Disparity between still quality and video quality

[mattjb1222]

Using the following parameters:
video_width 1280
video_height 1600
video_fps 24
video_mp4box_fps 24.000
video_bitrate 6000000 (I've tried increasing this as high as 24000000)
mjpeg_width 800
mjpeg_quality 8 (I've tried increasing this as high as 100)
mjpeg_divider 4

still_width 1280
still_height 1600
still_quality 14

Recorded videos never even hit 5000kb/s (let alone 6000kb/s), and usually around 4900kb/s
Considerable sharpness & detail is lost as a video file as well, in comparison to still quality.
I've attached a still image taken from pikrellcam as well as a snapshot from the raw h264 file (before it is converted with MP4Box), using video_bitrate 24000000 and mjpeg_quality 100.
Any ideas as to where this quality/sharpness loss is coming from?