Issues exporting video made from jpegs

I have created a video using 50 JPEG files - all the same resolution etc, and added on an audio from another video file. I am having issues when trying to export it. When I export it as a mp4, the video flickers constantly and I can’t see the pictures. When I try and export it as a H264 (as suggested by other threads), it keeps failing.
How can I export it without the flicker?
Thanks for your help!

You’ve told us nothing about your export settings other than mp4.
50 JPEG images would be a touch over 2 seconds long at 24fps.

Sorry about that. I have used the 50 images over a video recorded on an iphone, which lasts an hour. The picture dimensions are 1274x955, and each picture is shown to match the audio. I exported it using the default mp4 export settings.
Let me know if you need any other information!

Before exporting, go to “Codec” section and change quality to 100% (deflaut is 60%). This worked for me, let me know if it helps!