This might be implementation dependent. MJPEG per se is not bad as you make it out to be.
Example reviews: https://www.youtube.com/watch?v=daS5RHVAl2U and many more. They all boil down to the same thing: excellent device, even with MJPEG. Obviously it's more dependent on what you use as camera, than the encoding method.
I'm talking about webcams, which have more complex use cases than unprocessed game capture. MJPEG is necessary blocky and bad at low values (shadows); if you're going to chat with friends, streaming it directly, it's probably not going to be noticeable. But if you want to look good, any raw noise or any processing will amplify the compression artifacts, especially in the dark tones, and 4:2:0 will wreck the saturated reds against the opposite background.
Take a look at this OBS forums thread I found, which is a pretty good illustration. [1] This is the best key from a cheap MJPEG webcam I've ever seen, usually it's terrible and streamers have to wear hats. The edge quality in the final picture is still bad (especially hair), and that's with unholy amount of polishing the turd he did, sacrificing latency and probably holding his breath (figuratively) to not go outside of his finely tuned setup. Especially the temporal noise reduction. Check this frame out as well [2], and pay attention to his shirt and hand - the edge is terribly pixelated, which he points out as well. And that is probably the best you can do with the crappy compressed source.
This is the reason cameras like Facecam Pro exist at all. Uncompressed YUV with full chroma resolution makes it all far easier.
> Obviously it's more dependent on what you use as camera, than the encoding method.
You can get away with a cheap camera, if you're using it indoors with controlled lighting; you can't get away with bad compression if you want to process it.
>I'm talking about webcams, which have more complex use cases than unprocessed game capture.
I am too. The HDMI capture card makes a webcam out of a DSLR/DSLM. MJPEG is not the main issue when it comes to quality.
This is still implementation dependent. MJPEG can range from 0-100 in terms of JPEG compression. Also the C920 might also use H264 which would be even worse, also same 4:2:0 issue.
Example reviews: https://www.youtube.com/watch?v=daS5RHVAl2U and many more. They all boil down to the same thing: excellent device, even with MJPEG. Obviously it's more dependent on what you use as camera, than the encoding method.