Position Seek setting ignored?

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glenviewjeff
Posts: 2
Joined: Thu Aug 13, 2015 9:18 pm

Position Seek setting ignored?

Post by glenviewjeff »

I'm trying to thumbnail a big folder of mp4 files. The position seek doesn't seem to be having any effect, whether I start it at the beginning, middle, or end position. I disabled the luminance and entropy setting, as well as the "enable cover art display" as a troubleshooting step, and of course am dragging files over to the testing and cache tab to see the results. Of course I'm also hitting the "apply" button after making setting changes.

It seems that whatever position-seek setting I choose, the thumbnail is generated with the frame at the beginning of the file. Is this a limitation with mp4 files or something?
BabelSoft
Site Admin
Posts: 342
Joined: Sat Jun 02, 2012 9:23 pm

Re: Position Seek setting ignored?

Post by BabelSoft »

There are some video files that have been encoded without any key frames. With this kind of files, it's impossible to do a fast position seek, you have to decode every frame since the very first one until your target frame to get the wanted thumbnail. So depending on the total video sequence length, the requested position and your computer performances, it could take a very long time to get anything (sometimes as long as actually watching the video sequence itself...). So when Media Preview detects this kind of files, it simply ignores the configured seeking position and remains at the beginning.

It doesn't have to do with the file format (mp4 or mkv) but only with the way it has been encoded. You can send me some samples so I can confirm if we're really dealing with files missing key frames or if it's a bug. But I really think that this is rather the former than the later.
glenviewjeff
Posts: 2
Joined: Thu Aug 13, 2015 9:18 pm

Re: Position Seek setting ignored?

Post by glenviewjeff »

Yes, I wouldn't be at all surprised if key frames aren't present. These are taken from a video motion detection phone app. I'm really just looking for a quick way to scan through lots of motion detected files to see if there's anything of interest, but the video files include pre-motion detected segments so that you're sure to capture the whole event. It would be really nice if there were a "process whole file intensively" option that warned of slow performance.

What I honestly need is a tool for displaying a handful of stills of each video so I can visually scan for interesting events without watching all the footage. I'm sure there's a video editor out there somewhere that will do it, but I have zero budget for it. :)

Thanks!
Jeff
BabelSoft
Site Admin
Posts: 342
Joined: Sat Jun 02, 2012 9:23 pm

Re: Position Seek setting ignored?

Post by BabelSoft »

It's not really an option that would be useful for a lot of people...
But alternatively, you can re-encode those files, e.g. with Handbrake, to insert proper key frames. The default mp4 encoding options should be good enough to do the trick for Media Preview.
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