[FFmpeg-user] 4K 60Hz Directshow Video Capture

James Girotti james.girotti at gmail.com
Mon Feb 12 22:31:16 EET 2018

Hi Alex,

I looked at your attached log. It appears to me that using libx265, your
computer cannot encode fast enough. It appears your computer is encoding
about 10.5 fps, but your input is about 60fps. So a lot of frames get
buffered every second while they're waiting to be encoded. This leads to
the full rtbuffer and then dropped frames. You could try increasing your
rtbufsize, but using libx265 your computer will not be able to keep up and
eventually the buffer will fill and frames will be dropped.

> Any help would be appreciated. 1080p capture right to rawvideo is perfect.
> I
> would like to use NVENC in lossless mode if anyone has experience with
> that.

If you look at the fps that you can do at 1080p, it will be much higher and
that's why you don't get buffer over-runs.

I also have a GTX 1050 Ti that I use for encoding. It will do hevc lossless
at about 150fps, input size 3840x2160 at 60hz (all in RAM):

ffmpeg -hwaccel cuvid -c:v hevc_cuvid -i /dev/shm/foo.4k60.hevc.mkv -c:v
hevc_cuvid -preset lossless /dev/shm/test.mkv

Based on my limited test, your GPU should be able to keep up and not drop
frames, YMMV. I'm not sure what impact you will have because your input is
raw-video (positive or negative). You shouldn't include "-hwaccel cuvid" on
your cli, because you won't be doing hw-decoding/transcoding.


More information about the ffmpeg-user mailing list