MP3 IS 25 YEARS OLD!
I understand that you want to select a frame from your mp4 file and turn it into an image and then rename it. I know FFmpeg output is more similar to QuickTime if you set it to png. Also, you can create the still frames in Resolve because there is probably a way to do so. If this method does not work, you can try to convert mp4 video files to screenshots. Several free online applications allow this, and you can also request the script for this action.
Thousands. I had a Zen player with a huge memory before ipods even came out.
Zen ? OH, you're the ONE ! -- I'm a monopolsoft (MS) bigot