GOP "oddity" in HCEnc file

[AlanHK]

I occasionally use MuxMan, a freeware authoring app. It's fast and efficient for single-title disks. The author makes a big deal about how standards compliant it is.

Every project I've done with it using HCEnc-created mpegs, MuxMan reports a warning like:
Shortest GOP has 17 fields, longest GOP has 38 fields.
Fields: 368983, VOBU: 9935, Sectors: 2192760.
Largest GOP of 38 fields exceeds DVD specification of 36, resulting DVD is non-standard.
1 oddities detected, resulting DVD is non-standard.

However, other authoring apps don't complain, and I never have a problem playing a disk using these files. It may not be important, but I thought I'd bring it up.

[Mug Funky]

have you added soft pulldown by means of DGpulldown or pulldown.exe?

if so, the max GOP length is 12, and with HC it might be worth turning autoGOP off.

this issue has come up a few times before, but i'm not sure if there was ever a resolution.

[AlanHK]

have you added soft pulldown by means of DGpulldown or pulldown.exe?

if so, the max GOP length is 12, and with HC it might be worth turning autoGOP off.

this issue has come up a few times before, but i'm not sure if there was ever a resolution.

So is it a side-effect of pulldown? I guess that manufactures more frames, real or virtual I'm not sure.

The last time the AVI was 23.976 fps and I used HCEnc's pulldown. I've only use external pulldown with a file with a weird fps.

[Fishman0919]

I've gottin' this error before with Muxman with pretty much any encoder if you use a GOP of 15, CCE Basic/SP/SP2, Procode 2.... with HC w/auto GOP your going to get GOP's of 15

[Tropican]

Here's more or less "The Definitive" thread on this issue: http://forum.doom9.org/showthread.php?t=113143

Important Parts:

The GOP length restriction is based on displayed frames - not encoded frames.

Two max length GOPs (presentation period) has to fit within 1,2 seconds.

Two 15 frame encoded GOPs then pulldowned will display for 1,3 seconds

15 x 1.25 (the pulldown) = 18.75 gops = 38 fields = 38/29.97 (display time) = 1.26 seconds

(ref. DVD-3 5.1.1)
A VOBU represents a presentation period of at least 0.4 seconds.
A VOBU except the last VOBU of a cell shall represent a presentation period of at most 1 second. The last VOBU of a cell shall represent a presentation period of at most 1.2 seconds.

Meaning even though some "better" players handle these files fine, the DVD spec is done by displayed frames, so you are technically not DVD compliant over 12 GOPs w/ 23.976 pulldown video.

[hank315]

Nice of Philips you can download the verifier manual for free, it would even be better if the verifier program itself was free :D
But it's clear they're talking about displayed frames and not about encoded frames.
Although I never heard it caused playback problems it's better to stay DVD-compliant.
I will change the autogop behaviour so it will never output more than 36 fields when pulldown is active.
Simply setting the GOP length at 12 is a bit of a waste, 14 is also valid and will be better for some GOPs (IPBPBPB..).
Will be in HC020, HC019 is already finished and will be out soon...

[AlanHK]

I will change the autogop behaviour so it will never output more than 36 fields when pulldown is active.

Cool.

Will be in HC020, HC019 is already finished and will be out soon...

Maybe you should consider making that 1.0. I think it's well out of beta now.

[Mug Funky]

@ hank:

i don't have the DVD spec (wish i did), but the spruce manual says that soft pulldown'd streams can't go over 12 encoded frames per GOP anyhow. certainly the MPX encoders don't give you the option (whether "DVD compliant" is turned on or off) to enable auto-IVTC and have longer than 12 frames.

so perhaps if HC detects 23.976fps input it should set GOP size to 12.

btw, the philips verifier is very slow and gives not-very-useful results - a DVD encoded using purpose built hardware and pressed at a reputable plant will still give in the order of 200,000 errors and warnings, and take hours to scan.

i believe it has to be set up to be much less verbose, and only show errors of a certain kind, but this itself gives plenty of area for debate (ie, you could still have a non-compliant DVD if you ignore the wrong things).

[Tropican]

Simply setting the GOP length at 12 is a bit of a waste, 14 is also valid and will be better for some GOPs (IPBPBPB..).
Will be in HC020, HC019 is already finished and will be out soon...

Doesn't the GOP length have to be divisible by 3 for MPEG-2?

[hank315]

No, not necessarely, it can have any length between 1 - 15 (PAL) or 1 - 18 (NTSC), for DVD.
Normally running a IBBPBBPBBPBB... GOP scheme it will be divisible by 3 but other GOP schemes will have another structure like IBPBPBPB... with an optimal (PAL) length of 14.
Even something like: IPBB-IP-I-IBBP-IPBBPBB... is a valid MPEG2 stream.

[AlanHK]

Over at videohelp (http://forum.videohelp.com/viewtopic.php?p=1622667#1622667) this was discussed recently.

The advice given was:

The AUTO GOP setting in HCenc tries to select the GOP length (i.e., 12-2 or 15-2 etc.) and it seems to not be reliable.

For PAL you should always use 12-2

For NTSC you either have 23.976fps or 29.970fps

23.976fps will always be progressive and you should use 12-2

.. If your input is 29.970fps then you set the GOP to 15-2 regardless of what type of 29.970fps it is.

Now if you have 29.970fps that is 23.976fps hard-telecined to 29.970fps then you can perform an IVTC to get back to 23.976fps and this is best done in an AviSynth script (using the decomb filter plug-in). However if you do that then although the source is 29.970fps the script does an IVTC back to 23.976fps so in essence you are feeding the encoder 23.976fps progressive ... so you set it to 12-2 and perform the 3:2 Pulldown option (and then run it through DGPulldown to be "safe").
- John "FulciLives" Coleman

This should fix the long GOP problems.
Maybe the "autoGOP" function sholuld be amended as this?

[Boulder]

For PAL you can use 15-2 (or auto GOP) without problems.

[Sagittaire]

For DVD max GOP is 0.6006 sec:
- 15 frames (or 30 field) for PAL DVD
- 18 frames (or 36 field) for NTSC DVD

There are not min GOP and bframe can be adaptative

IIIBIPBPBBPPPPI are compliant GOP for example ...

[repi]

Hi,
I had another problem with MuxMan.
When I wanted to export m2v to VOB the error was "GOP contains more than 36 pictures".

So, I found the problem and it is in transcoding tool. There must be checked the option "Put Sequence Heaeder on each GOP".

BR
repi