1.Use the SYSTEM_SW_MS_LINK_CMD_SET_FRAME_RATE to set the correct input and output fps rate required.
This will result in swms dropping input frames at equal interval.
2. When connected to display enable SwMsPrm.processTiedWithDispaly flag to TRUE.
3. WHen Swms input is 30 and connected to display of 60 fps set swmsPrm.enableOutputDup = TRUE.
4. There is nothing much that can be done for 50 fps input 30 fps output apart from setting SYSTEM_SW_MS_LINK_CMD_SET_FRAME_RATE param. There is bound to be noticeable frame repeat since each time delta between frames will not be equal.I suggest you encode at 50 or 25 fps which is reasonable for 50 fps capture.
5. Disable avsync is you have enabled it in swms.