A user will have to resize this dialog the first time its opened, so it would be good to change it from its current ~380x~280px size to something like 530x400px. It would also be useful to adjust the video control so that it has some spacing on its top and left.
Let's say I believe you, but how do I get to this "Media player dialog"?
You can find it in Impress through Tools > Media Player or in all apps by opening the gallery and clicking on the sounds gallery and double clicking on a sound.
it's (480, 360) by default, quite similar to the numbers you suggested.
I guess we can close this one too...