_rate = bitrate;//400000;
    /* resolution must be a multiple of two */
    pUnit->encV_var.c->width = in_w;//352;
    pUnit->encV_var.c->height = in_h;//288;
    pUnit->encV_var.c->qmin=10;
    pUnit->encV_var.c->qmax=30;
    /* frames per second */
    AVRational t1={1,25};
    t1.den=fps;
    pUnit->encV_var.c->time_base = t1;//(AVRational){1, 25};
    AVRational t2={25,1};
    t2.num=fps;
    pUnit->encV_var.c->framerate = t2;//(AVRational){25, 1};

    /* emit one intra frame every ten frames
     * check frame pict_type before passing frame
     * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
     * then gop_size is ignored and the output of encoder
     * will always be I frame irrespective to gop_size
     */
    pUnit->encV_var.c->gop_size = 256;//10;
    pUnit->encV_var.c->max_b_frames = 0;//1;
    pUnit->encV_var.c->pix_fmt = AV_PIX_FMT_YUV420P;


  


• What's the difference between H265, x265, x264, H264 and which of these uses GPU instead of CPU and how to use H265 GPU NVIDIA acceleration in ffmpeg ?

  30 juillet 2022, par Fab98

  I'm not sure if
x264/5
use CPU and if h264/5 use GPU and also if h265 is basically HEVC_NVENC for NVIDIA GPU acceleration. So, if you could give me more info about these encoding types it would be great. I understood that, summing up a lot, x26* use CPU and are slower but more accurate while h26* are the opposite but h265 is the most recent and optimal trade off.
Furthermore, I was trying to convert a video using GPU acceleration and my question is :

  


  Does the following command tell to the GPU to use h265 to encode a video holding the same audio and at upgrading it at its maximum video quality ? Furthermore, are there other ways to express the same command ?

  


  ffmpeg.exe -hwaccel_output_format cuda -i "input" -c:v hevc_nvenc -preset medium -rc constqp -qp 0 -c:a copy "output"