Canon EOS REBEL T6i Instruction Manual page 234

3 Setting the Movie Recording Size
Compression Method

Standard
Compresses multiple frames at a time efficiently for recording.
Light (v)
The movie is recorded at a low bit rate for playback on various
devices, resulting in a smaller file size than with [Standard].
Therefore, you can shoot longer than with [Standard].
If you change the [53: Video system] setting, set the movie recording size
again.
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