Comment by dekhn

I've gotten pretty good at various bits of ffmpeg over time. Its CLI has a certain logic to it... it's order dependent (not all unix CLIs are).

Lately, I've been playing around with more esoteric functionality. For example, storing raw video straight off a video camera on a fairly slow machine. I built a microscope and it reads frames off the camera at 120FPS in raw video format (YUYV 1280x720) which is voluminous if you save it directly to disk (gigs per minute). Disks are cheap but that seemed wasteful, so I was curious about various close-to-lossless techniques to store the exact images, but compressed quickly. I've noticed that RGB24 conversion in ffmpeg is extremely slow, so instead after playing around with the command line I ended up with:

  ffmpeg -f rawvideo -pix_fmt yuyv422 -s 1280x720 -i test.raw  -vcodec libx264 -pix_fmt yuv420p  movie.mp4 -crf 13 -y

This reads in raw video- because raw video doesn't have a container, it lacks metadata like "pixel format" and "image size", so I have to provide those. It's order dependent- everything before "-i test.raw" is for decoding the input, and everythign after is for writing the output. I do one tiny pixel format conversion (that ffmpeg can do really fast) and then write the data out in a very, very close to lossless format with a container (I've found .mkv to be the best container in most cases).

Because I hate command lines, I ended up using ffmpeg-python which composes the command line from this:

  self.process = (
            ffmpeg.
            input(
                "pipe:",
                format="rawvideo",
                pix_fmt="yuyv422",
                s="{}x{}".format(1280, 720),
                threads=8
            )
            .output(
                fname, pix_fmt="yuv422p", vcodec="libx264", crf=13 
            )  
            .overwrite_output()
            .global_args("-threads", "8")
            .run_async(pipe_stdin=True)
            )

and then I literally write() my frames into the stdin of that process. I had to limit the number of threads because the machine has 12 cores and uses at least 2 at all times to run the microscope.

I'm still looking for better/faster lossless YUV encoding.