576i/25P ???

[GuanoLad]

We've just got the HVX202EN camera, and are experimenting with it a bit. But I have to say I'm confused by some of the nomenclature.

How can it be that you can use the i and the P in the same description? Is 576i/25P interlaced? Or progressive? What is it really telling me?

[GuanoLad]

Nobody answered this question for me, and we've just encountered it in a real situation and managed to record a two-camera shoot in different resolutions. Can anyone enlighten me - is 576i/25P progressive or interlaced, and why does it say both?

[SurJones]

It is the same for us USA peoples. we have 1080i/30p, If you have the manual, it explains it. I am sure Barry's book also might explain it.

[THoff]

It's progressively imaged video stored in an interlaced video stream. It is in fact progressive.

[GuanoLad]

Well, the manual says:
For output and recording, the 25-frame-per-second signal is converted to 50-field-per-second interlace. This mode gives you high quality images.

??? What's the point of Progressive mode then?

[THoff]

It is progressive. The recording format you are talking about, however, is interlaced. So the camera takes the progressively imaged video and writes it not as one progressive frame (because that's not supported by the recording format), but as two interlaced fields.

Whether the progressively imaged video is output as a single frame or two interlaced half-frames is inconsequential -- the output looks the same.

[GuanoLad]

*burble*burble* My brain just imploded.

[daveswan]

As THoff said, it's very simple realy, the image is captured as progressive, so you have a complete frame every 1/25th second, but this has to be split over two1/50th second fields, but they come from the same frame, so you don't have interlace problems.
When I capture this footage into Avid, I set the project type as PAL 25p.
BTW, the same thing aplies to the 1080 footge.

HTH,
Dave

[Cees Mutsaers]

Does this mean that in Avid (or any other NLE software) half of the fields will be thrown away?
As THoff said, it's very simple realy, the image is captured as progressive, so you have a complete frame every 1/25th second, but this has to be split over two1/50th second fields, but they come from the same frame, so you don't have interlace problems.
When I capture this footage into Avid, I set the project type as PAL 25p.
BTW, the same thing aplies to the 1080 footge.

HTH,
Dave

[mikkowilson]

No, all the information is kept.

Here's how it works:

The camera (in 25p mode) shoots 25prograssive frames every second. That's 25 true sigle exposures, with no interlacing.

However, the DV standard is 50i - that's 50 fields, or rather "half frames". So the camera takes this 25p, and records it as 50i. That is to say that it records each single prograssive frame as 2 half frames. The fact that the 2 halfs make a whole keeps the footage progressive. If you shoot interlaced, those two halves are always two halves, never w sing whole anything.

If you are dooing cuts only, and static graphics, you can edit 25p in a 50i project, or in fact with any 50i editor. That means (this is where 25p in PAL easily trumps 24p in NTSC) that you can edit 25p footage on ANY PAL editor. You can use 2 VHS decks if you want. or even from DV to BEtamax, to 2" tape if you really want. The picture will always be that 25p wrapped up cleanly in the 50i stream. Each 2i recorded frame is a 1p frame.

The only place where 20p/50i actually makes a difference is when new material is created or catured: The camera, ehen dooing wipes, motion effects, moving or animated graphics, etc.. It's beacuse of these little things that editing software shoudl be used in a "25p" and not a "50i" mode. But actual handling of the video signal is no different.
You can cut 25p DV in windows movie maker if you want!
This is also the reason that you can use a cheap "non-25p" camera as a capture deck. It's all DV.


So, in short:
576i/25p is a 576i line system native recording of 25p shooting. Yes it's true 25p, yes it's 100% DV compatible. No you arn't ever loosing anything, all the 25 prograssive frames you shot are there in all their glory.

- Mikko

[Barry_Green]

??? What's the point of Progressive mode then?
Just look at the footage. It's night-and-day different from interlaced.

[Cees Mutsaers]

Thus in the NLE system the 25 progresive frames are split into 2 times 25 frames. So on the timeline you have 50 frames namely 25 with the even and 25 with the uneven lines (of coarse in pairs) right??? If you load 25p recorded footage into the NLE you have to choose 25p (and not 50i) and internally the frames are split into the 50 half frames right?

But what happens when you after doing the edditing burn your project to a DVD? Are the 50 frames combined to 25 P frames again before it leaves the edditing system onto the DVD, blue-ray etc. ???




edit : in other words are you burning progresive images (25 full frames/sec.) on a DVD?

[mikkowilson]

The two halves (fields) of each frame always move together, regardelss if they are carrying a signal that was shot progrssivly or not.


- Mikko

[GuanoLad]

Thanks guys. I think I understand now. Or at least, I accept that 25P is truly progressive, anyway, which is what matters.

My suggestion is they don't confuse the issue by referring to it as '576i' and maybe just use '576' only.

[mikkowilson]

They have to still mark the recording standard as well as the shooting standard.
Sometimes it matters. (Don't ask when! [seriously.])

- Mikko

[mactrix]

576p or 1080p are visually progressive and it makes visually no difference compared to true progressive formats.

However the video information is stored in video lines but unlike interlaced video both video lines keep the same motion information. So you can say it is progressive.

Don't forget to setup your NLE timeline to progressive mode too.

[Barry_Green]

Thus in the NLE system the 25 progresive frames are split into 2 times 25 frames.

Not in the NLE, no. In the recording, yes.

In the NLE, they always group fields together into what they call "frames", even though they're not actual frames. But when working with 25p footage, they are actually, legitimately, truly frames -- you can set your NLE to work in a 25p sequence, with field order set to "none/progressive", and cut it as straight-up progressive.


So on the timeline you have 50 frames namely 25 with the even and 25 with the uneven lines (of coarse in pairs) right???
No, not really. If you were editing in a 50i timeline you'd still be dealing with 25 "frames" because NLEs don't let you edit at a field level; they always group fields together into field-pairs (or, more commonly, "frames").


If you load 25p recorded footage into the NLE you have to choose 25p (and not 50i) and internally the frames are split into the 50 half frames right?
If you put 25p footage on the timeline, you would be doing yourself a big favor to choose a 25p timeline. You could cut it on a 50i timeline and it would work, but any graphics or titles or transitions would look much better rendered at 25p than they would at 50i.



But what happens when you after doing the edditing burn your project to a DVD? Are the 50 frames combined to 25 P frames again before it leaves the edditing system onto the DVD, blue-ray etc. ???
You can render a 25p sequence from your timeline. But here it diverges from the way NTSC works. In NTSC DVDs you can export a true 24p sequence that will actually be encoded as 24p and live on the disc as 24p and played back as 24p (unless you're outputting to a CRT, in which case it'll split it back into fields and output fields with pulldown). I don't know if PAL DVDs can store a pure 25p signal or not; it may be that the output 25p from the timeline actually lives on the DVD as 50i. I'm not sure.





edit : in other words are you burning progresive images (25 full frames/sec.) on a DVD?
In 24P, yes. Not sure about 25p.

[Barry_Green]

My suggestion is they don't confuse the issue by referring to it as '576i' and maybe just use '576' only.
Completely agreed. On the DVX they never made mention of 480i/24p, they just called it "24p". On the HVX they went for "full disclosure"; it's probably caused more confusion than any other single item on the product.

[mactrix]

If you put 25p footage on the timeline, you would be doing yourself a big favor to choose a 25p timeline. You could cut it on a 50i timeline and it would work, but any graphics or titles or transitions would look much better rendered at 25p than they would at 50i.

Well, you would do it because if you add transitions to your 25p footage or you would animate position, rotation and so on the NLE would split the rendered part into fields - real visual noticeable fields.

But with graphics or titles it depends. If they aren't moving it makes no difference. If they are moving they get split into fields in 50i but depending on the movement it could look better than 25p on a CRT. You loose image resolution with 50i but you gain motion resolution. 25p on the other hand tends to shutter and it's difficult to create a smooth motion with animated graphics. You can reduce shuttering by adding a motion blur but than again you loose sharpness - equivalent with image resolution.




In NTSC DVDs you can export a true 24p sequence that will actually be encoded as 24p and live on the disc as 24p and played back as 24p (unless you're outputting to a CRT, in which case it'll split it back into fields and output fields with pulldown). I don't know if PAL DVDs can store a pure 25p signal or not; it may be that the output 25p from the timeline actually lives on the DVD as 50i. I'm not sure.

25p can live on DVD but it has do be flagged as progressive. Without the correct flag the DVD-Player will assume that the video is interlaced and will deinterlace it (for progressive presentation, e.g. on LCD or Notebook). Deinterlacing of progressive footage will look horrible and so you loose image quality due to the interpolation. A huge number of PAL DVDs, including Hollywood blockbusters don't have the flag. It's not a global flag for the whole DVD. Each MPEG-2 clip has to be flagged correctly. The progressive flag is similar to the anamorphic 16:9 flag. To add the flag to already encoded MPEG-2 clips you can use this helpful toolset:

http://homepage.mac.com/dvd_sp_helper/MPEG%20Append/MPEGAppend.html