add more example doc

Author: wanglei.w

README.md

@@ -5,7 +5,7 @@ ffmpeg-go is golang port of https://github.com/kkroening/ffmpeg-python
 check ffmpeg_test.go for examples.
 
 
-# example 
+# Examples
 
 ```go
 split := Input(TestInputFile1).VFlip().Split()
@@ -21,7 +21,77 @@ err := Concat([]*Stream{
     Run()
 ```
 
-# view
+## Task Frame From Video
+
+```bash
+func ExampleReadFrameAsJpeg(inFileName string, frameNum int) io.Reader {
+	buf := bytes.NewBuffer(nil)
+	err := ffmpeg.Input(inFileName).
+		Filter("select", ffmpeg.Args{fmt.Sprintf("gte(n,%d)", frameNum)}).
+		Output("pipe:", ffmpeg.KwArgs{"vframes": 1, "format": "image2", "vcodec": "mjpeg"}).
+		WithOutput(buf, os.Stdout).
+		Run()
+	if err != nil {
+		panic(err)
+	}
+	return buf
+}
+
+reader := ExampleReadFrameAsJpeg("./sample_data/in1.mp4", 5)
+img, err := imaging.Decode(reader)
+if err != nil {
+    t.Fatal(err)
+}
+err = imaging.Save(img, "./sample_data/out1.jpeg")
+if err != nil {
+    t.Fatal(err)
+}
+```
+result : 
+
+![image](./examples/sample_data/out1.jpeg)
+
+
+## Show Ffmpeg Progress
+
+see complete example at: [showProgress](./examples/showProgress.go)
+
+```bash
+func ExampleShowProgress(inFileName, outFileName string) {
+	a, err := ffmpeg.Probe(inFileName)
+	if err != nil {
+		panic(err)
+	}
+	totalDuration := gjson.Get(a, "format.duration").Float()
+
+	err = ffmpeg.Input(inFileName).
+		Output(outFileName, ffmpeg.KwArgs{"c:v": "libx264", "preset": "veryslow"}).
+		GlobalArgs("-progress", "unix://"+TempSock(totalDuration)).
+		OverWriteOutput().
+		Run()
+	if err != nil {
+		panic(err)
+	}
+}
+ExampleShowProgress("./sample_data/in1.mp4", "./sample_data/out2.mp4")
+```
+
+result 
+
+```bash
+progress:  .0
+progress:  0.72
+progress:  1.00
+progress:  done
+```
+
+## Use Ffmpeg-go With Open-cv (gocv) For Face-detect
+
+see complete example at: [opencv](./examples/opencv.go)
+
+result: ![image](./examples/sample_data/face-detect.jpg)
+
+# View Graph
 
 function view generate [mermaid](https://mermaid-js.github.io/mermaid/#/) chart, which can be use in markdown or view [online](https://mermaid-js.github.io/mermaid-live-editor/)
 

examples/opencv.go

@@ -62,23 +62,25 @@ func openCvProcess(xmlFile string, reader io.ReadCloser, w, h int) {
 		if img.Empty() {
 			continue
 		}
+		img2 := gocv.NewMat()
+		gocv.CvtColor(img, &img2, gocv.ColorBGRToRGB)
 
 		// detect faces
-		rects := classifier.DetectMultiScale(img)
+		rects := classifier.DetectMultiScale(img2)
 		fmt.Printf("found %d faces\n", len(rects))
 
 		// draw a rectangle around each face on the original image,
 		// along with text identifing as "Human"
 		for _, r := range rects {
-			gocv.Rectangle(&img, r, blue, 3)
+			gocv.Rectangle(&img2, r, blue, 3)
 
 			size := gocv.GetTextSize("Human", gocv.FontHersheyPlain, 1.2, 2)
 			pt := image.Pt(r.Min.X+(r.Min.X/2)-(size.X/2), r.Min.Y-2)
-			gocv.PutText(&img, "Human", pt, gocv.FontHersheyPlain, 1.2, blue, 2)
+			gocv.PutText(&img2, "Human", pt, gocv.FontHersheyPlain, 1.2, blue, 2)
 		}
 
 		// show the image in the window, and wait 1 millisecond
-		window.IMShow(img)
+		window.IMShow(img2)
 		if window.WaitKey(10) >= 0 {
 			break
 		}