[Octave-bug-tracker] [bug #35191] aviread does not obey video time scale

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?35191>

                 Summary: aviread does not obey video time scale
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Thu 29 Dec 2011 04:59:05 PM UTC
                Category: Libraries
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Inaccurate Result
                  Status: None
             Assigned to: None
         Originator Name: Grieviant
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.2.4
        Operating System: Microsoft Windows

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Details:

I'm encountering a problem using aviread() to extract video frames from an
h264 encoded .mp4 file.  aviinfo() gives

Filename = C:\Temp\GH1.MP4
FileSize =  11853799
FileModDate = 19-Dec-2011 11:14:06
NumFrames =  32
FramesPerSecond =  59.940
Width =  1280
Height =  720
ImageType = truecolor
VideoCompression = h264
Quality =  100
NumColormapEntries = 0
AudioFormat = aac
AudioRate =  48000
NumAudioChannels =  2

This all looks correct except for the NumFrames parameter.  The video is 18
seconds in length and therefore has about 18*60 = 1080 frames (file size =
11.3 MB).  Is aviinfo() maybe returning the number of key frames rather than
the total number of frames?

Anyway, on to the problem.  When I read and display the first 5 frames with
aviread(), what I see is the 1st frame repeated 4 times, followed by the 5th
frame.  It's as if aviread() is doing a coarse decimation rather than
interpolating at the correct points in time.  This happens regardless of what
frame offset into the video stream I choose, not just at the start.


% Get video info
vinfo = aviinfo([dname,fname]);
vinfo

% Read and display a few frames
Nframes = 5;
Vc = cell(1,Nframes);
xframe = 1;

for(i=1:Nframes)
   v = aviread([dname,fname], xframe+i-1);
   Vc{i} = v;
end

for(i=1:Nframes)
   figure;
   axis equal;
   image(Vc{i});
end


I should also mention that both QuickTime and VLC yield the correct results
when scrolling this video frame by frame.  I've heard that VLC also uses
ffmpeg, so it would seem that the bug is unique to aviread() rather than a
problem with ffmpeg.

If it's really necessary I could post the images which show the results I'm
getting, but hopefully this description is good enough.

Octave 3.2.4 on Win7 64
video-1.0.2 package
    




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