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AVCHD Format Discussion
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Old July 20th, 2006, 05:05 AM   #1
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HDR-UX1 and HDR-SR1 Bit Rates

Reading from the long thread about these new camcorders, people are upset at the "low" bit rates of 12Mbps and 15Mbps for the UX1 and SR1 respectively.

I want to clarify something here. Unless I am mistaken, unlike HDV, AVCHD encoding is VARIABLE bit rate. So instead of being fixed at 25Mbps like HDV, the encoder in AVCHD evaluates the complexity of the scenes and adjusts bit rate appropriately.

On the specifications on the Sony Japan web site it does mention the bit rate as average - VBR, see:-


So for the SR1, 15Mbps is only the average bit rate and I am sure on complex fast moving speeds it goes much higher.

In fact I did some calculations and came up with an average bit rate of 15.89Mbps (for both audio and video). This is how I calculated:-

The HDD is 30GB. But for Hard Drives it is not Giga Bytes but "Billions of Bytes". Then I took the 4 hours and 0 minutes as the recording time. Note again that it says “approximate” record time on the specifications again proving that the bit rate is not fixed but indeed VBR.

So when you divide 30,000,000,000 by 14,400 seconds you get 15.89Mbps.

In conclusion, the bit rates are not far off from HDV. And if you take the amazing compressibility of the MPEG-4 AVC codec into account, it should more than likely exceed the picture quality of HDV.
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Old July 23rd, 2006, 10:02 PM   #2
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Bitrate's not the only issue...

The fact that the highest-quality bitrates of HDV and AVCHD are similar, and that AVCHD is using a more efficient compression algorithm, doesn't necessarily mean that the quality of AVCHD will be better than HDV. AVC/H.264 is far more compute-intensive than the MPEG2 compression used in HDV, so the built-in hardware compressor in Sony's AVCHD camcorders will have to work a lot harder than the compressor in HDV cameras. Frankly, I doubt that AVCHD will look as good as HDV in comparable circumstances, but I'm certainly withholding judgment until production models of the UX1 and SR1 are tested.
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Old July 24th, 2006, 07:17 PM   #3
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I agree, I doubt AVCHD will look as clean as HDV, and I also doubt this will be used in a 'professional' format. This will most likely stick to a consumer-only lineup. With HDV, the video quality is still very (subjective) good, yet is difficult sometimes to work extensively with in regards to color corrections and other editing techinques and certain conditions (such as fast motion). This is due to compression, and I think AVCHD is the opposite direction most professionals want to go in, UNcompressed HD would be ideal, to allow the most data to play with and mold into what picture one wants to accomplish. Especially with the UX1, that is a camcorder that will be all but worthless to anyone down the road (IMHO) if Blu-ray dies, (from my understanding HDDVD players will not recognize the video on the disc) and will be INCREDIBLY difficult to edit due to the compression and encoding on the DVD...the SR1 however at least will make it a little easier to transfer video onto whatever format the consumer wants, but with HDV you can do the same, just without the harddrive...

To make an incredibly long winded comment shorter...I'm not excited at all about AVCHD as a format for proffessionals, and I find it unneccesary for consumers...
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Old July 25th, 2006, 04:05 AM   #4
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HDV is a consumer format they use in prosumer cameras, AVCHD is a consumer format allowing HD in DVD cameras, but also in prosumer cameras, if they wish.

Have a look at this thread on the 6Mb/s of 7.1 audio, asking where it is going to go, and if into the 24mb/s:

For the DVD cameras, Doubly consumes 64 - 640kbps, which makes the 30GB time closer to 15mb/s. But they say approximate a lot of the time so they don't have to say 15.840128MB/s etc as well.

The SR1 link has a VBR in it, which might mean that though variable, approx 15Mb/s is the max rate. We have had this sort of discussion in the XDCAMHD thread sometime ago, and it appears this is the way it went, though I would love it to be wrong ;). But, I take your point, the google translation says "average" bit rate, but is that the right translation (or correct information on the web page) could it be "averaging bit rate" which would imply a function rather than quantity to the VBR.

I don't know the chip in the camera yet, but this company here:


Is supposed to be supplying the chips for a number of cameras, and promise comprehensive H264, and have mentioned over "15Mb/s) before. There chip for consumer recorders is very cheap, revolutionary and low powered, with an array of processors that do the H264. The Professional version of the chip consumes heaps more power at about 1 W. The Japanese are said to be impressed with the design.

I think that at 15mb/s it can operate suitably against HDV, but requires upto 24Mb/s to operate suitably more than HDV.
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Old July 26th, 2006, 10:33 PM   #5
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Found the answer, I asked Kaku from Japan, on another thread, and he has told me that the word translated as average really means approximate. "approximate" doesn't really indicate either way though, but I would be happy if it did go to 24mbs as needed.

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