Canon released a new firmware for the C300:
Firmware Version 188.8.131.52.00 incorporates the following improvements and fixes:
1. Supports exFAT file system of CF cards over 128 GB, which decreases the waiting time required for accessing the card before being able to record footage.
2. Simplifies the process when fine-tuning the preset White Balance values.
Firmware Version 184.108.40.206.00 is only for EOS C300 cameras with the Dual Pixel CMOS AF Feature Upgrade applied. If the EOS C300 camera does not have Dual Pixel CMOS AF Feature Upgrade applied, please download Firmware Version 220.127.116.11.00.
Firmware Version 18.104.22.168.00 is for Cinema EOS C300 cameras running firmware version 22.214.171.124.00. If the camera’s firmware is already version 126.96.36.199.00, it is not necessary to update the firmware. Once the camera is updated to the latest firmware version, it cannot be restored to a previous version.