Ex-1 Ex-3 SDI Out

B

bayarea_dvxer

Member
Does the HD-SDI out work only while you are recording?
Or does it work also when you playback something on the card? And if you are playing it back from the card, wouldn't it be a reduced quality vs the live output?
 
HD-SDI will output when recording, playing back and while it's just on. Playing back from SxS will reduce from 10bit 4:2:2 to padded 8bit 4:2:0, which is the native recording quality.
 
Thanks devnull.
So, the SxS (35Mb/s or 25Mb/s) XDCAM long-GOP 4:2:0 gets converted to uncompressed 8bit 4:2:0 out of the SDI.
Is it creating or interpolating extra data than what's on the SxS in the process? Perhaps that's what you mean by padded.

When you can't capture live out of the SDI to take advantage of the 10-bit how big are the advantages to ingesting the uncompressed 8bit with a third party card vs just copying the long-GOP to a hard drive? Does anyone's workflow off-line edit and archive the long GOP, but then recapture via SDI for the final edit?

I know.. a lot of questions here.. thanks in advance for your replies.
 
It only reduces down to 8bit 4:2:0 when "playing back" as the prerecorded footage is coming off the SxS card.

If you are taking the live signal from the camera out the SDI output then it will always be 10bit 4:2:2.
 
It's a "signal" not a "format". A format is what get's recorded to the disc. A signal is the raw data coming out of the cable (like a DVI or HDMI digital signal). It's very high quality. But your'e correct in wanted to make sure to record in a format that takes advantage of it's high quality. You could record uncompressed HD. But it's data-rate is something like 1 GB per second! hehehe
 
bayarea_dvxer said:
Thanks devnull.
So, the SxS (35Mb/s or 25Mb/s) XDCAM long-GOP 4:2:0 gets converted to uncompressed 8bit 4:2:0 out of the SDI.
Is it creating or interpolating extra data than what's on the SxS in the process? Perhaps that's what you mean by padded.
Click to expand...
Well... understand that the output of the SDI port is always 10-bit, uncompressed, 4:2:2. So what is meant by it being "padded" is that the recorded 8-bit, compressed 4:2:0 is uncompressed, converted to a 4:2:2 color space, and then padded out to 10 bits. There's no new information being added, you're not getting "more" than you had on the SxS recording, but the SDI transport stream has to be made to comply with 10-bit 4:2:2. So think about it like you have a pint of water (on your SxS card) and you pour it into a gallon container (the SDI transport stream). You don't magically have more than a pint now, it just is carried in the gallon jug.

But when you try to capture or use that SDI signal, you're going to be working with a 10-bit 4:2:2 uncompressed HD signal. It just won't have as much detail as the live feed will have, because the XDCAM-EX compression will have discarded two bits worth of data and half the chroma resolution. So you won't be recording an 8-bit 4:2:0 signal, you'd be recording a 10-bit 4:2:2 signal which just happens to only use 8 bits worth of information and 4:2:0 worth of color.

Hope that makes sense.
 
Barry and Mitch,
Yes, that's VERY clear. This is why I think DVXUser is great. You can't easily find this type of info anywhere else. Thank YOU!

This also leads me to conclude there is very little reason to archive the huge, captured uncompressed files from SDI , since there no extra info there. Archiving the long-GOP 4:2:0 XDCAM is the same picture information in a much smaller package.
 
That's correct. You're very welcome. (I love this forum as well!)

This scenario reminds of back in the days when DV (DVCam and DVCPro) came out. A number of my friends were bragging about the fact that they had a 10-bit uncompressed capture card. They swore that by capturing uncompressed it was making their DV footage look better. In our case, we would move the DV footage into Final Cut Pro using firewire (something our competition couldn't do because they didn't have a DV deck with firewire) I my opinion, the firewire transfer always looked better than the DV to 10-bit uncompressed transfer because the signal didn't go from analog to digital, it stayed digital through the entire process.

Thanks for listening to the stories of an old production guy. hehehe
 
I'm trying to understand what Barry was saying. So basically we're not gaining much by capturing the signal live through the HD-SDI port since the camera records naively at 8bit 4:2:0, correct? Since HD-SDI has to comply with 10bit 4:2:2, it's padded to comply with the standards but as far as quality goes, it's still basically the same, right?
 
I believe:
* You do get the benefits of 10-bit 4:2:2 if you are capturing the material LIVE as you are shooting it.
* You only get the 8-bit 4:2:0 quality if you are captured pre-recorded content, playing out off the SxS card. The card doesn't capture the full information that the camera can offer if you take the live data.
 
Okay, so the camera is natively capturing at 10bit 4:2:2 but padded down to 8bit 4:2:0 for recording into the SxS card, correct?
 
Lor said:
I'm trying to understand what Barry was saying. So basically we're not gaining much by capturing the signal live through the HD-SDI port since the camera records naively at 8bit 4:2:0, correct? Since HD-SDI has to comply with 10bit 4:2:2, it's padded to comply with the standards but as far as quality goes, it's still basically the same, right?
Click to expand...

The live HD-SDI signal direct from the camera head is a true 10bit 4:2:2 HD-SDI signal, not padded at all. Straight, uncompressed, 1920*1080, 10bit, 4:2:2 from the signal processor.

Playing back previously recorded material from SxS, then out the HD-SDI is 8bit 4:2:0 padded out to 10Bit 4:2:2. It's the compressed long-gop mpeg2 data reconstituted to an uncompressed HD-SDI signal.

This is why devices like the Flash XDR recorder is popular with EX users. You can record the higher quality signal direct from the camera head at higher quality compression rates, bypassing the native SxS system.
 
Ahh! I suddenly see the light now. Once it's already recorded into the SxS card, by capturing the signal through the HD-SDI does not improve the quality as compare to capture it live and bypassing the SxS card play back.

I think I got it. Thanks for the clarification.
 
Lor said:
I'm trying to understand what Barry was saying. So basically we're not gaining much by capturing the signal live through the HD-SDI port since the camera records naively at 8bit 4:2:0, correct? Since HD-SDI has to comply with 10bit 4:2:2, it's padded to comply with the standards but as far as quality goes, it's still basically the same, right?
Click to expand...

No, you have to remember there are two different senarios here:

What comes out the HD-SDI when:

1: You are in MEDIA mode (ie play back a pre-recorded clip)
2: You are in CAMERA mode (ie live feed from the camera head)

Answer:

1: 8bit 4:2:0 XDCAM EX compressed image uncompressed and padded up into a 10bit 4:2:2 stream.

2: 10bit 4:2:2 uncompressed image from the camera head of the camera (this is the good stuff)

The only real variation on this is if you press the RET button in camera mode to play back the last clip (or part there off). In this case the camera is operating in the equivalent of MEDIA mode during that RET function.
 
Barry_Green said:
Well... understand that the output of the SDI port is always 10-bit, uncompressed, 4:2:2. So what is meant by it being "padded" is that the recorded 8-bit, compressed 4:2:0 is uncompressed, converted to a 4:2:2 color space, and then padded out to 10 bits. There's no new information being added, you're not getting "more" than you had on the SxS recording, but the SDI transport stream has to be made to comply with 10-bit 4:2:2. So think about it like you have a pint of water (on your SxS card) and you pour it into a gallon container (the SDI transport stream). You don't magically have more than a pint now, it just is carried in the gallon jug.

But when you try to capture or use that SDI signal, you're going to be working with a 10-bit 4:2:2 uncompressed HD signal. It just won't have as much detail as the live feed will have, because the XDCAM-EX compression will have discarded two bits worth of data and half the chroma resolution. So you won't be recording an 8-bit 4:2:0 signal, you'd be recording a 10-bit 4:2:2 signal which just happens to only use 8 bits worth of information and 4:2:0 worth of color.

Hope that makes sense.
Click to expand...

hey barry,
i'm still a little confused. if i was to use a Nanoflash or Flash XDR with an EX camera would i be getting a "true" 10 bit 4:2:2 image/signal? or will it be a padded 8 bit 4:2:0 signal/image?

thanks a lot,
Mike
 
The NanoFlash and XDR don't record 10-bit, they only record 8 bit.

The EX1's output is 10-bit, but the XDR and NF will downconvert to 8-bit before recording.
 
Okay, so what's the preferred device for 10bit SDI capture in the field? Is there anything that's practical at the moment? Or is it the SDI straight into a computer in video village land or on an Apple cart? The Aja IO?
 
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