Can Someone Explain GOP?

[J3M]

Can someone explain or point me to a resource that explains, in detail, what GOP means?

[SLK001]

Did you use our glossary?

https://www.videohelp.com/glossary

[J3M]

No, I did not. I did search through the forums though. Sorry, and thanks!

[indolikaa]

Now that you know what Group of Pictures is, let's begin one of the more-popular flame wars on this forum, shall we? I'll start.


Anybody who uses Open GOPs doesn't know his head from his left testicle! (Or ovary, if you are so configured.)

Open GOPs forces a change in the method by which discrete-cosine transformation is calculated, causing the final MPEG stream to have bit-level errors in the P-frames.

[J3M]

No need to start a flame war. I just see posts saying what P frame or whatever they use, and while I knew this had something to do with GOP settings, I didn't understand the reasons behind it. Actually, after reading the glossary, I still don't. I better understand what it is, but not why one setting is better than the other.

I read LordSmurf's stuff and just set mine to 2 and 2 and used closed GOP's. Seems to work just fine. However, I read a thread a few days ago that was talking about the max settings and such, and that got me wondering what this was all about in detail.

See, I'm getting ready to start converting a lot of home video footage to DVD. I've been taking it slow so I could learn as much as possible and play with what settings worked best for me before undertaking the rather large project.

So, let me ask this as a reference. In MMC, what is the difference between setting GOP from 2 and 2 to 4 and 4, for example.

[indolikaa]

I was kidding J3M. At least you didn't ask which format was better: Minus R or Plus R.

It's primarily a horsepower issue. I've never understood it fully, but the more B/P frames you request, the more horsepower is required to calculate the progressing changes from the original I-frame.

[J3M]

I thought it was hyphen R, not minus? Just kidding.

Ok, so if you have a very fast CPU you could up the GOP settings? If so, what advantage does this give you?

I'm sorry if these are stupid questions. It's not enough for me to just set something because someone says it's the best. I prefer to learn the "why's" and then make up my own mind.

[SLK001]

Humm... Well, here's my gallon of gasoline (or petrol, or benzine) to through into this fray.

Closed GOPs require all information to be kept in the GOP, thus causing larger file sizes. Open GOPs allow reference frames to exist outside of the current GOP. I have never heard of this "Open GOPs forces a change in the method by which discrete-cosine transformation is calculated, causing the final MPEG stream to have bit-level errors in the P-frames" thing.

A couple of years ago (late 2001 to mid 2002), someone wrote a very good description of GOPs (maybe adam or vitualis). For some reason, the search engine doesn't go back any farther than early 2003.

[indolikaa]

I have never heard of this "Open GOPs forces a change in the method by which discrete-cosine transformation is calculated, causing the final MPEG stream to have bit-level errors in the P-frames" thing

No, I was kidding about that, too.

A couple of years ago (late 2001 to mid 2002), someone wrote a very good description of GOPs (maybe adam or vitualis).

I was thinking the exact same thing. Adam was my guess.

[SLK001]

Here's a good blast from the past reference.

https://www.videohelp.com/forum/archive/t48574.html

[indolikaa]

Thanks!

I still make tons of VCDs. This is interesting reading material. I always just capture and burn MPEG-1, I've never thought to play with the stream much. Hmmm, maybe some experimenting tonight.

[J3M]

Thanks guys! I appreciate the info. Looks like I've got some playing around to do this weekend as well.

I'm leaving for Arizona in two weeks and will be coming back with a lot of footage. I was hoping to have the best settings figured out by this time. Well, by best I mean the best ratio of quality vs. file size. My last capture I did was 1 hour 40 minutes worth of vacation footage, captured at 720x480 Mpeg NTSC using LPCM for audio. The file size was over 6 gb!

[lordsmurf]

GOP is the temporal compression algorithm. I-P-B ... whereas I is the main image, and the P and B reference off one another and the main image.

My usage of 2-2 is specific to my usage of the templates for cartoons, as it relates to the live MPEG capture done by ATI MMC. My concern is for quality over compression. I noticed less artifacts by moving it to 2-2 from the standard delta pattern 4-2. These artifacts are MOST noticeable on cartoons. I don't see much difference on live material unless it has large areas with visual content similar to a cartoon.

The compression change from 2-2 to 4-2 is honestly quite small anyway.

Some versions of TMPGEnc DVD Author on some systems whines when the GOP is not closed delta 4-2.

When encoding after-the-fact, go for 4-2 .. which allows better compression. Many hardware encoders already do their own thing, whether it be 2-2, 3-2, 4-2 or dare say 5-2 or more.

Open GOPs allow for higher compression by referencing between GOPs. However, many authoring applications do not like open GOPs, including professional ones. From this action, I infer that DVD was never meant to have open GOP, but it was more likely an oversight by the DVD Forum when aligning the specs allowed.

I always use closed. For cartoon captures, I use 2-2 ... for live captures, I use 4-2, 3-2, or 2-2 depending on bitrate ... and for encoding, I always use 4-2 in TMPGEnc, don't remember the option being in Procoder, I leave MainConcept settings alone normally.

[FOO]

Open GOPs make it harder to edit mpeg2

[DVDDave]

What is better-- -R, or +R???

Thanks!!!!!!!!!!

[indolikaa]

Neither, Dave. Everybody knows VCD is kind and DVD is shite.

[BJ_M]

i use both open and closed in commercial dvd's - Closed around scene changes and open elsewhere ... that way the GOP lenth is not fixed.

for example - here is a begining of a film and a bit further along ..

Gop no.,Timecode,Pic n.,Pictures,Closed,Broken l.,Has seqHdr, offset
1,00:00:00.00,15,IPBBPBBPBBPBBPB,Yes,No,Yes,000005a
2,00:00:00.15,15,IBBPBBPBBPBBPBB,No,No,Yes,0244777
3,00:00:01.00,8,IBBPBBPB,No,No,Yes,0488e93
4,00:00:01.08,8,IBBPBBPB,No,No,Yes,05d3e16
5,00:00:01.16,6,IPBBPB,Yes,No,Yes,07077a9
6,00:00:01.22,5,IPIPI,Yes,No,Yes,07f4599
7,00:00:01.27,9,IPBBPBBPB,Yes,No,Yes,08bb073
8,00:00:02.06,5,IPBBP,Yes,No,Yes,0a19b45
9,00:00:02.11,12,IPBBPBBPBBPB,Yes,No,Yes,0ada188
10,00:00:02.23,1,I,Yes,No,Yes,0cabacc
11,00:00:02.24,5,IPBBP,Yes,No,Yes,0cd3aeb
12,00:00:02.29,9,IPBBPBBPB,Yes,No,Yes,0d9587c
13,00:00:03.08,3,III,Yes,No,Yes,0ef2366
14,00:00:03.11,5,IPBBP,Yes,No,Yes,0f6707a
15,00:00:03.16,6,IPBBPB,Yes,No,Yes,102a170
16,00:00:03.22,4,IPBB,Yes,No,Yes,1114068
17,00:00:03.26,11,IPBBPBBPBBP,Yes,No,Yes,11af05d
18,00:00:04.07,10,IBBPBBPBBP,No,No,Yes,1357f6a
19,00:00:04.17,15,IPBBPBBPBBPBBPB,Yes,No,Yes,14dac73
20,00:00:05.02,15,IBBPBBPBBPBBPBB,No,No,Yes,171ed1b
21,00:00:05.17,15,IBBPBBPBBPBBPBB,No,No,Yes,1963697
22,00:00:06.02,15,IBBPBBPBBPBBPBB,No,No,Yes,1ba80e2
23,00:00:06.17,15,IBBPBBPBBPBBPBB,No,No,Yes,1dec4eb
24,00:00:07.02,15,IBBPBBPBBPBBPBB,No,No,Yes,2030c27
25,00:00:07.17,15,IBBPBBPBBPBBPBB,No,No,Yes,2275251
26,00:00:08.02,15,IBBPBBPBBPBBPBB,No,No,Yes,24b9b2e
27,00:00:08.17,15,IBBPBBPBBPBBPBB,No,No,Yes,26fdf90
28,00:00:09.02,15,IBBPBBPBBPBBPBB,No,No,Yes,29425dd
,.
.
.
.
.
.
.
170,00:01:20.00,15,IBBPBBPBBPBBPBB,No,No,Yes,16aec7c8
171,00:01:20.15,15,IBBPBBPBBPBBPBB,No,No,Yes,16d30ba4
172,00:01:21.00,14,IBBPBBPBBPBBPB,No,No,Yes,16f75ae0
173,00:01:21.14,4,IIII,Yes,No,Yes,171af853
174,00:01:21.18,4,IPBB,Yes,No,Yes,1724377e
175,00:01:21.22,7,IPIIIII,Yes,No,Yes,172d9a01
176,00:01:21.29,12,IPBBPBBPBBPB,Yes,No,Yes,173e470e
177,00:01:22.11,3,IIP,Yes,No,Yes,175b15d9
178,00:01:22.14,9,IPBBPBBPB,Yes,No,Yes,17625d8e
179,00:01:22.23,9,IBBPBBPBB,No,No,Yes,1777f8bb
180,00:01:23.02,12,IPBBPBBPBBPB,Yes,No,Yes,178d9f40
181,00:01:23.14,5,IPBBP,Yes,No,Yes,17aa8fca
182,00:01:23.19,3,IPB,Yes,No,Yes,17b6a9af
183,00:01:23.22,11,IPBBPBBPBBP,Yes,No,Yes,17bdf5e2
184,00:01:24.03,15,IIIIIIPIIPBIIII,Yes,No,Yes,17d87815
185,00:01:24.18,2,II,Yes,No,Yes,17fcb067
186,00:01:24.20,6,IPBBPB,Yes,No,Yes,18018f7f
187,00:01:24.26,5,IPBIP,Yes,No,Yes,181010dc
188,00:01:25.01,10,IPBBPBBPBB,Yes,No,Yes,181c2fcc
189,00:01:25.11,1,I,Yes,No,Yes,18344ecc
190,00:01:25.12,4,IPBB,Yes,No,Yes,1836d23a
191,00:01:25.16,6,IPIIII,Yes,No,Yes,18407d17
192,00:01:25.22,4,IPBB,Yes,No,Yes,184ef3af
193,00:01:25.26,12,IPBBPBBPBBPB,Yes,No,Yes,18589f2c
194,00:01:26.08,5,IIIIP,Yes,No,Yes,1875984c
195,00:01:26.13,6,IPBBPB,Yes,No,Yes,1881c688
196,00:01:26.19,4,IPII,Yes,No,Yes,1890455a
197,00:01:26.23,13,IPBBPBBPBBPBB,Yes,No,Yes,1899e722
198,00:01:27.06,5,IIIII,Yes,No,Yes,18b94a89
199,00:01:27.11,15,IPBBPBBPBBPBBPB,Yes,No,Yes,18c55b14
200,00:01:27.26,15,IBBPBBPBBPBBPBB,No,No,Yes,18e999a2
201,00:01:28.11,15,IBBPBBPBBPBBPBB,No,No,Yes,190dde5c
202,00:01:28.26,15,IBBPBBPBBPBBPBB,No,No,Yes,19322063
203,00:01:29.11,15,IBBPBBPBBPBBPBB,No,No,Yes,19566479
204,00:01:29.26,15,IBBPBBPBBPBBPBB,No,No,Yes,197aacf5
205,00:01:30.11,15,IBBPBBPBBPBBPBB,No,No,Yes,199ef42e
206,00:01:30.26,15,IBBPBBPBBPBBPBB,No,No,Yes,19c33b5a
207,00:01:31.11,15,IBBPBBPBBPBBPBB,No,No,Yes,19e7821e
208,00:01:31.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1a0bb543
209,00:01:32.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1a2ffbb5
210,00:01:32.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1a54538f
211,00:01:33.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1a78a328
212,00:01:33.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1a9ce559
213,00:01:34.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1ac12c88
214,00:01:34.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1ae571df
215,00:01:35.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1b09b790
216,00:01:35.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1b2e7f82
217,00:01:36.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1b52a677
218,00:01:36.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1b76d4ed
219,00:01:37.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1b9b06e3
220,00:01:37.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1bbf3e93
221,00:01:38.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1be37900
222,00:01:38.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1c07b69b
223,00:01:39.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1c2bf7dc
224,00:01:39.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1c50397d
225,00:01:40.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1c747aa1
226,00:01:40.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1c98c2db
227,00:01:41.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1cbd0799
228,00:01:41.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1ce15654
229,00:01:42.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1d05a8bc
230,00:01:42.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1d29eb7a
231,00:01:43.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1d4e2dd9
232,00:01:43.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1d727768
233,00:01:44.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1d96b932
234,00:01:44.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1dbaf76b
235,00:01:45.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1ddf4669
236,00:01:45.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1e038bb6
237,00:01:46.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1e27d2d3
238,00:01:46.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1e4c11c9
239,00:01:47.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1e730ffa
240,00:01:47.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1e96abfb
241,00:01:48.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1eba6d6b
242,00:01:48.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1ede5800
243,00:01:49.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1f0252b6
244,00:01:49.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1f266082
245,00:01:50.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1f4b3e28
246,00:01:50.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1f6f4013
247,00:01:51.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1f934ac5
248,00:01:51.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1fb765bf
249,00:01:52.11,15,IBBPBBPBBPBBPBB,No,No,Yes,1fdb8d6d
250,00:01:52.26,15,IBBPBBPBBPBBPBB,No,No,Yes,1fffc15b
251,00:01:53.11,15,IBBPBBPBBPBBPBB,No,No,Yes,2023f1bd
252,00:01:53.26,15,IBBPBBPBBPBBPBB,No,No,Yes,20482fa5
253,00:01:54.11,15,IBBPBBPBBPBBPBB,No,No,Yes,206c6a45
254,00:01:54.26,15,IBBPBBPBBPBBPBB,No,No,Yes,2090ac6b
255,00:01:55.11,15,IBBPBBPBBPBBPBB,No,No,Yes,20b4e9bb
256,00:01:55.26,14,IBBPBBPBBPBBPB,No,No,Yes,20d92dc3
257,00:01:56.10,14,IBBPBBPBBPBBPB,No,No,Yes,20fb01d5
258,00:01:56.24,15,IPBBPBBPBBPBBPB,Yes,No,Yes,211cd509
259,00:01:57.09,15,IBBPBBPBBPBBPBB,No,No,Yes,21411bc3
260,00:01:57.24,15,IBBPBBPBBPBBPBB,No,No,Yes,21656231
261,00:01:58.09,15,IBBPBBPBBPBBPBB,No,No,Yes,2189a8b2
262,00:01:58.24,15,IBBPBBPBBPBBPBB,No,No,Yes,21adf2b2
263,00:01:59.09,15,IBBPBBPBBPBBPBB,No,No,Yes,21d23aa9
264,00:01:59.24,15,IBBPBBPBBPBBPBB,No,No,Yes,21f68020
265,00:02:00.09,15,IBBPBBPBBPBBPBB,No,No,Yes,221ac8b7
266,00:02:00.24,15,IBBPBBPBBPBBPBB,No,No,Yes,223f0e63
267,00:02:01.09,14,IBBPBBPBBPBBPB,No,No,Yes,226356cf
268,00:02:01.23,14,IBBPBBPBBPBBPB,No,No,Yes,22853217
269,00:02:02.07,15,IPBBPBBPBBPBBPB,Yes,No,Yes,22a70bfd
270,00:02:02.22,15,IBBPBBPBBPBBPBB,No,No,Yes,22cb5235
271,00:02:03.07,15,IBBPBBPBBPBBPBB,No,No,Yes,22ef9d84
272,00:02:03.22,15,IBBPBBPBBPBBPBB,No,No,Yes,2313de2e
273,00:02:04.07,15,IBBPBBPBBPBBPBB,No,No,Yes,23382ee4
274,00:02:04.22,15,IBBPBBPBBPBBPBB,No,No,Yes,235c6d81

[xtreemkareem]

-/+ R is obviously best!

[BJ_M]

if you notice also -- i have the IPB pattern change through out depending on the scene changes

[J3M]

Now that was an explaination I could understand Lordsmurf. Thanks!

I'm going to try adjusting my GOP settings in ATI MMC this weekend and see what I get. So the 2 and 2 is less compression, while 4 and 2 and up is higher compression. Correct?

BTW, by the sounds of it, I guess I'm glad I have been using 2 and 2, since the primary show I've been capturing on a regular basis has been Family Guy.

Thanks to everyone for your replies!

[DVDDave]

Neither, Dave. Everybody knows VCD is kind and DVD is shite.

I was kidding!!!