I have a pretty complex animation, Just added some .mp4 audio, and it does not play... unless I am patient? I can scrub around the timeline and the audio will play maybe 50 percent of the time-5 seconds into me waiting regardless of where I am in said timeline. Audio levels are visible. Anyone have a fix to this?
MP4 is about the worst format you could possibly choose for production work. It's highly compressed, takes way too many system resources do decode and is generally not recommended.
Convert the audio file to a 16 bit 48 KHZ PCM wave file (minimum standard for video production) and use that instead. If it still doesn't work, make sure that your AE is up to date and make sure that you have not monkeyed with the preferences unless you know what you are doing. If you are still having problems and your system meets the Minimum System Requirements then we need details.