[FFmpeg-user] ffmpeg chromakey with v4l2 loopback device

[Steven Varga]

Hello,

when running the following ffmpeg chain I can't set the output psudo device
(/dev/video1) format. What am I doing wrong?
best
steven

error message:
[v4l2 @ 0x55e5418ddee0] Unknown V4L2 pixel format equivalent for yuva420p
Could not write header for output file #0 (incorrect codec parameters ?):
Invalid argument
Error initializing output stream 0:0 --

command line:
ffmpeg -i Pictures/city.png -i /dev/video0 -filter_complex
'[1:v]colorkey=blue:.2:0.0[ckout];[0:v][ckout]overlay[out]' -map '[out]' -f
v4l2 /dev/video1

steven at honshu:~/src/v4l2loopback$ modinfo v4l2loopback
filename:       /lib/modules/4.15.0-20-generic/extra/v4l2loopback.ko
license:        GPL
author:         Vasily Levin, IOhannes m zmoelnig <zmoelnig at iem.at>,Stefan
Diewald,Anton Novikovet al.
description:    V4L2 loopback video device
srcversion:     F970FD08DB80D838C18FFD7
depends:        videodev
retpoline:      Y
name:           v4l2loopback
vermagic:       4.15.0-20-generic SMP mod_unload
parm:           debug:debugging level (higher values == more verbose) (int)
parm:           max_buffers:how many buffers should be allocated (int)
parm:           max_openers:how many users can open loopback device (int)
parm:           devices:how many devices should be created (int)
parm:           video_nr:video device numbers (-1=auto, 0=/dev/video0,
etc.) (array of int)
parm:           card_label:card labels for every device (array of charp)
parm:           exclusive_caps:whether to announce OUTPUT/CAPTURE
capabilities exclusively or not (array of bool)
parm:           max_width:maximum frame width (int)
module installed from github source with last commit:
commit f998233aafa92a268a91929705e1b453b98f1b9d (HEAD -> master,
origin/master, origin/HEAD)
Author: IOhannes m zmölnig <zmoelnig at umlautS.umlaeute.mur.at>
Date:   Thu Nov 15 21:52:38 2018 +0100

Distributor ID: LinuxMint
Description: Linux Mint 19.1 Tessa
Release: 19.1 Codename: tessa