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Old August 24th, 2011, 11:02 AM   #1
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HPX171 - Bit rates laid out.

Hello folks,

I have searched high and low on the net for a good reliable source of what bit rates the HPX171 records at in different modes. I have heard from one source that at 720p it is about 40mb/s, another tells me it's 100mb/s*, another tells me it depends if it's 720p or 720pn...

Furthermore I was difficult to convince that the DVCPro50 on the camera is definitely 50mb/s, and not some 'version' of DVCPro50 - the reason I was difficult to convince was because I was very very surprised to find that a camera of this level was capable of 50mb/s considering how much hoo-ha there is about achieving it with cameras of this level (EX3 needing a Nanoflash etc, the 305 being all the rage because it appears to be the first ever camera of its level that is capable of 50mb/s); but then I hear that the HPX is capable of not only 50, but 100! Surely not??

Does anybody know of a list, or is anybody able to very kindly compile such a list, of bit rates for every mode available on the HPX171? I really want to make absolutely sure that when I say I'm recording 50mb/s, that I am doing.

Any help very much appreciated. Thanks!

*What confuses me here is if 720 is 100mb/s and DVCPro50 is 50mb/s, why do they both take exactly the same disk space on the card?
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Old August 24th, 2011, 04:05 PM   #2
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Re: HPX171 - Bit rates laid out.

AJA has a free data rate calculator which includes DVC Pro codec data rates.
You can shoot at 100mb or 50mb. The manual is a free download at B&H and has all the data rate info.

Software - AJA Video Systems

Scroll down to the Data Rate Calculator.
Ed
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Old August 25th, 2011, 01:21 AM   #3
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Re: HPX171 - Bit rates laid out.

The 171 can record data rates that fast because of the P2 cards, it's not about the level of camera but the media it records to, which also happens to be fairly pricy. CF cards didn't become as fast as they are now until recently.
Because the codec used is intra-frame, it always allocates the same number of bits per frame regardless of any outside factors, this causes the bit-rate to change with the frame rate as more frames need more bits.

When shooting in a format that ends with "PN", the camera only records the frames it needs, whereas a camera without native shooting would always use up all the frames available to it. The end result is that you get better usage of storage space and longer record times.
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Old August 25th, 2011, 03:12 PM   #4
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Re: HPX171 - Bit rates laid out.

Thanks very much.

Just using the AJA data rate calculator now - I notice there is no 1440x1080 option? (I thought this is what the HPX170/1 used at 1080)? Any way of compensating for this?

Also I am assuming that at 8 bits to a byte, you just multiple the MB/s by 8 and that's your mb/s? For example DV50 is 7.11MB/s, which = 56.88mb/s?

Thanks
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Old August 26th, 2011, 05:34 AM   #5
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Re: HPX171 - Bit rates laid out.

The HPX171 records in 100Mb/s yes.

1080p/i = 100Mb/s

720 25p = 100Mb/s this is over 50p that's why it's 100Mb/s I think that this is because DVCpro wasn't created to record 720 25p only 50p (correct me if I'm wrong here please). Then Panasonic introduced P2 cards and with them 25pn which only records the frames it needs to, ergo 40Mb/s.

720 25pn = 40Mb/s

720 50p = 100Mb/s

Yes the camera has a strong codec for it's price point (100Mb/s, 4:2:2, I-frame). But it doesn't have a full raster chip - only 960x540 pixels - and the 1080 resolution is only 1440x1080 in PAL and even less in NTSC.
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Old August 26th, 2011, 07:51 AM   #6
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Re: HPX171 - Bit rates laid out.

Great, thanks very much for your help!
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Old August 26th, 2011, 11:09 AM   #7
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Re: HPX171 - Bit rates laid out.

I don't shoot DVCProHD, I use full raster AVC Intra 100 in my 370, so I'm
not 100% sure, but I would say when you see a data rate for DVCProHD,
it's taking DVCPro's 1440x1080 into account.

Here are a couple more, but they all come to the same conclusion... :-)
Ed

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