Why does watching videos cause my Nokia Lumia 520 to lose bytes?

[Windows Central Question]

I have a Nokia Lumia 520 and it seems that when I watch a certain amount of videos my phone loses space.

But I have no clue why, this has happened before, but I hadn't updated it in the past and once I did, my phone had about two-three gigabytes again, I checked if had to update something, but that isn't the case.

All the apps on my phone combined take in about two gigabytes, however I also have
an SD-card of 7 gigabytes that's far from full. In short, why am I rapidly losing bytes from watching videos and can I do something about it, because it'd be rather troublesome if I become unable to watch videos on my phone

PS: I apologize for any errors, English is not my native language.

 

[xandros9]

Are you streaming these videos?

 

[Fatine009]

Only short videos on YouTube, thought sometimes they're up to 10 minutes or so, I only watch long episodes of series on apps I have downloaded especially for this purpose. Though these apps are downloaded using my SD-card, my phone still loses bytes.

 

[worldspy99]

Do you recover the space back once you delete the videos after watching? Also do you get the space back after clearing the temporary files?

 

[Fatine009]

It seems most of my space (4,2 GB to be precise) is taken in by Media and Files, but how do I delete these?

 

[Fatine009]

Also, yes I do get space back after clearing temporary files.