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View Full Version : strange timing issues demuxing with pgcDemux


maman
26th May 2011, 23:28
I've been trying to investigate some weird thumbnail creation issues in multiAVCHD, and I think i've traced it back to this...

I ripped/demuxed a home dvd (i.e. no encryption or other protection) using pgcDemux. The file is about 1hr 20 min long. The resulting file ripped and plays back fine. But I noticed that the run time that shows up when I click on the file is about 50 min.

I also transcoded this file with multiAVCHD and the resulting output video shows correctly as 1hr 20 min. Through some experimentation, i've found that when I play the files side by side, the running timers and video are in sync. BUT, if I were to open the pgcDemux output file and /skip/ to a certain point in the movie, time timestamp for that part is completely different than what it would have been if I had just let the video play naturally to that part...

So, a frame that normally comes up around 10 min if I let the file play naturally, will also come up if I open the file and move the playhead to 6:30.

Since you seek through the file to chose chapters and set thumbnails in multiAVCHD, this produces some completely unexpected results between what you see when you set the thumbs, and what thumbs you actually get when you publish, since the timecodes point to a totally different place.

It seems like the issue is the way pgcDemux is demuxing my dvd... does anyone know what my issue might be here? Originally I thought it might be a framerate issue, but it seems like the framerate is being read correctly (especially since multiAVCHD is picking up/transcoding with the same framerate and the resulting file shows as being the correct length)

Groucho2004
26th May 2011, 23:36
Nothing strange about it. A raw MPEG-2 stream (m2v) has to be parsed/indexed in order to retrieve the number of frames. When you open that stream in a media player it does not know the number of frames.

maman
27th May 2011, 00:13
thanks for the reply. Sorry, I'm a bit of a noob about this stuff, can you elaborate?

Where is it getting this value of the length of 52 min? And it seems skipping to a specific point in the movie regardless of the software being used results in a consistent (though incorrect) time code.

Is there any way I can get around this? I'd like to be able to set my chapter thumbnails correctly through the multiAVCHD interface.

Groucho2004
27th May 2011, 00:44
Where is it getting this value of the length of 52 min?

No idea, probably random.

Multiplex the stream to VOB with Muxman. multiAVCHD should be able to read that.

maman
27th May 2011, 04:23
dude...

I didn't realize I could just load the vob files directly! Actually I load the IFO and it even keeps all the chapter info for me. This removes several extra steps AND eliminates my problem. Thanks!