To get the best quality out of your video captures, it’s best to capture losslessly and encode the content post-capture rather than trying to do it in real-time via software encoding or using hardware encoders. Unfortunately normal raw lossless capturing requires very fast storage and a pretty hefty amount of disk space. SSD drives can cope, but depending on the length of your captures you may well need over 2TB of space, which is currently quite expensive in SSD form. An alternative is to use RAID0 arrays or similar. If your storage cannot keep up with the required write speeds you will end up with dropped frames.
A great solution is using the x264vfw codec in lossless mode. You will still have large file sizes (expect past 1GB or more for every minute), however the sizes are much smaller than normal raw lossless capture. This also means the write speeds required for capturing without losing any frames are lower. The highest I’ve seen x264vfw jump in lossless mode is ~60MB/s when a ton of action is going on, otherwise in my captures I’ve seen speeds generally hang around 20MB/s. A standard HDD can cope with this without issue, just make sure the drive isn’t being used by anything else.
For more info on x264vfw, other lossless codecs, and capturing in general – Check out “TheThrillness Blog”.