Video Playback not working Sony MP4 Player

[Aleatoire]

Hi, I've had a Sony NWZ-E438F 8GB MP4 player for a while now and I've only just got round to trying to find out why some MPEG-4 movies won't play on it.

I've got some movies on my PC that I wan't to have on my MP4 but after transferring them onto it, I get a message telling me that I can't play them.
They are in MPEG-4 format. This only happens with some videos, not all of them.

Any ideas why this is happening?

 

[JAYDEEJOHN]

You cant link to illegal activities here

 

[Aleatoire]

Wait, how is this illegal?
If it's illegal to put movies on my MP4 player then why does it play MPEG-4 files?
And I haven't linked to anything, I only asked a question.

EDIT: Unless you mean it's illegal to put actual "movies" on my MP4 because thats not what I meant (I should have phrased my question slightly better). I was talking about drum covers of songs by a guy called Cobus Potgieter which are completely copyright free. In fact you can download them from his website if you don't believe me.