Is the Drop-Frame flag always constant across all GOPs?

kumi · 23rd November 2005, 02:41

When I flag a MPEG2 stream as drop-frame in pulldown.exe, it looks like all the GOP Video Packs' DF bits are set to 1. Likewise when I set to non-drop: all DF bits are set to 0.

Is it in the DVD-Video specifications that an MPEG2 stream must have drop-frame flag bits set to ALL 0 or ALL 1? i.e. no mixing of non-drop frame and drop frame between GOPs.

mpucoder · 23rd November 2005, 03:26

Quote:

Originally Posted by kumi

When I flag a MPEG2 stream as drop-frame in pulldown.exe, it looks like all the GOP Video Packs' DF bits are set to 1. Likewise when I set to non-drop: all DF bits are set to 0.

That's just the way the program works - any changes are applied to all occurences.

Quote:

Is it in the DVD-Video specifications that an MPEG2 stream must have drop-frame flag bits set to ALL 0 or ALL 1? i.e. no mixing of non-drop frame and drop frame between GOPs.

DVD-Video doesn't care at all about any information in the GOP header. Most authoring programs read only the first timecode, if any, in a video elementary stream. However, mixing the flag values within a segment is not allowed according to the mpeg specifications, and would make no sense as the flag affects the interpretation of the timecode.

kumi · 23rd November 2005, 05:25

Thanks mpucoder. I ask because I want a quick and easy way to find out if I need to set drop-frame for custom subtitles. So, am I right in assuming that if any GOP is set to drop-frame, I can safely set my subtitle authoring program to output drop-frame?

EDIT: nevermind.. I re-read your post, and the answer is yes

23rd November 2005, 02:41	#1 \| Link
kumi Straight to video Join Date: Jun 2005 Posts: 637	Is the Drop-Frame flag always constant across all GOPs? When I flag a MPEG2 stream as drop-frame in pulldown.exe, it looks like all the GOP Video Packs' DF bits are set to 1. Likewise when I set to non-drop: all DF bits are set to 0. Is it in the DVD-Video specifications that an MPEG2 stream must have drop-frame flag bits set to ALL 0 or ALL 1? i.e. no mixing of non-drop frame and drop frame between GOPs.

23rd November 2005, 05:25	#3 \| Link
kumi Straight to video Join Date: Jun 2005 Posts: 637	Thanks mpucoder. I ask because I want a quick and easy way to find out if I need to set drop-frame for custom subtitles. So, am I right in assuming that if any GOP is set to drop-frame, I can safely set my subtitle authoring program to output drop-frame? EDIT: nevermind.. I re-read your post, and the answer is yes Last edited by kumi; 23rd November 2005 at 07:48.