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

[Alex P]

Hi James,

I get the same issue with this command:

ffmpeg -f dshow -video_size 3840x2160 -framerate 60000/1001 -rtbufsize 2100000000 -pixel_format bgr24 -i video="MZ0380 PCI, Analog 01 Capture" -c:v h264_nvenc -preset lossless -f null -

Is there a way to accelerate the decoding of rawvideo?

ffmpeg -f dshow -video_size 3840x2160 -framerate 60000/1001 -rtbufsize 2100000000 -pixel_format bgr24 -i video="MZ0380 PCI, Analog 01 Capture" -c:v rawvideo -f null -
Gets me nearly 1x performance. 

-----Original Message-----
From: ffmpeg-user [mailto:ffmpeg-user-bounces at ffmpeg.org] On Behalf Of James Girotti
Sent: Monday, February 12, 2018 3:31 PM
To: FFmpeg user questions
Subject: Re: [FFmpeg-user] 4K 60Hz Directshow Video Capture

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.

HTH,
-J
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