Storyline is not recognzing the MP4 format

Hi Stacy,

MP4 allows both native audio streams (encoded to a standard defined as part of MPEG-4) and private streams (those not part of the MPEG-4 specs). However, there's very little support among software and hardware vendors reading private streams. As a result, if your MP4 file contains audio in a format other than AAC there's a good chance your player won't be able to read it. - http://www.afterdawn.com/glossary/term.cfm/mp4

Most likely the mp4 file in question contains a non-supported combination of audio and video - What is the source of your mp4 file?

You could try to convert your file to a more compatible MPEG-4 format.

https://cloudconvert.org/ (just select from mp4 to mp4)

Hope this helps,

Rutwin