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HPX170 & Uncompressed HD via HD-SDI.


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#1 ryan knight

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Posted 07 December 2009 - 09:33 PM

hey there shooters,

has any here done (or read about) anyone shooting with an HPX170 and recording uncompressed HD via the HD-SDI output to a Blackmagic or similar device?

thanks,

rk.
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#2 Phil Rhodes

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Posted 08 December 2009 - 05:06 AM

I've done it with various HDV cameras - the difference can be quite dramatic.

For instance:

First demo
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#3 Sam Martin

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Posted 01 January 2010 - 09:32 PM

The HD/SDI recording, bypassing the HDV/ P2 encoding, will render much better images. Go down this route if you have the right tools to do it for your job. You'll be impressed with the results, just as Phil's test footage shows....
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#4 ryan knight

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Posted 18 January 2010 - 11:53 PM

The HD/SDI recording, bypassing the HDV/ P2 encoding, will render much better images. Go down this route if you have the right tools to do it for your job. You'll be impressed with the results, just as Phil's test footage shows....


i really want to test it out with my accessible HVX, but i'm waiting to get my hands on the capture card required to record the uncompressed images to a hard drive.

in terms of hard drive space, how much larger, per minute, are the uncompressed files in comparison to the P2 dvcprohd files?

thanks,

rk.
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#5 Phil Rhodes

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Posted 19 January 2010 - 07:19 AM

in terms of hard drive space, how much larger, per minute, are the uncompressed files in comparison to the P2 dvcprohd files?


Quite a lot. You can work it out pretty easily in megs per second:

(height * width * bitdepth * samplesPerPixel * frameRate) / 8 / 1024 / 1024

The only thing that's complicated there is "samples per pixel". The short answer is that for 4:4:4 formats it's 3, whereas for 4:2:2 formats it's 2. The long answer is that that's the number of n-bit values you're storing per pixel on the screen; for 4:4:4, every pixel has three values, whereas for 4:2:2, every pixel has one and two halfs, if you see what I mean, which, when I went to school, was equal to two.

So, assuming 720p24 8-bit 4:2:2:

(720 * 1280 * 8 * 2 * 24) / 8 / 1024 / 1024 = 42.1MB/sec.

Not onerous. Certainly doable across two half-reasonable disks. This does not include the audio or the small overhead for the AVI or Quicktime wrapper.

The problem you may have here is that the only frame rates that commonly exist for 720p SDI are 50, 59.94 and 60. Usually, lower frame rates are interleaved into these with duplicate frames. The frames of interest are generally marked with RP-188 headers in the SDI stream, but your capture hardware must be capable of recognising this and behaving accordingly. Most isn't (it's much easier with 1080p). Also, I believe that the SDI output on the HPX170 is 10-bit. This is good, but you will need to pay close attention to how your postproduction workflow treats this data. It can be difficult to persuade some software to work in true 10-bit without truncating the data. Often it won't tell you that it's done this, and it can be hard to tell. You should evaluate whether it's worth recording at 10 if it's going to immediately get truncated in the first app you put it in.

In the interests of fairness, I should point out that DVCPRO-HD, as a codec, will not fail as badly as HDV did in my demos - it has a lot more bits to play with than HDV, even if the compression is not as clever.

P
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#6 ryan knight

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Posted 19 January 2010 - 10:41 AM

Quite a lot. You can work it out pretty easily in megs per second:

(height * width * bitdepth * samplesPerPixel * frameRate) / 8 / 1024 / 1024

The only thing that's complicated there is "samples per pixel". The short answer is that for 4:4:4 formats it's 3, whereas for 4:2:2 formats it's 2. The long answer is that that's the number of n-bit values you're storing per pixel on the screen; for 4:4:4, every pixel has three values, whereas for 4:2:2, every pixel has one and two halfs, if you see what I mean, which, when I went to school, was equal to two.

So, assuming 720p24 8-bit 4:2:2:

(720 * 1280 * 8 * 2 * 24) / 8 / 1024 / 1024 = 42.1MB/sec.

Not onerous. Certainly doable across two half-reasonable disks. This does not include the audio or the small overhead for the AVI or Quicktime wrapper.

The problem you may have here is that the only frame rates that commonly exist for 720p SDI are 50, 59.94 and 60. Usually, lower frame rates are interleaved into these with duplicate frames. The frames of interest are generally marked with RP-188 headers in the SDI stream, but your capture hardware must be capable of recognising this and behaving accordingly. Most isn't (it's much easier with 1080p). Also, I believe that the SDI output on the HPX170 is 10-bit. This is good, but you will need to pay close attention to how your postproduction workflow treats this data. It can be difficult to persuade some software to work in true 10-bit without truncating the data. Often it won't tell you that it's done this, and it can be hard to tell. You should evaluate whether it's worth recording at 10 if it's going to immediately get truncated in the first app you put it in.

In the interests of fairness, I should point out that DVCPRO-HD, as a codec, will not fail as badly as HDV did in my demos - it has a lot more bits to play with than HDV, even if the compression is not as clever.

P


it would be easier then to use the 1080/24PA function on the HPX, out through SDI? as supposed to 720 (i would prefer to shoot 1080 anyway), since 24P is recording into a 60i stream, with redundant frame removal upon capture.

how does this process change if i wanted to record uncompressed HD from the HVX, via the component out?

thanks phil, great answer!

rk.
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#7 Phil Rhodes

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Posted 19 January 2010 - 11:25 AM

The component out on the HVX looks absolutely rotten in my experience - very soft and mushy.

Otherwise, I suspect many of the same considerations would apply, including the 60p (not 60i) thing.

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#8 ryan knight

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Posted 19 January 2010 - 12:42 PM

The component out on the HVX looks absolutely rotten in my experience - very soft and mushy.

Otherwise, I suspect many of the same considerations would apply, including the 60p (not 60i) thing.

P


you have tried this process with an HVX? and it doesn't seem worth the extra time, trouble and hard drive space? what about the increased robustness when color correcting?

rk.
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#9 Phil Rhodes

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Posted 19 January 2010 - 12:52 PM

I've seen it done with an HVX and an S2 recorder, but I haven't side-by-sided it. My impression was that the HVX component out was very noisy, and while everything I've seen since has confirmed the view that the HVX is a somewhat noisy camera, I think the analogue outputs exacerbate it quite badly.

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#10 ryan knight

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Posted 19 January 2010 - 02:47 PM

I've seen it done with an HVX and an S2 recorder, but I haven't side-by-sided it. My impression was that the HVX component out was very noisy, and while everything I've seen since has confirmed the view that the HVX is a somewhat noisy camera, I think the analogue outputs exacerbate it quite badly.

P


i wonder, though, if this noise can be treated to be perceived as grain? and uncomp'ed HD from the HPX170 via SDI is not noisy? do you know how i could contact the guys who you know did the HVX workflow?

rk.
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#11 Phil Rhodes

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Posted 19 January 2010 - 06:20 PM

i wonder, though, if this noise can be treated to be perceived as grain? and uncomp'ed HD from the HPX170 via SDI is not noisy?


I think at some point you'd just have to try it. The 170 is reputedly less noisy than the HVX anyway (though I'm not sure as I haven't seen enough 170 material).

It wasn't so much a workflow as just a test - what sort of postproduction facilities do you envisage using?

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#12 ryan knight

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Posted 19 January 2010 - 07:06 PM

I think at some point you'd just have to try it. The 170 is reputedly less noisy than the HVX anyway (though I'm not sure as I haven't seen enough 170 material).

It wasn't so much a workflow as just a test - what sort of postproduction facilities do you envisage using?

P


i'm wondering if it's something that can be done using a high powered mac, like the red's workflow where you generate your own apple pro res dailies using redalert, and then do a conform back to the R3Ds for your DI in apple color.

your sample was with an HDV camera - which camera? also, do you have any footage online where i can see the comparison, or the uncompressed footage?

thanks phil,

rk.
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#13 Phil Rhodes

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Posted 19 January 2010 - 08:18 PM

I suspect a decent Mac could do it. Recording doesn't actually require much CPU horsepower, just big fast disks, and those aren't particularly expensive if you've got a bay handy to mount them in.

I don't think I have the original footage from that test; it was a few years ago. The camera concerned was a JVC GY-HD250. At risk of self-promotion, you can read about it here:

http://philrhodes.co...ite_data1.xhtml
http://philrhodes.co...ite_data2.xhtml

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#14 ryan knight

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Posted 20 January 2010 - 12:24 AM

thanks phil.

i'll read and enjoy your links, and probably have more questions.
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#15 Patrick Sherman

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Posted 20 March 2012 - 05:19 PM

The HPX170 outputs 1080i via HD-SDI regardless of recording mode correct? So for example if you selected 1080p24 in the recording menu the HD-SDI output will still be 1080i30. Isn't progressive better than interlaced? Probably silly question and just trying to understand the workflow better with the HD-SDI output.

I have it connected to my MXO2 but haven't really done much with it since I'm unsure of the footage issues I will run into.
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#16 Bruce Greene

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Posted 20 March 2012 - 06:29 PM

The HPX170 outputs 1080i via HD-SDI regardless of recording mode correct? So for example if you selected 1080p24 in the recording menu the HD-SDI output will still be 1080i30. Isn't progressive better than interlaced? Probably silly question and just trying to understand the workflow better with the HD-SDI output.

I have it connected to my MXO2 but haven't really done much with it since I'm unsure of the footage issues I will run into.

I've recorded 23.98fps over the hdsdi to an Aja I/o hd without problems. Does it improve the image over dvcprohd? Maybe...but this was to prores...
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#17 Patrick Sherman

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Posted 20 March 2012 - 06:54 PM

So regardless of the 1080i30 output of the HPX170 if you set your capture device to say 1080p23 that's what you will capture even though the camera is sending out 1080i30?
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#18 Bruce Greene

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Posted 21 March 2012 - 11:44 AM

So regardless of the 1080i30 output of the HPX170 if you set your capture device to say 1080p23 that's what you will capture even though the camera is sending out 1080i30?


Not sure about 1080 mode. And I don't think shooting 1080 with this camera buys you any additional image detail. (it has about 1/2 the resolution of a 720p Varicam due to sensor and lens)

The HDSDI outputs 720P 60fps with the proper frame flags for the "real frames". The AJA recorders and the Nanoflash can read these flags and only record the "real frames". The Panasonic recorders record at 60fps only, I believe, but also record the flags for frame removal in post software.
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#19 Patrick Sherman

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Posted 21 March 2012 - 01:25 PM

Not sure about 1080 mode. And I don't think shooting 1080 with this camera buys you any additional image detail. (it has about 1/2 the resolution of a 720p Varicam due to sensor and lens)

The HDSDI outputs 720P 60fps with the proper frame flags for the "real frames". The AJA recorders and the Nanoflash can read these flags and only record the "real frames". The Panasonic recorders record at 60fps only, I believe, but also record the flags for frame removal in post software.



Ahh Ok.. I was thinking because the SDI menu option in Camera has "AUTO" or 1080i or 480 as options that it only outputs 1080i or 480i.

That clears up my confusion. Appreciate it.
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