Hi

I wonder if someone can help out. I have the newest version (I think, there was an update a while ago) of Sony Vegas Pro 20. (I'm a Windows-user)

The 1st problem is this:

I'm trying to edit a video which contains multiple short videos taken with phone or a GoPro camera, and additional audio/music. The GoPro can film 4K videos and the quality of the phone is HD. While editing, the preview screen goes black very often, which obviously makes it difficult to edit. I've tried to reduce the quality of the preview screen, but it does not help. What should I do with this?

The 2nd problem:

When rendered, the finished video is also lagging and clips seem to be "missing"; it shows black screen. Sometimes the audio is still playing, so I suppose it has not actually lost the clips but can't function properly. Is the file size too large? I've tried two different mediaplayers to watch the rendered video, and they both have this issue. I've tried to render the video as Video for Windows (HD 1080-60i YUV) and AVC/AAC/mp4 (Blue-ray 1440x1080-24p, 25 Mbps video stream), but there is no difference. I've tried MPEG-file (M2T-file, HDV 720-30p) but that as well has the same issue. Also, regarding MPEG I'm worried it won't play in all devices we would need it to. The file/format should be something that will be compatible/will play on mainly computers/laptops and PlayStation.

I've edited videos many years, but I'm a beginner with these technical things (such as file sizes and stuff) and terms :D In addition, english is not my native language. So if you know how to fix this, please try to explain with simple terms, thank you! I used to have Vegas Pro 10 many years ago, and I remember having this same problem back then but could not fix it (different computers). So now that I started editing again, I was concerned that this might still be an issue, but I bought the Vegas Pro 20 anyway. And, well. I'm dissapointed tbh. But, maybe there's a fix for this? I hope.

Sorry for possibly dum questions :D and thank you in advance!