overcranking bitrates at DVinfo.net
DV Info Net

Go Back   DV Info Net > Panasonic P2HD / AVCCAM / AVCHD / DV Camera Systems > Panasonic AVCCAM Camcorders

Panasonic AVCCAM Camcorders
AVCHD for pro applications: AG-AC160, AC130 and other AVCCAM gear.

Reply
 
Thread Tools Search this Thread
Old January 3rd, 2012, 05:06 AM   #1
Regular Crew
 
Join Date: Jun 2008
Location: Christchurch, New Zealand
Posts: 55
overcranking bitrates

Hi- I'm looking for a camera to do some slow-motion work, and it's exciting to see 50 and 60p everywhere now. I see people shooting everything at 50p, and it seems a lovely option, to be able to use slow-motion at will. But I do wonder: doesn't shooting 50p, say (I'm in PAL territory) mean you are effectively halving the bit-rate of the recording? And if the maximum quality is 24 Mbs and you're shooting twice the frame-rate, does anyone notice any serious lowering of quality?
I've shot 50 fps on a jvc HM100, and it looked very clean, but it's shooting at 35Mbs, and it was 720p so less info. I have also tried the 50 fps option on a jvc HD201 recording 720p hdv at 19 Mbs. It looked fine for tripod shots, slow moves etc, but fast motion tended to break up the detail- and what is an acceptable blur at full-speed doesn't look so good slowed down.
So how does the AVCCAM codec handle halving the bit-rate per frame? At 720 or 1080? I'm thinking of using it for commercials, where the image needs to stay clean. Anyone looked at this with a critical eye?
Rob Stowell is offline   Reply With Quote
Old January 3rd, 2012, 01:21 PM   #2
Major Player
 
Join Date: Mar 2010
Location: Raleigh, NC, USA
Posts: 710
Re: overcranking bitrates

Quote:
Originally Posted by Rob Stowell View Post
... doesn't shooting 50p, say (I'm in PAL territory) mean you are effectively halving the bit-rate of the recording?
Not really. Depends on the hardware and especially the CODEC. A modern long-GOP codec like AVCHD will give you about the same bit rate, and almost no loss in video quality. The reason is that it's mostly recording the difference between the video frames. And with double the frames, you get about half the difference between the frames. So it works out pretty well.

For example, the specs on AVCHD give you a max bit rate of 24Mbps at the highest quality setting (30 fps). With AVCHD 2.0, it's raised to just 28Mbps, but with double the frame rate (60 fps). This is just grabbing numbers from memory -- if I'm off I'm sure someone will correct me.
Bruce Watson is offline   Reply With Quote
Old January 6th, 2012, 03:45 PM   #3
Major Player
 
Join Date: Feb 2010
Location: London
Posts: 302
Re: overcranking bitrates

Hi

The above is exactly right, and on Panasonic camcorders at least, the 28Mbit/sec bitrate can easily peak greater than 30, I've seen peaks of 35 before now giving good head room for difficult to encode scenes.

Also progressive footage is easier to compress than interlaced as these modern codecs really want to work with progressive footage, and as you go up the quality scale (Levels) of something like AVC/H264, it doesn't support interlaced footage at all.

Also as pointed out, the more frames per second gives the encoder greater opportunity to find similarities between groups of frames and track motion from one frame to another.

Regards

Phil
Phil Lee is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

B&H Photo Video
(866) 521-7381
New York, NY USA

Scan Computers Int. Ltd.
+44 0871-472-4747
Bolton, Lancashire UK


DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > Panasonic P2HD / AVCCAM / AVCHD / DV Camera Systems > Panasonic AVCCAM Camcorders

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



All times are GMT -6. The time now is 12:12 AM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2024 The Digital Video Information Network