The Canon function mvrSetDefQScale(int16_t *) (2.0.8 0xff990188) sets the quality parameter to the camera’s h.264 encoder. If the CF card is not able to keep up, the camera will display a buffer-level bar on the right side of the LCD and stop recording when it hits full. The parameter does not have any effect unless fixed bit rate encoding is selected via mvrFixQScale(int16_t *) (2.0.8 0xff9905d4).
The default q-scale is -8 in VBR mode and has a nominal 42 Mbps with the 2.0.8 firmware. The 24p tests were done with the camera on a tripod writing to a Lexar 400x UDMA 16 GB card with all Magic Lantern tasks disabled (no zebras, cropmarks, etc). qscales less than -12 occasionally stopped recording.
|+8||30p||7 MBps||Very low quality|
|-14||24p||66 MBps||Best, sustainable in 24p mode?|
|-15||24p||68 MBps||2 buffer bars|
|-16||24p||76 MBps||Only a few seconds|
- 24p seems to have less issues than 30p
- Locked-off shots seem less likely to trigger buffer overflows; amount of motion?
- Auto-exposure changes seems to lead to immediate overflows: shoot manual exposure mode
- -14 seems to be the best that can be sustained with the card with all other ML tasks running.
- Download it from this ml-devel post