How many frames in a 25 fps GOP ?

MarcioAB · 1st July 2006, 22:13

Hello,

In basic 30 fps NTSC video, each GOP (group of pictures) in general has 15 frames / ( 0.5 second * 1.001 )

In movie 24 fps NTSC video, each GOP has 12 frames / ( 0.5 second * 1.001 ).

Could someone inform how are those numbers for PAL ( 25 fps ) ?

Thank you
Marcio

unskinnyboy · 1st July 2006, 22:29

For PAL -> 15.

P.S: For NTSC, it's not 15, but 18.

MarcioAB · 2nd July 2006, 00:12

Hum .. using VobEdit on a NTSC video just created here using a DVD Recorder I can see:

15 frames in each GOP ( IBBPBBPBBPBBPPP ).
45045 ticks between the PTS of 2 consecutives GOPs

Using VobEdit on a NTSC video from the film "The Chronicles of Riddick" I can see:

12 frames in each GOP ( IBBPBBPBBPBB ).
45045 ticks between the PTS of 2 consecutives GOPs

I do not have any PAL video here to check directly with VobEdit how their GOPs are structured in terms of frames and PTS.

You say PAL GOP = 15 frames and NTSC GOP = 18 frames. Then the PTS delta should be 54000 ticks (or 0.6 seconds).

So, over here I'm getting PTS deltas of 0.5 seconds and you 0.6 seconds.

Interesting ... is that the correct thinking direction ?

Thank you
Marcio

unskinnyboy · 2nd July 2006, 00:39

18 is the maximum allowed. So if you see a 15 frame GOP, that's fine. As for the PTS deltas, as per specs it should be >= 0.4s and <= 1.0s (except for the last VOBU, which can be <= 1.2s), so 0.5s and 0.6s are fine too.

MarcioAB · 2nd July 2006, 03:56

thank you.

1st July 2006, 22:13	#1 \| Link
MarcioAB Registered User Join Date: Nov 2005 Posts: 153	How many frames in a 25 fps GOP ? Hello, In basic 30 fps NTSC video, each GOP (group of pictures) in general has 15 frames / ( 0.5 second * 1.001 ) In movie 24 fps NTSC video, each GOP has 12 frames / ( 0.5 second * 1.001 ). Could someone inform how are those numbers for PAL ( 25 fps ) ? Thank you Marcio

1st July 2006, 22:29	#2 \| Link
unskinnyboy Registered User Join Date: Feb 2004 Location: NTSC R1 Posts: 2,054	For PAL -> 15. P.S: For NTSC, it's not 15, but 18. __________________ I encode, therefore I am. Doom9 Toolbar Extension for Firefox [v3.1]

2nd July 2006, 00:39	#4 \| Link
unskinnyboy Registered User Join Date: Feb 2004 Location: NTSC R1 Posts: 2,054	18 is the maximum allowed. So if you see a 15 frame GOP, that's fine. As for the PTS deltas, as per specs it should be >= 0.4s and <= 1.0s (except for the last VOBU, which can be <= 1.2s), so 0.5s and 0.6s are fine too. __________________ I encode, therefore I am. Doom9 Toolbar Extension for Firefox [v3.1]

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2nd July 2006, 00:12	#3 \| Link
MarcioAB Registered User Join Date: Nov 2005 Posts: 153	Hum .. using VobEdit on a NTSC video just created here using a DVD Recorder I can see: 15 frames in each GOP ( IBBPBBPBBPBBPPP ). 45045 ticks between the PTS of 2 consecutives GOPs Using VobEdit on a NTSC video from the film "The Chronicles of Riddick" I can see: 12 frames in each GOP ( IBBPBBPBBPBB ). 45045 ticks between the PTS of 2 consecutives GOPs I do not have any PAL video here to check directly with VobEdit how their GOPs are structured in terms of frames and PTS. You say PAL GOP = 15 frames and NTSC GOP = 18 frames. Then the PTS delta should be 54000 ticks (or 0.6 seconds). So, over here I'm getting PTS deltas of 0.5 seconds and you 0.6 seconds. Interesting ... is that the correct thinking direction ? Thank you Marcio

2nd July 2006, 03:56	#5 \| Link
MarcioAB Registered User Join Date: Nov 2005 Posts: 153	thank you.