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

[Dragan Randjelovic]

Recommendation:

-several ssd drives in raid 0 configuration ex. Samsung EVO PRO ( allows
for capacity and speed, and longer read/write life-cycle)  Calculate the
space you need based on codec selection or god forbid based on that long 4K
raw video :)
-use thunderbolt port straight from camera or capture trough some interface
like Black Magic 4K studio pro (preferably over sdi interface) and/or BM
intensity (sdi/hdmi -> thunderbolt.->PC)

use either software coming with the capturing board (which will allow you
to test performance metrics of critical components and show if you are
short on something, offer you a few codec for trans-coding on the fly
etc..) or use ffmpeg with manners ( blackmagic is supported with a caveat -
non-free license, in other words you have to compile ffmpeg for yourself)
Try not to record raw but to transcode on the fly or make use of camera's
potentially built in encoder. Now here is a critical part! Do you have a
reference signal? If not camera can become your reference clock. Rethink
and interconnect reference signal between capturing adapter and camera.
Moreover it's up to you to select the codec of choice ex. AVC intra wont
blow up your core i7 4th gen or newer box. As far as refresh rate value
goes, make sure that both camera and capturing adapter support desired one.
Capture long and prosper!

P>S. Oh sorry I just read top of the house part. I guess 100m is enough.
Forget about clock and use SDI over coax.

This looks like off topic isn't it ?

Regards.
Dragan


On Thu, Jun 28, 2018 at 9:58 PM, Jim DeLaHunt <from.ffmpeg-user at jdlh.com>
wrote:

> 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>
>
> --
>     --Jim DeLaHunt, jdlh at jdlh.com     http://blog.jdlh.com/ (
> http://jdlh.com/)
>       multilingual websites consultant
>
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