GOP (IIIIIIIIIIIIII) dvd compatible or not?

[jfebus]

Hi All,

I have been given different opinions about using a GOP (IIIIIIIIIII).
If the GOP (IIIIIIIIIIIIII) dvd compatible or not?

Regards,

[SaSi]

I guess that you have mis-understood what a GOP is. If you consider a GOP being a series of I-frames, then it is not.

Presence of GOPs in an MPEG-2 stream is mandatory for DVD compatibility. A GOP is a series of pictures that MUST start with an I-frame and (for DVD compatibility) must have less than 20 frames. A subtle detail is that a GOP is not any sequence of frames between two I-frames. For such a series to be a GOP, there must be a GOP header before the GOP.

SVCD and VCD don't require this but DVD does.

The types of frames in a GOP can (theoretically) be any combination of I-frames, P-frames and B-frames.
I-frames are (more or less) like jpeg pictures.
P-frames are special frames (not whole pictures) that contain only the change in content from the last frame. The last frame can be an I-frame (whole picture) or a P-frame. (P stands for predicted).
B-frames are somewhat more difficult to understand. They contain the differences based on two frames, one to the left and one to the right of the current frame. Lots more can be said about them, but this is neither the place or the time. (B stands for Bidirectionaly Interpolated).

I think (have not read the DVD specs) that any GOP structure is valid for DVD.

Now on to what I guess is your actual question. Keep GOPs open or close them? (Many people confuse this question with the existence of GOPs).

A closed GOP is one where all frames have relations between them and with no other frame in the stream. The GOP starts with an I-frame and all subsequent ones are based on this or other frames following the initial I-frame.

An open GOP is one where at least one frame references frames in previous GOPs. If you wonder why this should happen, consider a sudden flash in the movie. Picture becomes white, however a few frames later, the same picture is repeated and an encoder may be smart enough to use a frame that can be out of the current GOP to base further predictions for frames.

An open GOP structure is more efficient in terms of size (perhaps a little slower to encode), but is considered not very editable (can't just cut anywhere for the fear that frames to the right will be orphaned). Also, chapter settings may suffer in some DVD players due to the same reason.

Closed GOPs are safer but less efficient in terms of size.

Both are supported and acceptable for DVD contents. (Closed GOPs are mandatory for multi-angle videos, where precice and smooth playback across angle crossings must be ensured).

Hope I made things clear, instead of more chaotic.

[jfebus]

Hi All,

I just tried again just to play safe and my Panasonic DVD player only played perfectly with capturing in GOP IIIIIIIIIIIIIIIII. I am using a vitec dcm card to do the capture.

Regards,

[Coopervid]

That's my experience,too.

Maybe despite all theories the standalone players are more tolerant than the rules. Personally I record with WINDVR2 from a Hauppauge WIN TV at 352x480, 5000 - 8000 kbit/s, I frames only, 48kHz sound. Perfect picture and movement (which is not the case as soon as B and P frames are enabled to have GOPs).
Cut the video, load in Ulead DVD MF2. No re-rendering, just creates the VOBs, burn and enjoy your DVD. The fastest way to do it with great quality.

[jfebus]

HI Coopervid,

So you were having troubles with the b and p frames! I though I was the only one in the world with those king of problems!

Were you able to play your I frames only dvds in several dvd players?

Regards,

[Coopervid]

jfebus,

I own only one player. It's a Daewoo 5700 and these DVDs work perfectly.
Maybe more people can just check it out. Basically the fastest way to get high quality / high speed movement MPEGs for putting on DVD without recompressing etc.

Vid

[jfebus]

Hi all,

Is anyone out there willing to help us out in the greatest quest of all time?

Is GOP (IIIIIIIIIIIIIIIIIIIII) compatible with DVD Players?

Regards,

[disturbed1]

Yes it is.

A GOP is a Group Of Pictures. DVD spec mandates that the length of a GOP must have a length less than 18 frames between I frames and no more than 2 B frames between P frames.


Since your capping with all I frames it satisfies this spec.

There's nothing wrong with capping with all I frames. The only downside is that it will have a larger footprint compared to a stream with P and B frames, as these frames hold most of the compression (talking about VBR of course).

On the upside, it's easier to edit, all GOPs are closed which makes it more compatible with lesser grade authoring apps.

[DJRumpy]

I would think the footprint would be MUCH larger. Your essentially tossing the key component to MPEG compression by excluding B and P frames. Encoded properly, a DVD should match your source very closely. An MPEG stream, at 9.8 Mb/s pretty much matches the source 1:1. A VBR MPEG-2 stream destined for DVD can do this as needed, although certainly most scenes won't require that much bitrate. Your just wasting space.

[bugster]

DJRumpy, I am certainly no expert on this, but logic leads me to believe you are mistaken that an mpeg that is I-frame only would take up more space than a more normal GOP (IBBPBBP...). For a given (average) bitrate they should be the same size. True, the picture quality will probably be different and I would expect I frame only to be lower quality. My reasoning is that with only I-frames to use, the amount of compression available is constant throughout the GOP, whereas a GOP with I, B and P frames can distribute the data better, allocating more to the I frames if needed and making up the loss of data available elsewhere with the use of mpeg motion prediction etc.

Am I making sense here???

Basically what I am trying to say is that it is bitrate that determines the size of any mpeg, Gop settings, resolution etc only affect quality.

Please correct me if I am wrong.

[jfebus]

Hi Bugster!

That's completely true...

I have tried diferent GOP Structures and all the captured files have the same size. It makes complete sence to me!

Regards,

[SLK001]

Is anyone out there willing to help us out in the greatest quest of all time?

Is GOP (IIIIIIIIIIIIIIIIIIIII) compatible with DVD Players?

I've told you twice already - a GOP consisting only of "I" frames may play on your DVD player, but you have not created a DVD complient stream. This means that you risk your video NOT playing on some other player.

The DVD spec specifically states that "Low Delay data streams are NOT allowed".

Also, the MAX size of a GOP for NTSC is 36 fields (18 frames) and 30 fields (15 frames) for PAL. Your stream of 21 "I"s would also not be DVD complient.

You need to ask yourself what are your goals? If creating only MPEG2 streams that play on your player, then what you are currently doing seems to work for you. But, if you are trying to make streams complient to the DVD spec that will play in ANY DVD player, then you are way off course.

[DJRumpy]

Huh?

but logic leads me to believe you are mistaken that an mpeg that is I-frame only would take up more space than a more normal GOP (IBBPBBP...)

Are you agreeing, or disagreeing? An mpeg that is all I frames, uses only the compression that I frames support (JPEG). By using B, and P frames, you allow the encoder to encode only changes from frame to frame (between keyframes), without wasting bits on 'no motion' areas. This results in a smaller file. If you clip is high motion, or noise, then the change is size wouldn't be as obvious as it would for say, someone sitting at a desk, giving a speech. This type of clip would get substantial benefit from B and P frames.

[jfebus]

Thanks SLK001!

I am really sad to hear that the only way for my Panasonic DVD player to play my videos is using a nonstandard gop structure...

will using a normal gop (IBP) and decreasiong the gop size to 4 give me the same results?

Regards,

[DJRumpy]

Has anyone done any quality tests on this? I would think the additional I frames would result in a higher bitrate requirment as well.

[jfebus]

Hi DJRumpy,

What about the average bitrate defining the file size!
I understand that using a I frame only gop will not use a higher bitrate in an specific I frame because it must "waste" bitrate in the other I frames. If you use B and P frames you can have a higher bitrate I frame. You will have a better distribution of the bitrate, but the file size will be the same!

Regards,

[DJRumpy]

If your using CBR, then changing to an I-Frame only encode would see no difference in size, as each frame get X number of bit's regardless (but quality would tend to suffer if a bitshortage resulted). VBR realizes the benefits of B & P frames. I should have been more specific.

Are you saying your player will not play with a standard GOP?

[jfebus]

Hi DJRumpy,

I have a Vitec DCM MPEG2 Capture Card and te only way I can get the captured files to play perfectly in my Panasonic DVD player is using a GOP filled with I Frames. I have noticed that decreasing the GOP size to 4 will give me near perfect artifact less movies.

regards,

[DJRumpy]

What encoder are you using, and what 'standard' gop structure did you try? Also, are you PAL, or NTSC?

If your card captures directly to MPEG, it may not be a standard 'compliant' mpeg. Have you checked the reference materials on the capture card to verify? I made the mistake of buy a non-compatible mpeg card...I ended up converting everyting via frameserve back to a compliant mpeg.

[jfebus]

Hi DJRumpy,

The wierd thing is that all my DVDs played perfectly in other DVDs (Sony, Samsung, Toshiba) but if I use then in a Panasonic ( Ihave tried 4 models) there are some artifacts (inthe same spot) when playing the clips.

If I chanege ti I frame only, the panasonics plays the clip perfectly!

Wierd right?

[bugster]

I know we are actaully off topic here but here goes anyway:

DJRumpy said:

I would think the footprint would be MUCH larger.

For a given bitrate, no. The size of an mpeg file is goverened entirley by the bitrate. Nothing else comes into it.


DJRumpy also said:

Your essentially tossing the key component to MPEG compression by excluding B and P frames...

This I agree with. Not using B and P frames severly limits waht the mepg encoder can do and you actually end up with something very similiar to motion jpeg (because, as you said, an I frame is compressed in a similiar manner to a jpeg).

So, for a given bitrate, I frame only mpeg's must compress each I frame MORE than would normally be the case and the opportunity for spreading bitrate around to where it is most beneficial is greatly reduced. So I guess there would be a loss of quality over a normal GOP (all other things being equal).

Does this make sense now?

Probably not, but what the hell does it matter anyway

[DJRumpy]

It does. I had to clarify as well. VBR would benefit from B & P frames over I frames alone. CBR would see no change, but quality would probably suffer, unless you had very high bitrates.

[groyal]

I'd like to add my US$0.02:

I have been given different opinions about using a GOP (IIIIIIIIIII).
If the GOP (IIIIIIIIIIIIII) dvd compatible or not?

It's unusual, but it's not incompatible provided higher-level rules are observed. In this case, a stream consisting of I-frames only has a GOP length of 1. DVD requires a sequence header ahead of every GOP, so you need to make sure your MPEG encoder is sending them at the correct interval (one for each I-frame).

In other words, a structure like this one is NOT DVD compliant:

<SEQ>[I][I][I][I][I], <SEQ>[I][I][I][I][I], ...

But a sequence like this one IS:

<SEQ>[I], <SEQ>[I], <SEQ>[I], <SEQ>[I], <SEQ>[I], ...

Every MPEG encoder is different in the way the sequence header control is labeled. Some are explicit ("output header every [X] GOPs"), some are implicit (you set GOP length=1 and it knows what to do), but any encoder intended for DVD MPEG-2 is going to have that control. Make sure your encoder has its GOP length=1 and header frequency=1 and you shouldn't have a problem.

[jfebus]

Hi,

Is there a way to verify the sequence control my mpeg2 encoder is using?

Regards

[DJRumpy]

I know reMPeg shows each gop as it scans the file. You could use it to directly view the gop structure of your MPEG.

[jfebus]

It does. I had to clarify as well. VBR would benefit from B & P frames over I frames alone. CBR would see no change, but quality would probably suffer, unless you had very high bitrates.

You are absolutely right!

I just encode using gop (IIIIIIIIIIIIIII) @ 4000(av) - 8500 (max) and quality was horrible!

Regards,

[SLK001]

In other words, a structure like this one is NOT DVD compliant:

<SEQ>[I][I][I][I][I], <SEQ>[I][I][I][I][I], ...

But a sequence like this one IS:

<SEQ>[I], <SEQ>[I], <SEQ>[I], <SEQ>[I], <SEQ>[I], ...

Unfortunately, this is mis-information, and is simply not true. The DVD spec is a subset of the wider MPEG2 spec. In the DVD spec, it calls out many requirements for a complient stream. Two of them are:
1) GOPs are NOT optional, and
2) Low delay streams are NOT permitted.

Both of the above streams violate both of these requirements, thus neither are complient.

But then, I've said enough here. You obviously want to keep asking the question until you get the answer you want to here. Sorry, but life ain't like that. I'm gone...

[jfebus]

Hi SLK001,

Where can I found a copy of the DVD Specifications?

Regards,

[SLK001]

Well, after you sign a NON-DISCLOSURE agreement with the DVD Forum group and send them a certified check for $5,000 US, your copy of the spec will be in the mail. I would check with them first before I sent in the check to make sure that they haven't had a recent price increase.

P.S.: Each additional copy that you aquire at the initial purchase, is only $500 US. So buy three for $6,000 US and stick one by your computer, one it the bathroom and one by your bedside!

[jfebus]

So everyone talking about DVD Compatibility is:

1) breaking the non-disclosure agreement

or

2) haven't read the DVD Specification