[FFmpeg-user] Anyone having success capturing hours of 4k video, reliably and with low loss, using ffmpeg?

[Jim DeLaHunt]

Hello, folks:

I'm working with a video production company that is thinking about using 
ffmpeg for a field production. They set up a 4k camera on top of a 
building (have electricity, but limited internet), and they need to 
capture 6-12 hours of 4k 29.92fps video from that camera reliably and 
with very low quality loss. We know we can use ffmpeg to excerpt and 
zoom in on parts of the main video afterwards, if the recording system 
doesn't crash in the middle of the shoot, and if the main video retains 
quality.

Vendor A seems to be saying, buy our expensive system, and it will 
capture the video and put it on a file server which your computer can 
access. But my boss is saying, can't ffmpeg just capture and write out 
the video, and save us the expense of Vendor A?

We tried a simple experiment. We set up a 4K camera in the office. A 
straightforward ffmpeg invocation did capture a couple of minutes of 
video. But there were nasty artifacts, such as 25% of the pixels being 
corrupted in the first second or so, and occasional speckles of 
corruption. This tells me that reliable capture by ffmpeg is easier than 
"impossible", but harder than "works without even trying".

Is anyone on this list capturing hours of 4k video, reliably and with 
low quality loss?  Or, has anyone tried it and discovered that it's 
really, really hard to do it well?  Is ffmpeg up to the task of running 
for 12 hours of capturing 4k video without crashing? What bottlenecks or 
weak points in our capture card or computer do we need to watch out for?

I looked through the archives of /ffmpeg-user/. The most relevant thread 
I found was this: "4K 60Hz Directshow Video Capture"[1] (Feb 2018). The 
conclusion I drew from this thread was circumstantial evidence that my 
task might be reasonable for short periods, and no evidence about longer 
periods like 12 hours. a) they are trying to capture 60Hz, and we only 
want 30Hz. b) it really matters that the capture card exports something 
which is accepted by the ffmpeg code you use. c) disk I/O is a primary 
bottleneck, CPU speed is a secondary bottleneck. d) the right GPU card 
can do the encoding, relieving the CPU speed bottleneck.

The drawback of /ffmpeg-user/ is that generally people post here about 
problems, not about successes. If there are people quietly having 
success with ffmpeg for 12 hours continuously or ffmpeg for 4K video at 
29.92 fps, I'd love to hear it.

[1] <https://ffmpeg.org/pipermail/ffmpeg-user/2018-February/038895.html>

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     --Jim DeLaHunt, jdlh at jdlh.com     http://blog.jdlh.com/ (http://jdlh.com/)
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