All sorted.
I downloaded the free version of Any Video Converter and used the settings from here: Video Settings
Playback is now smooth as silk. For good measure I also reformatted the SD Card at 32k.
I also found a useful tip. If you then chuck your newly converted videos in Sansa Media Converter, then hit convert.
If you quickly go to ‘%userprofile%\Documents\Sansa Media Converter\Thumbnail’ you can copy the random Thumbnail to another location.
Cancel the conversion and you then have the Thumbnail for the player.
Just drop it in with the video in the same folder on the player. NiCE.
Am I right in thinking that you can also just rename a .jpg to .thm but with the suffix “VideoName_Large.thm”
Cheers,