Some more information about this warning: It only occurs when one image in the input list differs in size from the previous image. If the dimensions are significantly different, visible distortion will occur. Also, in contrast to my previous post, it appears that PNG images are bypassed with a warning. JPG images do work; I don't know what other formats might be possible. _______________________________________________ 2017-05-01 09:25:52 UTC <ceffmpeg@gmail.com> [swscaler @ 0x9d13040] deprecated pixel format used,make sure you did set range correctly You cannot fix this warning and it should not trouble you. Carl Eugen _______________________________________________ ffmpeg -f concat -i input.txt -vsync vfr -pix_fmt yuv420p test.mp4 This did work. "test.mp4" is a video with all the images, each displaying for about 5 seconds. But ffmpeg gave the following complaint for each image: [swscaler @ 0x9d13040] deprecated pixel format used, make sure you did set range correctly