HMC-150 What's with my DATA RATE??!

T

The Irish TRex

Well-known member
Hi y'all!

What's with my data rates?! ...Just purchased two HMC150s for my Wedding shoots. Been shooting with DVX100B for YEARS and it was time. I immediately starting shooting Weddings with them the day after I got them using the Panasonic Class 10 sdhc cards. Now I'm starting my first edit using FCP. As a test I've uploaded the following 5 clips via log & transfer which thus made them Apple ProRes 422 files. Each clip is exactly 15 seconds. When I click on properties for each clip in FCP here's what it shows:


  • CLIP #1: 15secs - 1080p24 - 210.0mb - 1920x1080 - Square Pixels - 23.98fps - DATA RATE: 13.9mb/s
  • CLIP #2: 15secs - 1080p24 - 211.1mb - 1920x1080 - Square Pixels - 23.98fps - DATA RATE: 14.0mb/s (NOTE: I chose 2 separate 1080p24 clips for fun just to see if theres a data rate or file size difference)
  • CLIP #3: 15secs - 720p24 - 106.9mb - 1280x720 - Square Pixels - 23.98fps - DATA RATE: 7.1mb/s
  • CLIP #4: 15secs - 720p60 - 267.5mb - 1280x720 - Square Pixels - 59.94fps - DATA RATE: 17.8mb/s
  • CLIP #5: 15secs - 720p60 - 257.0mb - 1280x720 - Square Pixels - 59.94fps - DATA RATE: 17.1mb/s (Again...I just did 2 separate 720p60 clips for fun just to see if there's a data rate or file size difference)
BTW, just for fun...I noticed my DVX footage 24p squeezed footage was 2.9mb/s. That has nothing to do with my question though (sorry TMI)...my real point here is the above 5 CLIPS...So...

...What's with the DATA RATE??!! I thought 1080p24 is supposed to be around 21mb/s??? Everything was shot in PH mode (I'm not sure there's even an option to shoot 1080p24 outside of PH mode) so the quality should be optimal. The footage looks okay to my eye but this data rate thing throws me.

Why is the 720p60 a higher data rate than the others? And MOST IMPORTANTLY what's with the 1080p24 having a low data rate (compared to what I've read that it should be around 21mb/s) and whats with the super low 720p24 low data rate. Is all this normal? Please explain for me!

Thank you!!!

I eagerly await your responses.
 
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You are confusing megabits and megabytes. The camera records 21 megabits. When you convert to Prores you are converting to a I frame only video format which can take many megabytes per second. Since it is an I frame format your datarate will vary based on the framerate. 720p 24p will be much smaller then 720p 60p because there are that many less frames to compress with Prores.

Your datarate reading inside of FCP has nothing at all to do with the camera recording format.
 
Ah. Ok. There was very limited movement beyond just people standing and talking. But sounds like I'm reading this the wrong way I guess.

FOLLOW-UP QUESTION: So there is nothing out of the ordinary with what I see in FCP? I'm not shooting incorrectly (as far as trying to achieve the highest quality with regards to 21mb/s)? So that output I'm seeing of 13.9mb/s is megabytes and doesn't necessarily mean that it wasn't actually recorded at 21 megabits/second?

Basically, everything is cool?
 
It's not out of the ordinary at all.

21 mega bits / second (mb/s) is only 2.625 mega bytes / second (MB/s). Importing and transcoding to ProRes 422 means it's now being stored at a higher bit rate than the highest bitrate that the HMC can record at. So, don't worry about it any more because I think you've been confusing mb/s with MB/s. They are not the same thing.
 
some other theoretical reference numbers: (dividing by 8 is fun!)
DVCPRO HD - 100Mbps = 12.5 MBps
1394a port - 400Mbps = 50MBps (though you'll never achieve that speed)
SATA 3Gbps - 3,072Mbps = 384 MBps (Average single Hard drive or SSD can't fill that bus)
http://www.matisse.net/bitcalc/ has been my go to tool for awhile now
 
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