ffmpeg generate higher quality images for MJPEG encoding

Question

I have a bunch of mov / H.264 files, that I'd like to encode into mov/MJPEG. However I'm getting very low quality output. Here's what I tried:

ffmpeg -i a.mov -an -crf 11 -preset slower -pix_fmt yuv420p -vcodec mjpeg -f mov -y b.mov

For H.264 encoding the -crf and -preset flags generate higher quality. But that doesn't seem to work for MJPEG.

Solution

Use -q:v to control (M)JPEG quality

The effective range is a linear scale of 2-31, and a lower value will result in a higher quality output.

Examples

Make MJPEG video in MOV container:

ffmpeg -i input.mov -c:v mjpeg -q:v 3 -an output.mov

Output a series of JPG images:

ffmpeg -i input.mov -q:v 2 images_%04d.jpg

Files will be named images_0001.jpg, images_0002.jpg, images_0003.jpg, etc.

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Private options

For H.264 encoding the -crf and -preset flags generate higher quality. But that doesn't seem to work for MJPEG.

The MJPEG encoder does not use -crf and -preset; these are "private" options for some encoders such as libx264, libx265, and libvpx. You can see private options like this: ffmpeg -h encoder=mjpeg.