Currently I am using this command to extract the images:
ffmpeg.exe -i 10fps.h264 -r 10 -f image2 10fps.h264_%03d.jpeg
But how can I improve the JPEG image quality?
Use -qscale:v
Use -qscale:v (or the alias -q:v) as an output option. Effective range for JPEG is 2-31 with 31 being the worst quality. I recommend trying values of 2-5.
To output a series of images:
ffmpeg -i input.mp4 -qscale:v 2 output_%03d.jpg
To output a single image at ~60 seconds duration:
ffmpeg -ss 60 -i input.mp4 -qscale:v 4 -frames:v 1 output.jpg
This will work with any video input. See below if your input is MJPEG.
MJPEG
If you input is MJPEG (Motion JPEG) then the images can be extracted without any quality loss.
The ffmpeg or ffprobe console output can tell you if your input is MJPEG:
$ ffprobe -v error -select_streams v:0 -show_entries stream=codec_name -of default=nw=1 input.avi
codec_name=mjpeg
Then you can extract the frames using the mjpeg2jpeg bitstream filter:
$ ffmpeg -i input.avi -codec:v copy -bsf:v mjpeg2jpeg output_%03d.jpg
Also see
来源：https://stackoverflow.com/questions/10225403/how-can-i-extract-a-good-quality-jpeg-image-from-an-h264-video-file-with-ffmpeg