How to create a x264 (mp4) video with the smallest size using ffmpeg that has just 1 image through entire video? I'm creating narrated mp4 (x264+aac) videos for books. Each video has just the book's cover as the background.

I wonder what would be the most effective way to create such videos with ffmpeg?

I've tried using framerate of 1fps and that created small videos, but there were problems seeking in the video, and some video playing libraries for web browsers got confused with such videos.

Do you have any recommendations for creating small mp4 videos with just 1 static frame?
ffmpeg will do it for you - https://stackoverflow.com/questions/5887311/ffmpeg-1-image-1-audio-file-1-video

If you want to provide good seeking ability, you will need to provide key frames at certain intervals in the encoding, which will increase the size of the video. The codec will encode the whole frame at each of the keyframes but greatly compress the intervening frames. By playing around with the value of the key frame interval, you can arrive at a good compromise for your needs.