examples/encode_video: add log

This helps to visualize how the send/receive API works.

doc/examples/encode_video.c

@@ -42,6 +42,9 @@ static void encode(AVCodecContext *enc_ctx, AVFrame *frame, AVPacket *pkt,
     int ret;
 
     /* send the frame to the encoder */
+    if (frame)
+        printf("Send frame %3"PRId64"\n", frame->pts);
+
     ret = avcodec_send_frame(enc_ctx, frame);
     if (ret < 0) {
         fprintf(stderr, "Error sending a frame for encoding\n");
@@ -57,7 +60,7 @@ static void encode(AVCodecContext *enc_ctx, AVFrame *frame, AVPacket *pkt,
             exit(1);
         }
 
-        printf("Write frame %3"PRId64" (size=%5d)\n", pkt->pts, pkt->size);
+        printf("Write packet %3"PRId64" (size=%5d)\n", pkt->pts, pkt->size);
         fwrite(pkt->data, 1, pkt->size, outfile);
         av_packet_unref(pkt);
     }