public static Pipeline BuildVideoReaderPipelineCustom()
        {
            // Build video reader pipeline

            var fileSrc = ElementFactory.Make("filesrc", "filesrc");
            if (fileSrc == null)
            {
                throw new ArgumentNullException(nameof(fileSrc));
            }
            
            var qtdemux = ElementFactory.Make("qtdemux", "qtdemux");
            if (qtdemux == null)
            {
                throw new ArgumentNullException(nameof(qtdemux));
            }


            var queue = ElementFactory.Make("queue", "queue");
            if (queue == null)
            {
                throw new ArgumentNullException(nameof(queue));
            }

            var h264parse = ElementFactory.Make("h264parse", "h264parse");
            if (h264parse == null)
            {
                throw new ArgumentNullException(nameof(h264parse));
            }

            var avdec = ElementFactory.Make("avdec_h264", "avdec_h264");
            if (avdec == null)
            {
                throw new ArgumentNullException(nameof(avdec));
            }


            var appSink = new AppSink("my_appsink");
            //appSink.NewSample += AppSink_NewSample;
            // appSink.EmitSignals = true;
            appSink["sync"] = true;

            h264parse.PadAdded += (o, args) =>
            {
                //args.Args[0] as 
                var appsinkPad = appSink.GetStaticPad("sink");

                if (appsinkPad.IsLinked)
                {
                    return;
                }

           
                args.NewPad.Link(appsinkPad);
            };

            fileSrc.PadAdded += (o, args) =>
            {
                //args.Args[0] as 
                var decPad = h264parse.GetStaticPad("sink");

                if (decPad.IsLinked)
                {
                    return;
                }

                args.NewPad.Link(decPad);
            };

            qtdemux.PadAdded += (o, args) =>
            {
                //args.Args[0] as 
                var qPad = queue.GetStaticPad("sink");

                if (qPad.IsLinked)
                {
                    return;
                }

                args.NewPad.Link(qPad);
            };

            var pipeline = new Pipeline("video reader pipe");
            pipeline.Add(fileSrc, qtdemux, queue, h264parse, avdec, appSink);


            var linkResult = Element.Link(fileSrc, qtdemux);
            linkResult = Element.Link(qtdemux, queue);
            linkResult = Element.Link(queue, h264parse);
            linkResult = Element.Link(h264parse, avdec);
            linkResult = Element.Link(avdec, appSink);

            return pipeline;
        }

        public static void SearchFrameByNumber(Pipeline readerPipe, IEnumerable<string> videoFiles, int frameNumber)
        {
            if (readerPipe == null) throw new ArgumentNullException(nameof(readerPipe));


            var fileSrc = readerPipe.GetByName("filesrc");

            var appSink = (AppSink) readerPipe.GetByName("my_appsink");
            readerPipe.SetName("frame_stepper");

           
            foreach (var videoFile in videoFiles)
            {
                fileSrc["location"] = videoFile;

                readerPipe.SetState(State.Playing);


                var step = 1; //fn тоже с 1 начинается
                while (step < frameNumber)
                {
                    var sample = appSink.PullSample();
                    var fn = $"{Path.GetFileNameWithoutExtension(videoFile)}_{step}.jpeg";
                    SaveImg(sample,Path.Combine("d:\\test_out\\",fn));
                    step++;
                }

                readerPipe.SetState(State.Ready);
                
            }
        }