What's the diff between 17mbps and 24mbps? at DVinfo.net

Jeff Harper · November 2nd, 2011, 12:41 PM

I've shot in both modes, but haven't yet been able to take the time to analyze the differences. I've got another wedding Friday, and am thinking about going back to 17mbps for the sake of file space.

What kind of differences, practically, are you seeing with the higher bit rate? I know more information is technically going to be better, but is it significant?

Bruce Watson · November 2nd, 2011, 01:28 PM

The higher bit rate generally will show up as smoother motion.

This is especially true for higher contrast motion. For example, if a black clad ninja is moving rapidly toward a target in a scene with a light background, you might see some artifacting (mostly macro-blocking) along his black sleeves and pants legs. A higher bit rate will decrease the amount of the macro-blocking, and depending on the algorithm used, might decrease the size of the blocks themselves. So.... smoother motion.

If what you are shooting is mostly static (like a sit-down interview), you won't likely see any improvement using higher bit rates. AVCHD takes advantage of this by lowering the bit rate automatically for you. So even if you set a max bit rate of 24mpbs, you'll get considerably lower actual bit rate.

Of course, if you are hand holding the camera, or using a lot of pans, tilts, and slider, you are moving everything in the image and therefore will have a considerably higher average bit rate.

Jeff Harper · November 2nd, 2011, 01:35 PM

Bruce, thanks for the explanation. You seem to have said it all. I do recall reading higher bit rates do indeed smooth things out the way you describe, and it makes perfect sense.

Steve Nunez · November 17th, 2011, 04:32 PM

Depending on how the bit rate is allocated- some improvement might be seen with regards to tonal ranges or dynamic range captures with higher bitrates..............hacked GH2's can precisely do this and the larger bitrates display greater dynamic range..........so it might be possible to get increased DR with higher bitrates depending on set parameters.

Buba Kastorski · November 18th, 2011, 09:04 AM

I don't think you can save a lot of space going 17 over 24Mbs, but you might get a slight detail loss in the shadows;
and don't forget stream is peaking at 24 and 17 Mbs, it is 21 and 15Mbs sustained,

November 2nd, 2011, 12:41 PM	#1
Jeff Harper Inner Circle Join Date: Jun 2005 Location: Cincinnati, OH Posts: 8,425	What's the diff between 17mbps and 24mbps? I've shot in both modes, but haven't yet been able to take the time to analyze the differences. I've got another wedding Friday, and am thinking about going back to 17mbps for the sake of file space. What kind of differences, practically, are you seeing with the higher bit rate? I know more information is technically going to be better, but is it significant? __________________ "The horror of what I saw on the timeline cannot be described."

November 2nd, 2011, 01:28 PM	#2
Bruce Watson Major Player Join Date: Mar 2010 Location: Raleigh, NC, USA Posts: 710	Re: What's the diff between 17mbps and 24mbps? The higher bit rate generally will show up as smoother motion. This is especially true for higher contrast motion. For example, if a black clad ninja is moving rapidly toward a target in a scene with a light background, you might see some artifacting (mostly macro-blocking) along his black sleeves and pants legs. A higher bit rate will decrease the amount of the macro-blocking, and depending on the algorithm used, might decrease the size of the blocks themselves. So.... smoother motion. If what you are shooting is mostly static (like a sit-down interview), you won't likely see any improvement using higher bit rates. AVCHD takes advantage of this by lowering the bit rate automatically for you. So even if you set a max bit rate of 24mpbs, you'll get considerably lower actual bit rate. Of course, if you are hand holding the camera, or using a lot of pans, tilts, and slider, you are moving everything in the image and therefore will have a considerably higher average bit rate.

November 2nd, 2011, 01:35 PM	#3
Jeff Harper Inner Circle Join Date: Jun 2005 Location: Cincinnati, OH Posts: 8,425	Re: What's the diff between 17mbps and 24mbps? Bruce, thanks for the explanation. You seem to have said it all. I do recall reading higher bit rates do indeed smooth things out the way you describe, and it makes perfect sense. __________________ "The horror of what I saw on the timeline cannot be described."

November 17th, 2011, 04:32 PM	#4
Steve Nunez Trustee Join Date: Jan 2002 Location: Pembroke Pines, Florida Posts: 1,418	Re: What's the diff between 17mbps and 24mbps? Depending on how the bit rate is allocated- some improvement might be seen with regards to tonal ranges or dynamic range captures with higher bitrates..............hacked GH2's can precisely do this and the larger bitrates display greater dynamic range..........so it might be possible to get increased DR with higher bitrates depending on set parameters. __________________ Steve Nunez-New York City www.stevenunez.com

November 18th, 2011, 09:04 AM	#5
Buba Kastorski Trustee Join Date: Jun 2007 Location: Toronto Posts: 1,414	Re: What's the diff between 17mbps and 24mbps? I don't think you can save a lot of space going 17 over 24Mbs, but you might get a slight detail loss in the shadows; and don't forget stream is peaking at 24 and 17 Mbs, it is 21 and 15Mbs sustained, __________________ I love this place!