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AVCHD Format Discussion
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Old July 25th, 2006, 04:42 AM   #1
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AVCHD 24mb/s or 18mb/s plus 6mb/s audio?

I spotted this the last week or so, in the charts

http://panasonic.co.jp/corp/news/off...n060713-3.html

It says that system is Mpeg2 transport system, and that the system bit rate is "upto 24Mbs". Does this include the audio streams?

It says that the linear PCM 2 channel audio requirement is 1.5Mb/s, and that it can do 7.1. 7.1 audio would be then 6Mb/s, and taking that off of 24Mb/s we get the original 18mb/s of the original AVC announcement. But it gets worse, consider that the announced Samsung h264 720p camera gets around 16-17Mb/s, but that is at 50/60fps, not 25/30fps.

It could be that audio is in addition, or that the AVCHD video side might still be the original 18mb/s format, and less than what we were expecting.
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Old July 25th, 2006, 10:32 AM   #2
 
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It could be that audio is in addition, or that the AVCHD video side might still be the original 18mb/s format, and less than what we were expecting.

This would be correct. Now, that isn't to say that Panasonic might not do something outside the spec. JVC and Canon did just that with the 24p modes of their HDV offerings, and eventually those modes became part of the HDV spec. Panasonic, not being a member of the HDV consortium somewhat could use an argument to the lower bitrates and price points of HDV and where it's going.
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Old July 25th, 2006, 10:36 AM   #3
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hmm. i can see your concerns, however when u consider that these codecs are cleaner, far more efficient and have been proven to exceed the colour, gradation and noise levels of MPG, everything we know today is insignificant, until we see these codecs in action..

what i mean is that the bitrate may seem low now, but the codec is far more efficient, hence not requireing the large bitrates as fond in DV and HDV.
As an example, ive seen 3mbps DivX/mp4 absolutely poo on MPG2 at 9mbps
And in all honesty, id rather have have uncomrpessed audio as opposed to highly compressed MPG1 audio streams as found in HDV...
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Old July 25th, 2006, 10:41 AM   #4
 
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Quote:
Originally Posted by Peter Jefferson
And in all honesty, id rather have have uncomrpessed audio as opposed to highly compressed MPG1 audio streams as found in HDV...
I'd rather have uncompressed too, but at a 4:1 compression ratio, HDV audio is hardly "highly compressed."
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Old July 25th, 2006, 11:19 AM   #5
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Why would a camera record 7.1 channels of uncompressed audio? As far as I know that goofy mic thing SONY has can only do 5.1 channels. I would think there would be an option for either 2 channel uncompressed or dolby 5.1 with the camera itself. The format itself may support more channels but I doubt the camera will do it.
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Old July 25th, 2006, 12:05 PM   #6
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Quote:
Originally Posted by Peter Jefferson
the bitrate may seem low now, but the codec is far more efficient, hence not requireing the large bitrates as fond in DV and HDV.
What we don't yet know is how well real-time AVC recording chips will work compared to the theoretical ideal of the AVC format, and what will happen when we try to edit AVCHD footage. I'm guessing we'll want to run AVC at at least 15 Mbps for professional purposes, and I wouldn't bet on that looking dramatically better than HDV.

If/when AVC cameras do become desirable it will take a while for editing solutions to catch up, and that may require converting to intermediary formats. So other than recording to something besides tape I don't see a huge change here, just another heavily compressed HD recording option. (The Panasonic solution to use up to 50 Mbps sounds more promising.)
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Old July 25th, 2006, 12:23 PM   #7
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It is just that the threat of "upto 24Mbs" might include these channels, and it might be limited to 18Mb/s, which is not insignificant, but still, with the more demanding modes might cause the quality to dip. While I appreciate that it may well be able to match HDV or exceed it a bit, 24mbs would be a worthy jump in quality fro all modes. As there is, the 15mb/s data rate may indicate what they plan for 1440&1080i, and that is lower then even 18mb/s, and I don't know how much of a real jump in quality it is, especially with all the movement we are planning on shooting.

Back to 24mb/s, maybe there is the possibility that with only two channels the video compression rate can be raised to 22.5Mb/s, which is a worthy compromise.

Douglas,
Quote:
Quote:
It could be that audio is in addition, or that the AVCHD video side might still be the original 18mb/s format, and less than what we were expecting.
This would be correct.
You seem to answer yes for both options ;). Are you meaning that the the audio is part of the 24mb/s stream, and the maximum fro video is 18mb/s?

There is a first impressions review at camcroderinfo up, of the SR1.

Last edited by Wayne Morellini; July 25th, 2006 at 12:24 PM. Reason: Wrong type of review.
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Old July 25th, 2006, 12:47 PM   #8
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perhaps it is like it is with DVD. DVD can have up to 9.8 mbits/s. DVD also supports 2 channel uncompressed or dolby audio. While 8mbits/s is usually the max video rate you can have if you want PCM you are not at all limited to that rate if you use dolby audio. If you want dolby stereo audio you very well could use 9 mbits/s.

The same may be true with AVCHD. If you use dolby audio you very well could record close to the 24 mbits/s max. I think it would be silly to limit the video rate to 18mbits/s just in case somebody does want to use 7.1 channels of PCM audio. The cameras hopefully will not do this. I hope they record at a higher video rate and if some crazy person does want to mix 7.1 channels of audio then they can re-encode the video to bring down the rate. Just like if you captured a DVD at 9 mbit/s and captured the audio as compressed but later decided to use PCM audio you would have to re-encode the video to fit.

If the bitrate is 18mbits/s then there are going to be a lot of wasted bits for those who are going to use 2 channel dolby audio.
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Old July 28th, 2006, 04:42 AM   #9
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the only time 7.1 is any use in camera, is when a camera is released with 7 XLR inputs... i doubt that THAT is going to happen any time soon.. more that likely its a wow factor marketing add on for the consumer..
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