[FFmpeg-user] Causes of color bars?

Simon Roberts simon at dancingcloudservices.com
Wed Jul 15 17:42:47 EEST 2020

On Wed, Jul 15, 2020 at 1:36 AM Marton Balint <cus at passwd.hu> wrote:
> On Wed, 15 Jul 2020, Moritz Barsnick wrote:
> > On Tue, Jul 14, 2020 at 15:50:55 -0600, Simon Roberts wrote:
> >> On Tue, Jul 14, 2020 at 1:29 AM Carl Zwanzig <cpz at tuunq.com> wrote:
> >>
> >> > Decklink boards are _very_ touchy about formats and parameters. Try setting
> >> > at least the resolution and frame rate on the input and see if that helps.

[snip discussion on possible command line params for setting frame and
pixel formats]

> FFplay does not need -i.
> Also the rest if the options are not needed/used for decklink input
> only -format_code matters. Please check the docs for the decklink options:
> https://www.ffmpeg.org/ffmpeg-all.html#Options-57

Aha, thank you Marton, it wasn't the frame format / -format_code, we'd
established with fair confidence that frame format/rate was defaulting
correctly and the problem was with the pixel format, but the info on
setting that was right after the -format_code documentation you
pointed me to, so you saved the day. I always find I get very confused
when trying to navigate the documentation and was clearly looking in
all the wrong places. (I'm still wondering what -pix_fmt and the
others might be for anyway, since they don't seem to work!?) Much
appreciated Marton.

So, my particular solution was to add

    -raw_format argb

after the -f decklink part of the command line. This works for both
ffplay and ffmpeg (both of which matter to me for separate parts of my

It turns out that the splitter that I had most recently bought
(different from the previous model I'd been using, which doesn't seem
to be available any more) results in a pixel format of "argb" instead
of the expected uyvy422 that had been produced by the camera when not
using this particular splitter.

There was actually a hint that something was going on in that sense
because for a few seconds after plugging into this new splitter, the
camera's menu screen popped up a message to the effect of "you've
plugged into a 4K capable TV blah blah". It doesn't do that when
connected to the monitor or the older splitters. So I guess it took
this as an invitation to change modes.

Many thanks again for all the help

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