Canon EOS R10 User Manual page 418

If you use a card with a slow writing speed, an indicator may appear on the right
of the screen during movie recording. The indicator shows how much data has
not yet been written to the card (remaining capacity of the internal buffer
memory), and it increases more quickly the slower the card is. If the indicator (1)
becomes full, movie recording will stop automatically.
If the card has a fast writing speed, the indicator will not appear or the level (if
displayed) will not increase much. First, record a few test movies to see if the card
can write fast enough.
If the indicator shows that the card is full, and movie recording stops automatically,
the sound near the end of the movie may not be recorded properly.
If the card's writing speed is slow (due to fragmentation) and the indicator appears,
formatting the card may make the writing speed faster.
Note
Notes for movie recording
Each time you record a movie, a new movie file is created on the card.
Field of view (coverage) is approx. 100%.
Focusing is also possible by pressing the < > button.
To enable starting/stopping movie recording by pressing the shutter button
completely, set [Fully-press] for [ : Shutter btn function for movies] to [Start/
stop mov rec] ( ).
Most external microphones equipped with a 3.5 mm mini-plug can be used.
Any connected external microphone is used instead of the built-in microphone.
Focus preset during movie recording is available when using (super) telephoto
lenses equipped with this function released in and after the second half of 2011.
YCbCr 4:2:0 (8-bit) color sampling and the BT.709 color space are used for 4K and
Full HD movies.
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