CvCapture_FFMPEG::setProperty( int property_id, double value )
is incorrect.

1. it give it wrong parameters
2. av_seek_frame return only key frames, and so you can not use setProperty function to set the capture to a non-key frame.

FIX:¶

i written a function that seek for the nearest key frame and from there it grab frames until it reach the desired frame.

 1#DEFINE SHORTER_DISTANCE_FOR_SEEK_TO_MAKE_IT_FASTER
 2bool seekKeyAndRunOverFrames(int framenumber) 
 3{
 4  int ret;
 5  if (framenumber > video_st->cur_dts-1)
 6  {
 7     if (framenumber-(video_st->cur_dts-1) >  SHORTER_DISTANCE_FOR_SEEK_TO_MAKE_IT_FASTER) {
 8       ret=av_seek_frame(ic, video_stream, framenumber, 1); 
 9       assert(ret>=0);
10       if(ret<0)
11      return false;
12     }
13     grabFrame();
14     while ((video_st->cur_dts-1) < framenumber)
15        if ( !grabFrame() ) return false;
16  }
17  else if ( framenumber < (video_st->cur_dts-1) )
18  {
19     ret=av_seek_frame(ic, video_stream, framenumber, 1); 
20     assert(ret>=0);
21     if(ret<0)
22    return false;
23     grabFrame();
24     while ((video_st->cur_dts-1) < framenumber )
25        if ( !grabFrame() ) return false;
26   }
27   return(true);
28}

and it is called by setProperty:

 1bool CvCapture_FFMPEG::setProperty( int property_id, double value )
 2{
 3    if( !video_st ) return false;
 4    int ret;
 5    int framenumber;     
 6    AVRational time_base;
 7    switch( property_id )
 8       {
 9        case CV_CAP_PROP_POS_FRAMES:
10            framenumber=(int)value;
11            return seekKeyAndRunOverFrames(framenumber);
12            break;
13
14        case CV_CAP_PROP_POS_MSEC:
15            framenumber=value/(1000.0f * av_q2d (video_st->time_base));
16            return seekKeyAndRunOverFrames(framenumber);
17            break;
18
19        default:
20            return false;
21    }
22
23    return false;
24}

CV_CAP_PROP_POS_RATIO should throw an "not implemented" exception as for many captures we can not get the correct number of frames per stream.