Hi there,

This is a very technical question that I fully expect to go unanswered but I am gonna give it a shot since it is driving me nuts. I hope this is the right forum - mods please move if not.

Q: How does the AVC stream handle 23.976 fps progressive frame encoding with pulldown hint flags to give 29.97 fps interlaced output?

Obviously it has to be able to do this in order to encode HD DVDs, but I can't for the life of me find any reference to this obviously common practice in the ITU spec or anywhere else for that matter.

If anyone has any pointers, please let me know...

what do you want to do? add a pulldown to a 23.976fps hd-dvd complaint avc stream for authoring?

That sort of thing.

I mainly want to understand the mechanism, what flags need to be set, etc.

I think AVC is really interesting but the ITU spec is one of the most difficult to follow tech documents I have ever read. It makes the MPEG2 docs seem like light reading :D

Hi there,

This is a very technical question that I fully expect to go unanswered but I am gonna give it a shot since it is driving me nuts. I hope this is the right forum - mods please move if not.

Q: How does the AVC stream handle 23.976 fps progressive frame encoding with pulldown hint flags to give 29.97 fps interlaced output?

Obviously it has to be able to do this in order to encode HD DVDs, but I can't for the life of me find any reference to this obviously common practice in the ITU spec or anywhere else for that matter.

If anyone has any pointers, please let me know...
It's done in the Picture timing SEI message. See table D-1, interpretation of pic_struct in the specification.

Ron

Excellent, thanks so much for that.

Saved me a lot of searching the spec.

Excellent, thanks so much for that.

Saved me a lot of searching the spec.
Here's a tool for you to dump the pic_struct flags. It's from the MPEG4IP package found here:

http://mpeg4ip.sourceforge.net/documentation/index.php

I've made a .zip file with the compiled executable and just the required source files. I've also made some bug fixes to make it work for high bitrate HDM bitstreams and AVCHD bitstreams.

http://www.w6rz.net/h264_parse.zip

Ron

Heh, great, thanks.

A semi related follow up question...

If one was to change the timing ratio in the Sequence Parameter Set, is there some kind of time code information that would become incorrect as a result?

For example, a European broadcast of a film might be at 25 fps, and if you change the ratio to make it 23.976, some applications report the run length as being now 25/23.976 longer than before, implying that there is some time code or similar data in some streams that is based on the timing ratio...?

Once again pointers appreciated. Thanks in advance.