Info on Picture per Field details

[levick]

Sorry it this subject has been touched on a quick search did not present the details I hoped for.

I have now come across two video files that contain Picture per Field picture structure, I can encode to
Frame picture structure using Cinema Craft etc but has anyone any advise on re encoding in such away to retain the orginal Picture per Field conditions? I notice the Gops contain what appears to be 26 fields rather then the traditional 12-15 frames.
Any further information on this format would be appreciated.

[guns1inger]

Can you post a screenshot from g-spot 2.52beta ?

[levick]

Hopefully this will assist. As you can see Bitrate viewer shows the Pic Structure as Field and
GSpot shows a PPF status

[manono]

Hi-

...has anyone any advise on re encoding in such away to retain the orginal Picture per Field conditions?

I've seen a very few DVDs also with a Field Pic Structure, but maybe it's more common with PAL than with NTSC. It doesn't seem that CCE can do it, does it? My question is, why would you want to?

[levick]

What I was hoping for was the reasoning behind it, does it provide a better end result when encoded this way. It maybe able to be done with a hardware encoder only. I think my end result is to try and preserve the quality if this method of encoding is considered better then the norm.

[adam]

Its called field based encoding and it can achieve better quality when encoding interlaced content. My understanding is that it achieves better compression because the I frames are stored as fields instead of frames, so they take up less space. The only software encoder that I know of that can do it is Procoder. Field based encoding is not DVD compliant and its one of those things that most hardware players do not support. I've only tested 4 or 5 players with it but they all give a black picture unless you FF or RW.

If it were me I'd just encode this as a regular interlaced stream.

[levick]

Thanks Adam,

My first encounter is Pink Floyd's new "Pulse" dual DVD set. I consider this to be one of those
originals I want to put away from even finger prints. Gilmore went to alot of trouble to get the
best picture possible so I am told. This information lead me to asking.

Both my older Sony and currrent thinking NAD stand alone players cope however my son's 40" LCD TV does a real bad job of presenting this format. Re encoding as standard interlace improves the quality on his set only...most interesting. A lot could be said for the chipset in the Sony with respect to the presented information but we won't go into that here. The Yamaha DLP projector at work copes perfectly.

I agree with the encoding with regular interlacing conditions but can I do better......I just had to ask.

Again thanks for the information.

[adam]

Well if this was used on a commercial DVD than maybe field based encoding is allowed in the DVD specifications after all. Maybe its just Procoder's field based encoding that is non-compliant? I have no idea but I bet BJ_M does. I remember discussing this with him before. Maybe he'll see this thread, otherwise PM him.

[manono]

Well if this was used on a commercial DVD than maybe field based encoding is allowed in the DVD specifications after all.

It is. I was going to call you on that statement before, but you backpedaled. So I'lll just dispute these statements:

Its called field based encoding and it can achieve better quality when encoding interlaced content. My understanding is that it achieves better compression because the I frames are stored as fields instead of frames, so they take up less space.

Better quality? No. A field is a field, whether stored separately or as part of a frame. Less space? Probably very slightly more space, as there's an additional flag that tells which frames the fields belong to. I also know of at least one example where a movie on DVD is progressive 23.976fps and soft-telecined to 29.97fps, but the Pic Structure is Field. I don't really know if that's legal or not, but I suspect it is.

Lots of times I read of some musician or other wanting the best quality for his project, so he hires the best in the business to film his concert or whatever, but it then gets butchered by some fly-by-night DVD production house. Or it's originally PAL and gets ruined in the conversion to NTSC, or vice-versa. He doesn't have any understanding of that end of it, and doesn't know how to tell that his baby looks like crap. I don't know the DVD, and I surely don't know the DVD available in your country. Was it shot on film? It should have been. Was it shot interlaced with video cameras? Is it a lousy NTSC to PAL conversion, complete with blended fields? If so, why? If you want to put up a small section somewhere for us to have a look...

[BJ_M]

Well if this was used on a commercial DVD than maybe field based encoding is allowed in the DVD specifications after all. Maybe its just Procoder's field based encoding that is non-compliant? I have no idea but I bet BJ_M does. I remember discussing this with him before. Maybe he'll see this thread, otherwise PM him.

it is not dvd compliant and (as mentioned) , many dvd players will not play it ...


this was discussed here a couple of years ago i recall and i looked it up ... i did some testing also and found a very slight improvement for some interlaced sources - but wasnt really that great across the board (seemed to work very well for dv though)

[manono]

it is not dvd compliant ...

I beg to differ:

http://www.hometheaterhifi.com/volume_7_4/dvd-benchmark-part-5-progressive-10-2000.html

Here are some examples of what legal flag sequences look like...

However, it would be perfectly acceptable to encode that same sequence of film like this, using 10 MPEG pictures:

About a third of the way down, where you see Example 2 of the 3 flagging examples in the 3-2 Pulldown section. And I can point you to retail NTSC DVDs that use a Field Picture Structure.

[BJ_M]

you are not referring to the same thing we are -

and if a retail dvd did the encoding wrong - it would be not the first time ... plus it would not play on a number of players ... plus I looked it up in the $5000+ dvd specification book (which i dont have access to any longer) back then - and not much has changed since then ....

[manono]

you are not referring to the same thing we are -

I most certainly am. Example 2 will show as Pic. Structure: Field in Bitrate Viewer. Just look at the Picture Structure column, and then compare with Examples 1 and 3. It's perfectly legal.

The retail DVDs play fine in my player. If a player can't play it, I'd say there's something wrong with either the player or the Procoder created video.

[adam]

Manono, if you say field picture structure is dvd compliant than I have no reason not to believe you. But this begs the question, how do you encode to field pictures using anything other than Procoder? (manual comes right out and says that its field based encoding mode is non-compliant...and its true, it won't play on much of anything.) I'm sure there are encoders out there that can do it, but I'm not sure that any of them are at the consumer level, or whether there is even another software encoder with this ability. The original poster is using CCE and it definitely can't do it.

As for field pictures achieving better quality with interlaced sources, I was quoting Procoder's manual. I also tested the quality and found it to work wonders with DV footage. But I've seen numerous references to the fact that field pictures achieve better compression because only one field or the other (bottom or top) is coded as Intra, as opposed to the entire frame, made up of both fields, being coded as Intra in a frame picture. So it essentially costs you half as much for each I frame.

Here is a quote taken from an MPEG meeting for example:

With field-pictures, I-frames cost a lot less, since only one field is coded intra.

http://www.mpeg2.de/doc/luigi/mpeg2.htm

Also, 16x8 motion compensation is only available for field pictures. This samples a motion vector from each field, whereas a frame picture for those same two fields would only have a single motion vector sampled. Thus, if there are movements between the two fields, than using field pictures will help quality here as well.

http://viswiz.gmd.de/DVP/Public/deliv/deliv.211/mpeg/a_tool01.htm

The documentation that I see suggests that the ideal way to code interlaced footage is to use a combination of frame and field pictures. Field pictures are the default because they achieve higher quality on standard and fast motion. Frame pictures are used on slow motion/still images because it is more efficient in this case. Procoder actually has an auto setting that does this, but as has been said, hardware compatibility is virtually nonexistant.

Here's some more info, read the section titled, "Why encode as frames and fields?"

http://www.licensing.philips.com/information/mpeg/documents355.html

[manono]

Hi-

Manono, if you say field picture structure is dvd compliant than I have no reason not to believe you.

Don't believe me. Believe the Secrets Of Home Theater people. If they say it's compliant, you can bet it's compliant.

But this begs the question, how do you encode to field pictures using anything other than Procoder?

I don't, and I didn't claim to. All I said was that the retail DVDs encoded as field pictures play fine. You and BJ_M have said that Procoder encoded field pic DVDs don't play correctly. Not exactly the same thing. I use CCE, which turns them back to frame pictures.

With field-pictures, I-frames cost a lot less, since only one field is coded intra.

I hadn't thought of that. That makes sense, and I welcome the correction. Thank you. I was wrong to take you to task over it earlier, and I apologize. I know now that you said something very similar earlier. Had it registered then, I might have saved myself some grief.

Also, there was a lot of good information in that last link. Much of it I knew already, but some of it was new and useful to know. All of it was presented in a concise and easy-to-understand manner. I thank you again. The "Why Encode As Frames nd Fields" section seems to confirm that both field pic and mixed field/frame pic encoding is legal. I guess a lot of this discussion is academic because, as you say, there's no way to use field pic interlaced encoding in Procoder and produce something that can be played without problems on a standalone.

[levick]

Well gentleman and ladies if present, thank for the insight, for my next question to the experts.
What program would you consider the most accurate to determine the correct format for my mpeg files? I use GSpot of course. DG Index even Restream and Bitrate to try to give me the most comprehensive outcome. In some cases I get conflicting information from the different listed programes. A frame by frame check can normally detemine if intlerlacing is present. How ever, I have had what looks like a progressive file flag as Interlaced and the reverse is also possible.
Is it possible the flags can be inserted when the file is fact something very different?

I have only ever seen GSpot output a Picture per Field report, the other others with the expection of Bitrate show this as interlaced. Bitrate gives enough information to allow further investigation if one can read data correctly.

Cheers and again thanks.

[manono]

I have had what looks like a progressive file flag as Interlaced and the reverse is also possible.

You're a PAL guy, right? And you're talking about DGIndex telling you it's interlaced when you know it's progressive? If so, then you're talking about 2 different things. The vast majority of PAL movies on DVD are encoded as interlaced. The vast majority of PAL movies on DVD are from a progressive source. That's 2 different things, and the only way to tell what you have is with your eyes. I'm not sure what other kinds of conflicting information you might mean.

[BJ_M]

[quote="manono"]Hi-

Manono, if you say field picture structure is dvd compliant than I have no reason not to believe you.

Don't believe me. Believe the Secrets Of Home Theater people. If they say it's compliant, you can bet it's compliant.

But this begs the question, how do you encode to field pictures using anything other than Procoder?

I don't, and I didn't claim to. All I said was that the retail DVDs encoded as field pictures play fine. You and BJ_M have said that Procoder encoded field pic DVDs don't play correctly. Not exactly the same thing. I use CCE, which turns them back to frame pictures.


...................blah blah

[/quote


they never say it is compliant and you are reading thier article wrong -- what you are saying is that the DVD specifications are not correct (and canopus) --- which doesnt make a lot of sense...

[manono]

What part of:

Here are some examples of what legal flag sequences look like.

and:

However, it would be perfectly acceptable to encode that same sequence of film like this, using 10 MPEG pictures

do you not understand?

what you are saying is that the DVD specifications are not correct (and canopus) --- which doesnt make a lot of sense...

I've said no such thing. And you know it. I've never used Procoder. I've made no claims about it. I was just repeating what you and Adam said. I find no contradiction in saying that the DVD specs allow for field pic encoding, but, based on what you and Adam are saying, somehow Procoder isn't implementing it correctly. I'm getting a little tired of talking to you, so I'll retire from this discussion. Feel free to have the last word.