I am using ffmpeg to add an image as a first frame. This one works but the issue is that the colors are being faded. My attempt was to check the color encoding of the input video and apply it to the output video but still the issue is there.

What I found out is that this issue does not happen when I use a frame from the video, so it somehow related to using an image.

This is my command to add an image as thumbnail:

ffmpeg -loop 1 -framerate 30 -t 0.5 -i thumbnail.png -f lavfi -t 0.5 -i aevalsrc=0 -i input_video.mp4 -filter_complex "[0:v][1:a][2:v][2:a] concat=n=2:v=1:a=1" -shortest -color_primaries bt2020 -color_trc bt709 -colorspace bt709 output_test1.mp4

Screenshot of the original and the output video. Left is the original with brighter colors compared to the output on the right.