improve H264/H265 examples (#355) (#375) (#398)

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

@@ -12,16 +12,17 @@ import (
 	"github.com/bluenviron/gortsplib/v4/pkg/format"
 	"github.com/bluenviron/gortsplib/v4/pkg/format/rtph264"
 	"github.com/bluenviron/gortsplib/v4/pkg/url"
+	"github.com/bluenviron/mediacommon/pkg/codecs/h264"
 	"github.com/pion/rtp"
 )
 
 // This example shows how to
 // 1. connect to a RTSP server
-// 2. check if there's a H264 media
-// 3. decode H264 into RGBA frames
-// 4. encode the frames into JPEG images and save them on disk
+// 2. check if there's a H264 media stream
+// 3. decode the H264 media stream into RGBA frames
+// 4. convert frames to JPEG images and save them on disk
 
-// This example requires the ffmpeg libraries, that can be installed in this way:
+// This example requires the FFmpeg libraries, that can be installed with this command:
 // apt install -y libavformat-dev libswscale-dev gcc pkg-config
 
 func saveToFile(img image.Image) error {
@@ -77,18 +78,18 @@ func main() {
 	}
 
 	// setup H264 -> raw frames decoder
-	h264RawDec, err := newH264Decoder()
+	frameDec, err := newH264Decoder()
 	if err != nil {
 		panic(err)
 	}
-	defer h264RawDec.close()
+	defer frameDec.close()
 
 	// if SPS and PPS are present into the SDP, send them to the decoder
 	if forma.SPS != nil {
-		h264RawDec.decode(forma.SPS)
+		frameDec.decode(forma.SPS)
 	}
 	if forma.PPS != nil {
-		h264RawDec.decode(forma.PPS)
+		frameDec.decode(forma.PPS)
 	}
 
 	// setup a single media
@@ -97,6 +98,7 @@ func main() {
 		panic(err)
 	}
 
+	iframeReceived := false
 	saveCount := 0
 
 	// called when a RTP packet arrives
@@ -110,9 +112,18 @@ func main() {
 			return
 		}
 
+		// wait for an I-frame
+		if !iframeReceived {
+			if !h264.IDRPresent(au) {
+				log.Printf("waiting for an I-frame")
+				return
+			}
+			iframeReceived = true
+		}
+
 		for _, nalu := range au {
 			// convert NALUs into RGBA frames
-			img, err := h264RawDec.decode(nalu)
+			img, err := frameDec.decode(nalu)
 			if err != nil {
 				panic(err)
 			}