Changing these three settings seems to have cleared up the original recording with the stuttering.
Was this to be expected?
Where do I find out the details of the changes you suggested above and an explanation of why these should be the settings I use?
Many thanks, Dave
Basically, if you don't have DXVA selected, the video decoder filter will decode the video stream using the CPU only (and your CPU isn't very powerful, so it can't keep up). DXVA uses the hardware video decoder in the video card (GPU).
Unless you have a good reason to need 'CPU only' decoding (and you fully understand the implications), always select "DXVA2 (native)" in LAV Video Decoder settings.
The reason mm suggests unticking the HEVC and UHD(4k) boxes is because your AMD video card hardware decoder probably can't handle those formats (it's too old).
(DXVA = Direct X Video Acceleration)