[mpeg2] Re: KFir MPEG2 editing

[MAL <mal@komcept.com>]

So you're basically removing data from the stream to smoothen it out... ?
If that's the case, is it noticable?  I ask because this is for an 
interview recorder, and it's pretty important that nothing is missed.
I'd think about using GOPchop if it had a command line interface :)

Sorry, I can't release the code as it's part of a commercial project.

Regards,
MAL

Kees Cook wrote:

>GOPchop will do this for you.  I designed it using kfir streams, so I 
>think most of the bugs are worked out.  Check:
>
>gopchop.sourceforge.net
>
>
>I haven't found a single decoder that actually pays attention to the 
>"broken_link" flag.  I find this _highly_ irritating.  Since GOPs are 
>optional headers, I assume that these decoders are just cutting corners 
>and ignoring the GOPs.  To solve this problem in GOPchop, I would do two 
>things: the "correct" thing, which is setting the "broken_link" flag, and 
>then I actively remove all the B-frames from the video stream that follow 
>the first I-frame.  This appears to totally do the trick.  I also set the 
>"closed" bit, since now the GOP is closed.
>
>Can you share your code with us?  In my most recent CVS, I wrote "mpegcat" 
>which will spit out all kinds of information about an MPEG2-PS file, 
>reporting locations, sizes, and flags of all the headers.
>
>On Wed, Feb 06, 2002 at 02:12:21PM +0000, MAL wrote:
>
>>This is a last call for aid...
>>I am trying to cut sections from an MPEG2 generated by a KFir.
>>By my understanding, the KFir uses bi-directional frame coding (IBP), as 
>>opposed to progressive frame coding, which makes cutting the files at 
>>clean boundaries very hard.
>>I need to be able to cut a file into sections, (for burning to cd 
>>progressively), and those sections need to be sequential without loss.
>>
>>I have written a program to almost completely dissect an MPEG2, 
>>(everything bar decoding the actual pictures), and output a section, but 
>>regardless of whether I set the group of pictures' header's 
>>'broken_link' flag, I still get corrupt starts to the beginning of my 
>>sections.  The closed_gop flag within the mpeg2 is set, meaning the fkir 
>>doesn't encode cleanly cuttable group_of_pictures.
>>
>>Does anyone know of a way I can "fix" the mpeg2 to have cleanly cuttable 
>>boundaries, or will I need to re-encode the whole file?
>>
>>_Any_ help on this subject would be great, I refuse to believe there is 
>>no way to do it :)
>>
>>Also, if anyone knows whether you can get the KFir to encode 
>>differently, shout me pls.
>>
>>All the best,
>>
>>MAL
>>Komcept Solutions Ltd.
>>United Kingdom
>>
>