When I render a scene and then play it back it lags in the video player, sometimes if I play it over a few times the lag goes away but how do I stop this happening? I looked it up and people with what sounds like the same problem are being told their scene is too uncompressed, is that right? How much compression is the right amount?
In Render Settings > Save > Format: QuickTime Movie > Options I have the slider for quality in the compression section set to best, should I turn that down? Why even include the option if it lags during playback?
If the video is uncompressed (.avi or .mov), then it will most likely lag when you play it back on your computer for preview unless you have a really fast computer. If that's your final render, you might want to consider compressing it, especially if you're going to upload it or transfer. If you're still going to to further edits, uncompressed footage is fine because you will get the best quality possible! Just make sure that your final render is compressed so you can actually watch it.
Personally, I use the Quicktime format with H.264 compression, then check the limit box. I usually limit it to 1728 KB/sec because it matches my original footage's bitrate (13.5 Mb/sec, it's the same)