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

Alex P alex.p at avenview.com
Tue Feb 13 23:28:32 EET 2018

Thank you for the offer James, but I think I know how to proceed. 

Looking at the pixel formats for various implementations of x264 and x265, I'm not seeing any that support bgr24, which is the only uncompressed format offered by my capture card, out of yuyv422, yuv420p, nv12, bgr0 and bgr24

Does anyone know of a lossless encoder that inputs and outputs bgr24? 

-----Original Message-----
From: ffmpeg-user [mailto:ffmpeg-user-bounces at ffmpeg.org] On Behalf Of James Girotti
Sent: Tuesday, February 13, 2018 1:33 PM
To: FFmpeg user questions
Subject: Re: [FFmpeg-user] 4K 60Hz Directshow Video Capture

On Tue, Feb 13, 2018 at 6:57 AM, Alex P <alex.p at avenview.com> wrote:

> I think I've figured it out. When I use nv12 or yuv420p as the input 
> and output pixel format, I get x1 performance. If I use bgr24/rgb24 as 
> the input and yuv444p as the output, I get around x0.3.

Looks like switching pixel formats highly impacts performance. It would be better for your capture card to output, for example, yuv444p. I can't tell from the specs if it can do that though.

Careful selecting nv12 as format for output, my quick test showed that the final output was yuv420p.

> In your testing James, what was the pixel format?

I was testing yuv420p samples as that is what was available to me at the time. I have made a yuv444p using testsrc. My poor Thuban cannot decode this FFv1 at realtime and raw-video filesize is gigantic. So I made a lossless hevc yuv444p. Surprisingly (or maybe not) hevc_cuvid can't decode it! Again, my poor Thuban cannot decode real-time, but there's some hope:

FFmpeg encoding speed was about 35-40 fps and hw-encoder utilization topped out at 40%. So there's still a lot of headroom in the hw-encoder. Rough theoretical calculation: I could get 100fps hw-encoding which is ~1.7X

I got about the same speed for h264_nvenc lossless. I got similar results using a 3 second raw yuv444p video input file.

If there are other pix_fmts you would like me to test, let me know. I'll do my best to try.
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