MPEG IMX is a 2001 development of the Digital Betacam format. It uses the MPEG compression system, but at a higher bitrate than Betacam SX. The IMX format allows for a CCIR 601 compliant video signal, with eight channels of audio and timecode track. It lacks an analog audio (cue) track as the Digital Betacam, but will read it as channel 7 if used for playback.
Compression is applied in three different formats: 30 (6:1 compression), 40 (4:1 compression) or 50 Mbit/s (3.3:1 compression) which allows different quality/storage efficiency ratios. Video is recorded as MPEG-2 I frames only.
Well, IMX30 has a bitrate of 30 mb/s (megabits), so a 10 sec clip should be 37.5 mB (megabytes) of video. Don't remember the audio format for IMX, but I'll guess 16 bit 48k, which in 8 channels for 10 secs should be 7.68 mB. Then add some metadata on top of that, and you should have an approximate size.