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CutlistEditor - missing audio?

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#1 heksesang

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Posted 13 July 2013 - 22:39

So, today I recorded an episode of Friends and made an attempt to add a cutlist to remove commercials using Comskip. I found the start and end PTS values for each part that was not commerical and added them along with type (0 for start and 1 for end) in the .cuts file. When I then play it or execute the cuts with MovieCut, it plays without the commercials.

 

What bothers me is that for some reason, the audio cuts out for 1-2 seconds at the in and out marks. Meaning I lose whatever is said during those seconds. How do I fix that?



Re: CutlistEditor - missing audio? #2 Erik Slagter

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Posted 14 July 2013 - 08:44

Comskip? I don't think that's in our feeds.

 

You will never to be able to cut a exact points because this way you can only cut at GOP-boundaries, for cutting at frame level, you'll need to recode.

 

Also, as the audio and video streams need not be in the exact same position in the stream (fysically, byte offsets), it's quite normal to loose some audio or subtitles etc.


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Re: CutlistEditor - missing audio? #3 heksesang

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Posted 14 July 2013 - 12:30

Comskip? I don't think that's in our feeds.

 

You will never to be able to cut a exact points because this way you can only cut at GOP-boundaries, for cutting at frame level, you'll need to recode.

 

Also, as the audio and video streams need not be in the exact same position in the stream (fysically, byte offsets), it's quite normal to loose some audio or subtitles etc.

Comskip is just the application I use to find the frames. And as I said, I translate the frame numbers to PTS values, which should be synchronized with all the elementary streams in the transport stream.

Would cutting at GOP boundaries fix the audio skip?



Re: CutlistEditor - missing audio? #4 heksesang

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Posted 14 July 2013 - 12:58

And is there a list of GOP boundaries in one of the files? Or do I have to look up that from the TS file?



Re: CutlistEditor - missing audio? #5 MiLo

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Posted 14 July 2013 - 17:59

The .ap file contains a list of offset/timestamp values (in 64-bit big endian).


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Re: CutlistEditor - missing audio? #6 heksesang

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Posted 14 July 2013 - 23:49

The .ap file contains a list of offset/timestamp values (in 64-bit big endian).

Alright, so then the flow is to identify frames with Comskip, translate frames into zero-based PTS values, add that to first PTS value from .ap files (those are absolute, so using the first as a point of zero), then find the closest PTS value in the .ap file (floor for start, ceil for end).



Re: CutlistEditor - missing audio? #7 Erik Slagter

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Posted 15 July 2013 - 09:22

Comskip is just the application I use to find the frames. And as I said, I translate the frame numbers to PTS values, which should be synchronized with all the elementary streams in the transport stream.

Would cutting at GOP boundaries fix the audio skip?

No, GOP = video only. The only reliable way to fix this, without re-encoding, would be an approach like ProjectX does (for mpeg2): demux the streams, but keep the timestamps, then remux while repeating/dropping audio frames so PES packets with equal PTS (either explicit or implicit) from different streams are always next to each other. After that, you can cut at GOP boundaries and always have the audio correctly.

 

Another approach would be an editor that deals with streams and timestamps in a transport stream in an intelligent way, but the cutlist editor / movie cutter definitely don't work as such.

 

Simplest approach is to re-encode to an intra-only codec (like mjpeg) cut that and re-encode to h264 (once more)  ;)


* Wavefrontier T90 with 28E/23E/19E/13E via SCR switches 2 x 2 x 6 user bands
I don't read PM -> if you have something to ask or to report, do it in the forum so others can benefit. I don't take freelance jobs.
Ik lees geen PM -> als je iets te vragen of te melden hebt, doe het op het forum, zodat anderen er ook wat aan hebben.




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