stitch rawvideo with ffmpeg - Picture size 0x0 is invalid

Question

I'm trying to create a timelapse video from several images that I'm fetching from a website. In order to make this faster, my plan was split the workload between multiple cores, each fetching their respective frames (I'm streaming the images to ffmpeg stdin):

ffmpeg -f image2pipe -vcodec mjpeg -i - -f rawvideo part_N

Then I wanted to stitch the rawvideo parts to an mp4:

ffmpeg -f rawvideo -i part_0 -f rawvideo -i part_1 ... output.mp4

But I'm getting the following error:

Picture size 0x0 is invalid`

Answer 1

rawvideo has no metadata so you have to supply all parameters. Since your input is mjpeg (edit: sequence), just keep it as that.

ffmpeg -f image2pipe -vcodec mjpeg -i - -c copy -f mjpeg part_N

Generate a text file like this

file part_0
file part_1
file part_2
...
file part_N

and then

ffmpeg -f concat -safe 0 -r 30 -i list.txt output.mp4

here -r is the desired framerate. Default is 25.