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Old September 10th, 2003, 06:02 PM   #1
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miniDV data rate

I'm trying to understand the data rate for miniDV.

I have seen charts listing miniDV at a rate of 25mb/sec. The avi files I capture from my GL2 camera are at 3.6mb/sec. Is the resolution loss as significant as these numbers would indicate, or is it a compression factor.

I use a Canopus capture card on a pretty robust pc.

What am I missing?

Thanks,

Kasey
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Old September 10th, 2003, 06:13 PM   #2
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Are you sure you're comparing bits and bytes ? DV25 is 25 MBits/second.
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Old September 10th, 2003, 06:34 PM   #3
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That probably makes sense. My ignorance is revealed more with every item I post.

Thanks,
Kasey
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Old September 10th, 2003, 08:56 PM   #4
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psst... 25megabits/second doesn't translate into 3.6megabytes/second.

Anyways the audio is uncompressed and the video is compressed 5:1. There's other random stuff that takes up space (time of day, timecode, file headers, etc.)

Adam Wilt's DV FAQ is pretty comprehensive on this. Check out the pictures section for information on the bad things that might happen due to DV compression. DV is kind of like high quality JPEG. It's also in 4:1:1 color space so the color resolution is not as great as DVCPRO50, digibeta, etc.
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Old September 10th, 2003, 09:31 PM   #5
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> psst... 25megabits/second doesn't translate into 3.6megabytes/second

It's pretty close, but I would have guessed that storing the data on the disk may have some overhead. Anyway, thanks for the pointer to Adam Wilt's FAQ. So, DV25 is actually 29 MBits/second.

Here's the link:
http://www.adamwilt.com/DV-FAQ-tech.html
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Old September 10th, 2003, 10:04 PM   #6
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Just for general clarification, Bit (Binary digIT) is binary number in base 2, either a one or zero. Byte is a unit of memory consisting of 8 bits.

Bit Rate: Bps, Bytes per second, 8 bits bps, bits per second. Bit Rate is measured in bits per second (8bps = 1Bps). It is used to express the rate at which the compressed bitstream is transmitted. The higher the bit rate the more information that can be carried.
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Old September 10th, 2003, 10:20 PM   #7
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Computer industry practice is MBytes or MBits. The former may be either Million (1,000,000) /Thousand or Mega (1024 x 1024)/Kilo (1024) . For most digital equipment, it Mega/Kilo. The disk drive industry decided to use Million to inflate the size of their drives.

Since too many people inadvertently swap bps and Bps, it's more common and reliable to write out the entire word.

There is also a difference between data rate and transmission rate. For example, many serial 8-bit interfaces use one stop and start bit for a total of 10 bits transmitted to carry 8 bits of distilled data. In that case, the serial bit transmission rate must be divided by 10, not 8, to yield the actual data rate.

We can look forward to many industry reuses of older terms.
If you ask my father, a retired IBM memory designer that was
present for the first memories, he'll tell you a byte was originally nine bits.
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Old September 10th, 2003, 11:30 PM   #8
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Binary is simple once you learn to understand it. Its much easier to understand when a teacher teaches you. I learned it in my computer switching/networking techschool for the air force.
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