DVD GOP Structure

[ta2]

Wasn't sure which forum to post in, so I chose this one. These forums are soooo complicated :P.

Okay, so here's my question:

If I use the TMPGEnc template for a PAL DVD, and change the GOP Structure to "I Pictures Only" will my DVD still be compatible with the 'DVD Standard'? According to another site...

"I picture only
Forces the encoder to produce a sequence of I frames only. Since the sequence contains only I frames each frame can be easily edited after encoding since there is no dependency on other frames. Also motion artifacts will be completely eliminated. Since the video sequence will not make use of compression provided by P and B frames a massive bitrate (perhaps 20Mbps) will be required to make the image look acceptable."

I am using of a bitrate of 4364KBits/sec, with all of the other quality settings at max, I can honestly say that I don't really notice any quality degredation (I copied the same frame from the same encode but with P Pictures aswell, and the difference was quite difficult to notice, however there was a little there).

Well, I've, yet again, made a simple question into a complicated one...

Here's the question again incase you've got lost in my nonsense...

If I use a GOP Structure of "I Pictures Only" will my (standalone) DVD player be able to play the DVD that I make?

Thanks

ta2

[FOO]

I think so. Try it. Why do you wanna do that ?

[ta2]

The compression speed is ~2.8 times faster if you don't use P frames.



To tell you the truth, I haven't got a DVD burner. I am just trying to find a quick method (relatively speaking) of converting AVIs to DVD MPEGs before I buy one, and it looks like I've succeeded at last!!!

[FOO]

It is a known fact that the "normal" GOP structure is more
efficient than I only. Less bits for the same quality.

[ta2]

It is a known fact that the "normal" GOP structure is more
efficient than I only. Less bits for the same quality.

Yes, but its not as fast by a long shot.

[Baldrick]

I'm moving you to the advanced conversion forum. The newbie forum is for us that don't care about settings and just encode and hope it looks good.

[BJ_M]

4300 is really to low for all I frame ... there would be so much degrad. that editing would be pointless ... we use aroind 30-40 meg/s min for all I frame and even then (but its a higher resolution also)...

if you want to edit later - how about a more compressed avi format or at least a IPPP frame mpeg2 ...

IPPP works pretty good - and is a sony standard and used by others also ... bit rate is ussually anywhere form 8000-15,000 for the lower end .. you could stretch that out to IPPPPP or just try it at 4300 ...

standard IPB GOP's are just better overall for dvd bit rates anyway ,,, though not as editable .

[ta2]

I have to say, I think it looks as good as the source footage (DivX DVDRip @ 640 x 272). I just want to know if my DVD player will be able to play it. I'm not 'that' bothered about quality, I just want it to be a fast conversion.

[FOO]

If it's a DVD just use DVDShrink. 15-20 minutes

[adam]

An I-Frame only mpg is not DVD compliant. Any given DVD player may or may not be able to play it. I strongly suggest you just use mpg the way it was intended. Using I-frames only is really silly, it defeats the purpose of mpg. It puts an incredible strain on the decoder, and chances are, yes you will get playback problems.

If you are looking for a way to speed up your encode then just use a faster encoder. TMPGenc is one of the slowest encoders on the market.

Also, when you say all other settings at max, are you also referring to the motion estimation? Because at highest level it takes about twice as long to encode, and most people cannot even see any difference. Just by dropping it down to high you will probably get the same speed increase as by using I-Frames only, but your file will still be compliant.

[FOO]

I had no idea. What is the minimum compliant GOP structure ?

[ta2]

An I-Frame only mpg is not DVD compliant. Any given DVD player may or may not be able to play it. I strongly suggest you just use mpg the way it was intended. Using I-frames only is really silly, it defeats the purpose of mpg. It puts an incredible strain on the decoder, and chances are, yes you will get playback problems.

If you are looking for a way to speed up your encode then just use a faster encoder. TMPGenc is one of the slowest encoders on the market.

Also, when you say all other settings at max, are you also referring to the motion estimation? Because at highest level it takes about twice as long to encode, and most people cannot even see any difference. Just by dropping it down to high you will probably get the same speed increase as by using I-Frames only, but your file will still be compliant.

Thanks, you've basically answered all my questions.

What other MPEG Encoder would you suggest? TMPGEnc is the only one that I have managed to create a useful outcome with. I have tried CCE , but I couldn't get it to use and templates I gave it.

Thanks

ta2

[ta2]

I just did a quick test with the motion search thing...

Highest 2:10
High 1:41 -22%
Normal 1:22 -37%
Estimate 1:14 -43%

The percentages are the percentages of time saved.



EDIT: This was a 1000 frame encode, and the times are in mins & secs.

[BJ_M]

i dont get it -- now you say your source is divx or xvid or something -- whats the point of converting it to mpeg2 for editing , then re-encoding ..

since the source is rather crappy in the first place -- leave it at that for editing , mpeg encoding is the last step ...
when you do use IPPP type encoding it is is for original source material .. not some downloaded crap ..

[flaninacupboard]

He doesn't want to edit the stream, the only reason that got mentioned is because he copied+pasted some info from another site.

All he wants is an increase in encode speed. for which he is willing to destroy the video quality. a more effective method would be to use a proper compliant GOP on a half D1 stream. so that's video at 352X480(or 576 for PAL)

This will give you a file with probably similar quality (if not better) as your I only encode, and still be much quicker as you're only encoding half the resolution.

[SaSi]

I just did a quick test with the motion search thing...

Highest 2:10
High 1:41 -22%
Normal 1:22 -37%
Estimate 1:14 -43%

The percentages are the percentages of time saved.



EDIT: This was a 1000 frame encode, and the times are in mins & secs.

If you want to speed up Tmpgenc, try using a motion search precision of "Lowest Quality". It will dramatically speed things up and not nececcarily give you "unacceptable quality".

At the same time, in settings, set DC Component precision to 8 bits, in GOP structure uncheck all three checkboxes (if any of these are checked) - the decect scene change is the one that forces additional processing delaying things - and in the Quantize Matrix tab, check the third checkbox "No motion search for still picture by half pixel" and also the check box below "Soften block noise".

Now, before someone argues with the settings above, theser are NOT optimal conversion settings. These are high speed settings. Depending on source material and bitrate selected, they can also give excellent quality.

For example, you can use the above settings with DVD quality video at 7Mbps and have excellent quality. With low resolution DivX material, you cannot expect high quality anyway and the settings above will not further deteriorate your video and also not waste time. For half D1, you could try with a 4500~5000kbps bitrate setting, prefferably dual pass VBR.

[flaninacupboard]

Just a thought, if you're only using I frames then surely no motion compensation is going on anyway, as there's no information carried between frames. no? does the MPEG encoder pack motion based info into an I frame anyway, even in an I only GOP?

[FOO]

No
if there's no communication with other frames, how can there be motion ?

[ta2]

I guess you're right about the motion thing, but someone said in an earlier post that a DVD encode with all I-Frames would probably not work.

So, from that, I have decided to use the 'standard' setting.

One question aswell...

Can anyone explain to me this:

When I load uip the template in TMPGEnc 'DVD (Pal)' The GOP structure is something like:
IBBPBBPBBPBB, but when I click on the 'standard' tab, it changes to...
IBBPBBPBBPBBPBB

Which one should I choose to make sure it is compliant with the DVD standard to PAL DVD players?

Thanks in advance.

ta2

P.S. I will try having everything on 'lowest quality' like SaSi said, but all I need to know now is what GOP structure to use out of the two above.

[mkelley]

You may be trying to make this way too complicated.

If you are looking at increasing encoding speed, then by all means use a different encoder. At "normal" settings for high quality (without changing a darn thing and just pressing the button) the MainConcept encoder encodes on my 2.4 P4 at real time -- 90 minutes for 90 minutes. The quality is superb, exactly as good even on a big screen as my source D1 footage, for all types and situations.

The MC encoder will cost you $150, but is worth every penny. There is even a batch mode so you can set up all your jobs and run them overnight. In this manner there really is no excuse to worry about encoding times.

[FOO]

I've yet to prove that I frames only is not DVD compliant,
but it is a fact that the DVD spec says:
18 frames max in a NTSC GOP.
15 frames max in a PAL GOP.

I like 15 for NTSC because that makes each GOP almost exactly 1/2 second.
(or 12 for NTSC Film)

[adam]

I-Frame only streams are called Low Delay streams, do a web search for more info.

http://www.mpeg.org/MPEG/DVD/Book_B/Video.html

Here is just one source confirming that low delay streams are not supported in the DVD standard.

I-Frame only mpgs are not DVD compliant.

[BJ_M]

they are used only in transport streams (afaik) (sometimes)

[qpskfec]

Even if I frame only is not in the DVD spec, a DVD player may still be able to play the stream. The DVD spec is a subset of the mpeg spec.

It depends on the mpeg decoder chip used. Many chip makers design the chips to be mpeg compliant so they can be used in other devices.

A few years ago, the mpeg chip in RCA DVD players was the exact same chip used by DISH/Directv sat receivers. The mpeg silicon was designed for MPEG2 MP@ML. For example, it could handle 15 mb/s versus the DVD max rate of 9.8 mb/s.

Since I-frame only is legal mpeg, it would up to the firmware of the dvd player to support it. It might also be the opposite that the designers would have to do something explicitly in the code to exclude I frame only operation if the mpeg decoder supports it.

I expect that many dvd players would support I frame only, but would not be surprised if some don't.

[ronnylov]

Can anyone explain to me this:

When I load uip the template in TMPGEnc 'DVD (Pal)' The GOP structure is something like:
IBBPBBPBBPBB, but when I click on the 'standard' tab, it changes to...
IBBPBBPBBPBBPBB

Which one should I choose to make sure it is compliant with the DVD standard to PAL DVD players?

Thanks in advance.

ta2

P.S. I will try having everything on 'lowest quality' like SaSi said, but all I need to know now is what GOP structure to use out of the two above.

Both are compliant on a PAL DVD. Maximum GOP is 15 frames. The first one has 12 frames and the other one has 15. I frames need most bitrate, P frames less and B frames the least bitrate. So if you are encoding at low bitrate the 15 frame GOP may give better quality.

[SaSi]

An interesting experiment with GOP structure would be to alter it.

You need to have an I-frame (and sequence with GOP header) every 15 frames tops, but the DVD specs don't dictate the actual mix of B and P frames.

For example,

IBBPBBPBBPBBPBB is legal and has 1 I-frame, 10 B-frames and 4 P-frames.

As I-frames use most bitrate, P less and B-frames the least, it is feasible to get better results with:
IBBBPBBPBBBPBBB

This structure contains 1 I-frame, 11 B-Frames and 3 P-frames. However, you need good motion search to achieve the desired result (better picture for a given bitrate) because otherwise the B-frames will start to grow in size out of control. It depends on the encoder and the motion search setting - which defeats the speed improvement.

Another option is to have Tmpgenc perform a scene change scan of the source video (whicl will generate a list of where I-frames should be placed). This can dramatically help it cut GOP structures short (less than the preset 15 frames) and insert I-frames in every scene change. I have found that it makes a difference only if you encode with 2 pass VBR settings.

Note that the time it takes Tmpgenc to scan the source AVI for scene changes is significant.

[BJ_M]

putting 3 B frames together is not ussually a great idea at all - but multiple P frames togther is ok but of no use at lower bit rates --

see "MPEG-1 and MPEG-2 Digital Video Coding Standards" McGraw Hill Publishing Company

[Cornucopia]

So the real question about DVD compliance boils down to:

Is an I-frame only GOP structure = Low Latency

If it is, it's non-compliant, if it isn't, it can be compliant as long as each I-frame is it's own GOP.

Looking at some sources that I was able to get my hands on:
Scenarist docs, Maestro docs, DVD-Demystified book and website, other hardware and software encoder docs...
It still seems unclear whether this is "not allowed" or just "not recommended" cuz of bitrate/quality concerns.

Anybody with a good definitive final word?
(adam, sorry but that link doesn't specifically say that I-frameOnly=Lowlatency, otherwise I would completely agree with you)

Scott

[SaSi]

If I understand correctly, a low delay stream is one that has no B-frames. Such frames are low delay since they don't have to buffer B-based pictures and display them out of decoding order.

Now, if a low delay stream is not permitted, that implies that DVD compliant streams must have B-frames.

Is that an answer?

[Cornucopia]

But that would mean that [IPPP] type GOPs wouldn't be allowed, and I know that those are.

Scott