Try AVStoDVD. You can output an .iso image or a compliant VIDEO_TS folder https://sites.google.com/site/avstodvdmain/
I installed the program but when I try to open it it says "Windows Common Controls 6.0 ActiveX Library (mscomctl.ocx) is not present or not correctly registered."
See if this post helps - it's by the program author. https://forum.videohelp.com/threads/386443-mscomctl-ocx-error-AVSTODVD#post2507380
Why do you need to convert an MP4 to an ISO? The only point of converting a video to an ISO is to facilitate burning to a disc in a playable format. You don't need to convert an MP4 to an ISO because you can burn it as a data file. Now if you want to convert the file to a disc playable format then we're having a different conversation. So post back and tell us why you want to convert an MP4 to an ISO, and we might be able to send you off on a better direction.
What is the quality of your MP4 files? If they're in high def then you will want to transcode/convert them to a playable BD structure which if small enough can still be burned to a DVD. If it's in a lower def format then you will want to transcode to standard DVD compliant MPEG2 format. There really isn't a lot of good software for the purpose and a lot of it is getting a little long of tooth. Years ago I purchased a copy of VSO's ConvertXto DVD (I was given a really good discount), and I really haven't found much better for the purpose since. For ConvertX you go here! http://www.vso-software.fr/products/convert_x_to_dvd/ If you would like to learn more about everything video, then go here. https://forum.doom9.org/
The MP4's are HD. Thank you for the ConvertXtoDVD information. Next time I convert an MP4 I'll try the trial version.
A lot of Blu-Ray players will play high def MP4s, but remember MP4 is a container and the playback codec can vary depending on the application used to create the original. On a computer this is never an issue since there are codec packs that can be easily downloaded and installed that will cover most situations. On a standalone Blu-Ray player you might have to run it through another application to make it compliant with it. There are codec packs you can download that cover those most commonly used codecs such as K-lite. When you have an intermittent sync problem that usually suggests that the file multiplexing (muxing) was less than perfect. http://www.free-codecs.com/download/k_lite_codec_pack.htm
