When recording to SD card it cuts out after 20 minutes

It is FAT32 system limitation for the 4GB gets split.  The only solution is to change format from FAT32 to exFAT.
Unfortunately, C875 is old time product. Under PC free mode, C875 only support to SDHC card (notes: only support FAT32), instead of supporting to "microSD card". Micro SD Supported 2 formats: FAT32 format / exFAT format. It necessary to use exFAT format to prevent 4GB split issue.

Due to the specification of FAT32, movies are divided and saved every 4 GB (about 25 minutes).
- Continuous recording is possible when using "exFAT format" microSD card

We have released new product GC513 for PC free mode recording. GC513 can support micro SD card. Then you could format “exFAT” on your micro SD card.