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• Random access to video frame by its id

  22 août 2018, par Xmiler

  I have a 24 hour video and would like to organize storage of some meta information (particularly bounding boxes of objects) for arbitrary frame. It implies that I must have a reliable random access to frame by its id, practically even to the range of frames in a way (id_start, id_end).

  Once again, it is critically to get the same frame when I fill meta storage and when I will get meta later (in general in another environment - ffmpeg version, codecs etc). Otherwise I will put bounding box on the wrong frame.

  So there ways I found

  1. ffmpeg -i in.mp4 -vf select='between(n,x,y)' -vsync 0 frames%d.png
     The problem is it works too slow. Also I don’t know is it reliable in sense of reproducing.

  2. ffmpeg -ss pkt_pts_time -i in.mp4 -vframes n output_%03d.png
     where pkt_pts_time got from ffprobe -show_frames in.mp4 -select_streams v
     The problem is pkt_pts_time not clear at all. Does pkt_pts_time refer to -ss parameter ?

  Actually the question is - does internal meta information of frame (say h.264) contain frame id ? I didn’t find way to get it.

  Now I am thinkig to store png md5sum for each T’s frame (anchor). Later I will be able to check consistency using them.

  Can anyone suggest something better ?

• OS X Mavericks broken OpenCV VideoCapture frame numbers ?

  20 novembre 2013, par MattP

  Fresh install of Mavericks, managed to install ffmpeg via homebrew and compile the latest OpenCV at time of writing. My code is written in Python (though this shouldn't affect this issue) and basically navigates a video file using the VideoCapture class with the properties set frame position and get current position.

  The issue is, on prior versions of OS X, various Linux and Windows boxes, this works without issue. Each frame number is of the format i.0, where i is the current frame number (why it is a float anyway is confusing, alas it's how OpenCV gives it back). However, on this setup I get frame progressions like :

  0.0 -> 1.3972597329753 -> 2.999999999 -> 3.9999999 -> 5.0 -> 6.252323552

  This makes using the properties for getting / setting the current frame position impossible and, as one would imagine, causes the automated playback thereof to fail. I can only assume ffmpeg is reporting things odd such that OpenCV is incorrectly calculating frames, but have been unable to rectify this.

  Has anyone any insight into the problem, and/or possible solution ? Thanks.

• Anomalie #3183 : les liens issus de la syndication sont invalides

  1er avril 2014, par b b

  Je confirme le bug sur grml.eu en syndiquant le flux suivant :

  http://www.eco-sol-brest.net/spip.php?page=backend&id_mot=70

  Les liens contenus dans les items du flux sont tous modifiés pour devenir de la forme :

  http://sitesource.bb/%22http:/autresite.bb/article3373.html%22

  Tout ceci est visible par ici :

  http://b_b.grml.eu/spip.php?site1

  La syndication est bien cassée :