[FFmpeg-user] frame extract is not accurate enough

Luk√°csy Gergely Gergely.Lukacsy at streamnet.hu
Mon Jul 27 17:46:48 CEST 2015


> Smaller, you meant to say? Actually, you mistyped 496?

Damn... yes, I mistyped it, the correct duration is 296 (as you noticed in the console log).

> Perhaps  that's according to the header, and the actual video stream is longer,
resulting in about 300 seconds.

I think ffmpeg never outputs the header information regarding duration and such.
Running an empty run with ffmpeg shows me that the video is composed of 7423 frames which translates to exactly 296.92 seconds if we calulate with 25 fps ( 7423 / 25 = 296.92 ).

> Are you sure the video is truly CFR? Is it captured from some device
which delivers slightly varying frame rate?

You can never be 100% sure about that, but I think this video has constant frame rate (see the results above). :)
We captured a notebook screen with an Epiphan Pearl, which may alter the frame rate in certain conditions, but in this case the CPU was far away from overload.

Cheers,
Gergely.



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