Noise comparison: 35/4:2:0 vs. 180/4:2:2

[Piotr Wozniacki]

Lance, please give it a closer look (and on a really large display, too - your clients may be using huge displays):

- 100 Mbps is way too low for I-Frame Only. In this mode, I recommend 220 and up.

[Ron Little]

I do not know if this is of any help but here is a screen grab of the pre set from CS5.

[Dan Keaton]

Dear Friends,

I just returned from a 10-day business trip which included a 3D-Workshop.

It is hard to determine the official "Family Name" for Sony's PDW-700 and PDW-F800 cameras.

For the PDW-F800, they put "XDCam" on one line and on the next line they put "HD422" and list the codec as MPEG-2 4:2:2P@HL.

For the PDW-700, the Put "XDCam" on one line and on the next line they put "HD".

Both the PDW-700 and PDW-F800 use the same codec module, and we use the same codec module.

The white paper presented by Mark is from 2007, and it appears that was written before the introduction of the PDW-700 and PDW-F800.

Ron Little's post shows that Adobe CS5 makes a distinction between XDCam HD, XDCam EX, and XDCam HD422.


I know that for 720p we use a Group of Pictures (GOP) of 12.

As I understand it, for 1080, we use a GOP of 15.

If this is wrong and causing any problems, we will look into it.


We also use a "Closed Gop" and I feel that we should. Otherwise one GOP will depend of the images from the previous GOP.

We use VBR where Sony uses VBR. Otherwise we use CBR, the same as Sony, as far as I know.

[Luben Izov]

Adobe - Premiere Pro CS5: Third-party hardware compatibility

[Dan Keaton]

Dear Friends,

For 720p we use a GOP of 12.

For 1080p29.97, 1080p30, 1080i59.94, and 1080i60,we use a GOP of 15.

For other 1080i or 1080p frame rates we use a GOP of 12.

Thus 1080p23.976, 1080p24, 1080p25 and 1080i50 are a GOP of 12.

This information was obtained from our Chief Engineer.

[Rafael Amador]

Originally Posted by Dan Keaton

Dear Friends,

We also use a "Closed Gop" and I feel that we should. Otherwise one GOP will depend of the images from the previous GOP.

That means that any GOP will use his own I frame and the one before as reference.
Two "I" frames instead of one.
Thats GREAT.
Professional MPEG-2 software compressors by default uses Open GOPs.
rafael

[Piotr Wozniacki]

Originally Posted by Dan Keaton

We use VBR where Sony uses VBR. Otherwise we use CBR, the same as Sony, as far as I know.

Dear Dan,

My understanding is that XDCAM HD as used by Sony, has only 4 bitrates available:

- 18 Mbps (LP mode, VBR used to ensure maximum recording times)
- 25 Mbps (SP mode, CBR used to ensure compatibility with HDV)
- 35 Mbps (HQ mode, VBR used to ensure maximum quality)
- 50 Mbps (4:2:2 mode, CBR used to ensure compatibility with the legacy HD422 format)

Since nanoFlash can use higher bitrates as well, and their very purpose is quality - all Long-GoP modes above 50 (like 80, 100, 140 and 180) should be VBR, if this is only possible from the chip programming viewpoint. As no such modes exist in Sony XDCAM HD, compatibility is irrelevant. The average bitrate would give the user an estimate of the recording time in a given mode, while the maximum bitrate actually used by the chip could in all cases go as high as the CF card can handle.

I guess this is what someone called a "Constant Quality" mode earlier in this thread.

[Dan Keaton]

Dear Friends,

I get conflicting information when I search on-line for Open versus ClosedGOP's.

In some cases, they indicate that the Closed GOP does not referrence previous frames.

In other cases, they indicate that the "B" frame at the end of an Open GOP can reference the next frame, thus allows this one "B" frame to be slightly smaller. Tektronix's website lists this description.

What is a closed GOP? > Frequently Asked Questions : Tektronix

I feel that this is most likely correct and this is different than what I previously posted.

Since, if one is using our MOV or MXF files for editing, I feel that Closed GOP is better as it does not need the next GOP to decode the previous GOP.

But, for creating a DVD, and not editing, using Open GOP's may be ok.


Here is another link to a discussion of the differences:

GOP closed/open ???? What does it mean ? [Archive] - Doom9's Forum


Here is my position:

In some limited cases, such as when creating a DVD, without multiple angles, and without the need to fast forward, the Open GOP, offers some slight advantages.

However, when editing the files, I feel that Closed GOPs are definitely better.

I am reluctant to change from Closed GOPs to Open GOPs for a slight advantage, which may cause problems in editing our files.

If we decide to try Open GOP's it would require substantial testing on on part, with every editor and condition to prove that it did not cause problems, and this would distract us from delivering other features that have been requested.

This is a moot point when using our I-Frame Only files as this applies only to our Long-GOP files.

[Dan Keaton]

Dear Piotr,

For 50 Mbps and higher 4:2:2, we follow the Sony codec standards, which is CBR for compatibility reasons.

We have proven that we can increase the bit-rate, and the professional NLE's, other than Avid, handle our Long-GOP files at these increased bit-rates, and Avid handles our 50 Mbps Long-GOP files and all of our I-Frame Only files.

We have not (yet) proven that any NLE can handle the Sony 4:2:2 codec if we modify it to be VBR.

The Sony XDCam EX codec is VBR, thus we use VBR for that codec.

At some point in the future, we could experiment, but this would require quite a lot of testing to ensure that all NLE's will work with VBR.

At this time, we need to concentrate on the other features that have been requested and we have promised.

[Piotr Wozniacki]

Dear Dan,

I realize introducing VBR now would take a lot of testing; I just hope CD will keep such a possibility in mind when you are done with the more urgent things....

Thanks,

Piotr

[Mark Job]

Dear Dan:
The information I have at hand from Sony indicates realtime, one pass VBR to be part of the XDCAM HD standard. I still don't understand what type of encoder we have in our recorders from CF, but you wrote that it doesn't matter, so I'm assuming it could be done (??). Perhaps some experimental beta test software could be put out (Which I would be happy to test in my spare time to see what happens in Avid NLE with Long GOP and whatever ?

[Piotr Wozniacki]

Originally Posted by Mark Job

The information I have at hand from Sony indicates realtime, one pass VBR to be part of the XDCAM HD standard. I still don't understand what type of encoder we have in our recorders from CF, but you wrote that it doesn't matter, so I'm assuming it could be done (??).

This is exactly what I meant when stating:

Originally Posted by Piotr Wozniacki

Since nanoFlash can use higher bitrates as well, and their very purpose is quality - all Long-GoP modes above 50 (like 80, 100, 140 and 180) should be VBR, if this is only possible from the chip programming viewpoint. As no such modes exist in Sony XDCAM HD, compatibility is irrelevant.

And it certainly can be done, the 35 Mbps VBR being the proof....

[Gints Klimanis]

Do VBR files exist? May I have a special firmware that would allow my Nano to make them? I'll sign up as a tester for Sony Vegas - my regular platform.

[Piotr Wozniacki]

Gints,

The nanoFlash is already capable of VBR - in the XDCAM EX mode (35 Mbps).

[Mark Job]

Originally Posted by Piotr Wozniacki

Gints,

The nanoFlash is already capable of VBR - in the XDCAM EX mode (35 Mbps).

Dear Piotr: I suppose we have already at least one mode in which VBR is encoding away, so I should go test this. Personally, I've never used the EX Mode on my XDR. I guess it's time to go try it. :-) Isn't there also an 18 Mbps mode ?