Author Topic: Cutting Video off I-frames without re-encoding  (Read 2126 times)

EEMcGee

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Cutting Video off I-frames without re-encoding
« on: May 04, 2016, 05:11:59 AM »
When editing videos without re-encoding, your "A point" (beginning of the segment) does not have to be on an I-frame.  Only the "B point" has to be on an I-frame.I was cutting commercials out of some TV shows I have recorded.  the problem is the I-frames don't always come until after the commercial has started.  So if you go to the first I-frame in the commercial then step back a frame at a time you can make sure to cut any of the commercial that was in the P or B-frames from the last I-frame.  You can not do the same on the "B point" end since you would be leaving P or B frames without an I-frame to reference.

AQUAR

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Re: Cutting Video off I-frames without re-encoding
« Reply #1 on: May 04, 2016, 01:28:07 PM »
No expert myself.
But if the "A point" is on say a B frame and that B frame requires information from a future frame (as in the commercial) than would it not become orphan.

As that not a possibility with modern codecs?

EEMcGee

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Re: Cutting Video off I-frames without re-encoding
« Reply #2 on: May 04, 2016, 11:30:47 PM »
No.   I may be wrong but I don't think a B-frame will reference frames that come after it.  I have been doing it on MPeg2 videos without any problem.  Somebody please correct me if there are any codecs (maybe Mpeg4) that would do this.  It could be that referencing future frames is possible on some codecs but not standard practice on broadcast or DVD/Bluray video as a matter of compatibility.
« Last Edit: May 04, 2016, 11:39:18 PM by EEMcGee »

Jan Gruuthuse

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Re: Cutting Video off I-frames without re-encoding
« Reply #3 on: May 05, 2016, 05:06:15 AM »
On some codecs this works on others not. (When re-encoding this becomes is less important.)
When editing with copy for both video and audio output, I would not recommend cutting on none I-frames.
The newer codecs require information from previous and future image blocks to rebuild some part of a current shown image.