src/main/java/org/jcodec/api/FrameGrab.java
public static Picture getNativeFrameSloppy(SeekableDemuxerTrack vt, ContainerAdaptor decoder, int frameNumber)
            throws IOException, JCodecException {
        return new FrameGrab(vt, decoder).seekToFrameSloppy(frameNumber).getNativeFrame();
    }
public static Picture getNativeFrameSloppy(SeekableDemuxerTrack vt, ContainerAdaptor decoder, int frameNumber)
            throws IOException, JCodecException {
        return new FrameGrab(vt, decoder).seekToFrameSloppy(frameNumber).getNativeFrame();
    }
Get a specified frame by number from an already open demuxer track (
sloppy mode, i.e. nearest keyframe )

@param vt
@param decoder
@param frameNumber
@return
@throws IOException
@throws JCodecException