Sony DSC-W830 - Manual (Page 199)

The recordable time of movies varies because the camera is equipped with VBR (Variable Bit Rate), which
automatically adjusts image quality depending on the shooting scene.
When you record a fast-moving subject, the image is clearer but the recordable time is shorter because more memory
is required for recording.
Recordable time also varies depending on shooting conditions, subject or image quality/size settings.
You cannot record movies to internal memory when the movie image size is [1280x720(Fine)] or
[1280x720(Standard)].
Notes on use
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