Sony has released an update to firmware version 2.00 for the DSC-RX10 camera, giving the camera a new video format. With this release, as seen in the screenshot below, the File Format item on screen 2 of the Shooting menu has a new entry, XAVC S, at the top, in addition to the existing AVCHD and MP4 formats.
The XAVC S format is a consumer version of the XAVC format, which is used for recording 4K video. The 4K standard has a higher resolution than normal HD (high-definition) video, having roughly 4,000 pixels in each horizontal line, instead of the 1,920 pixels in HD video.
The RX10 does not shoot 4K video with the new format, but the XAVC S format does provide a higher bit-rate than the other formats, of 50 megabits per second. In addition, if you select XAVC S for File Format, the Record Setting option, just below File Format on the menu screen, offers choices of 60p, 30p, 24p, and 120p, meaning the camera can shoot progressive video with 24, 30, 60, or 120 full frames per second, as shown on the next screenshot. (These choices are different with cameras sold in countries that use the PAL/50i video standard, which have options of 50p, 100p, and 25p.)
With the 60p or 120p setting, you can record at the fast frame rate and then slow the footage down in your video editing software to produce high-quality slow-motion footage.
So, if high-quality video is important to you, this firmware update is well worth getting.
One important note: If you want to use the XAVC S format for video, you have to use an SDXC card with a speed of at least class 10 and a capacity of at least 64 gigabytes. This is not just a strong recommendation; if you use a card that does not meet those specifications, the camera will display an error message and will not record video using that format.
There is a good discussion of the update along with links to various sites for obtaining the update at the dpreview.com website.