add *codec* to codec-related examples

examples/client-read-codec-h264-convert-to-jpeg/main.go

@@ -0,0 +1,145 @@
+package main
+
+import (
+	"image"
+	"image/jpeg"
+	"log"
+	"os"
+	"strconv"
+	"time"
+
+	"github.com/aler9/gortsplib"
+	"github.com/aler9/gortsplib/pkg/rtph264"
+	"github.com/aler9/gortsplib/pkg/url"
+)
+
+// This example shows how to
+// 1. connect to a RTSP server and read all tracks on a path
+// 2. check if there's a H264 track
+// 3. decode H264 into RGBA frames
+// 4. encode the frames into JPEG images and save them on disk
+
+// This example requires the ffmpeg libraries, that can be installed in this way:
+// apt install -y libavformat-dev libswscale-dev gcc pkg-config
+
+func saveToFile(img image.Image) error {
+	// create file
+	fname := strconv.FormatInt(time.Now().UnixNano()/int64(time.Millisecond), 10) + ".jpg"
+	f, err := os.Create(fname)
+	if err != nil {
+		panic(err)
+	}
+	defer f.Close()
+
+	log.Println("saving", fname)
+
+	// convert to jpeg
+	return jpeg.Encode(f, img, &jpeg.Options{
+		Quality: 60,
+	})
+}
+
+func main() {
+	c := gortsplib.Client{}
+
+	// parse URL
+	u, err := url.Parse("rtsp://localhost:8554/mystream")
+	if err != nil {
+		panic(err)
+	}
+
+	// connect to the server
+	err = c.Start(u.Scheme, u.Host)
+	if err != nil {
+		panic(err)
+	}
+	defer c.Close()
+
+	// find published tracks
+	tracks, baseURL, _, err := c.Describe(u)
+	if err != nil {
+		panic(err)
+	}
+
+	// find the H264 track
+	h264TrackID, h264track := func() (int, *gortsplib.TrackH264) {
+		for i, track := range tracks {
+			if h264track, ok := track.(*gortsplib.TrackH264); ok {
+				return i, h264track
+			}
+		}
+		return -1, nil
+	}()
+	if h264TrackID < 0 {
+		panic("H264 track not found")
+	}
+
+	// setup RTP/H264->H264 decoder
+	rtpDec := &rtph264.Decoder{}
+	rtpDec.Init()
+
+	// setup H264->raw frames decoder
+	h264RawDec, err := newH264Decoder()
+	if err != nil {
+		panic(err)
+	}
+	defer h264RawDec.close()
+
+	// if SPS and PPS are present into the SDP, send them to the decoder
+	sps := h264track.SafeSPS()
+	if sps != nil {
+		h264RawDec.decode(sps)
+	}
+	pps := h264track.SafePPS()
+	if pps != nil {
+		h264RawDec.decode(pps)
+	}
+
+	// called when a RTP packet arrives
+	saveCount := 0
+	c.OnPacketRTP = func(ctx *gortsplib.ClientOnPacketRTPCtx) {
+		if ctx.TrackID != h264TrackID {
+			return
+		}
+
+		// convert RTP packets into NALUs
+		nalus, _, err := rtpDec.Decode(ctx.Packet)
+		if err != nil {
+			return
+		}
+
+		for _, nalu := range nalus {
+			// convert NALUs into RGBA frames
+			img, err := h264RawDec.decode(nalu)
+			if err != nil {
+				panic(err)
+			}
+
+			// wait for a frame
+			if img == nil {
+				continue
+			}
+
+			// convert frame to JPEG and save to file
+			err = saveToFile(img)
+			if err != nil {
+				panic(err)
+			}
+
+			saveCount++
+			if saveCount == 5 {
+				log.Printf("saved 5 images, exiting")
+				os.Exit(1)
+			}
+		}
+	}
+
+	// setup and read all tracks
+	err = c.SetupAndPlay(tracks, baseURL)
+	if err != nil {
+		panic(err)
+	}
+
+	// wait until a fatal error
+	panic(c.Wait())
+}