Prefer TCP again

This changes the behaviour of "Protocol" option of device configuration,
which affects how the source RTSP stream is being consumed.

Historically, TCP was preferred.
Then, since
01bac09 ("Refactored input device and added option to select AUTO rtp protocol")
UDP with fallback to TCP became the default ("AUTO" mode).
This makes picture in recordings prone to smearing, so it was decided to
switch back to TCP by default.

Previously, fallback to TCP was done in our code; this commit makes use
of FFmpeg's "rtsp_flags=+prefer_tcp" which accomplishes suitable
behaviour: try TCP, fallback to UDP.

lib/lavf_device.cpp

@@ -75,7 +75,6 @@ void lavf_device::stop()
 int lavf_device::start()
 {
 	if (ctx) return 0;
-	bool using_tcp = false;
 
 	AVDictionary *avopt_open_input = NULL;
 	AVInputFormat *input_fmt = NULL;
@@ -88,11 +87,10 @@ int lavf_device::start()
 
 	if (!strncmp(url, "rtsp://", 7))
 	{
-		if (rtp_protocol == RTP_PROTOCOL_TCP || tcp_fallback)
-		{
-			av_dict_set(&avopt_open_input, "rtsp_flags", "+prefer_tcp", 0);
-			tcp_fallback = false;
-			using_tcp = true;
+		switch (rtp_protocol) {
+			case RTP_PROTOCOL_TCP:  av_dict_set(&avopt_open_input, "rtsp_transport", "tcp", 0); break;
+			case RTP_PROTOCOL_UDP:  av_dict_set(&avopt_open_input, "rtsp_transport", "+udp+udp_multicast", 0); break;
+			case RTP_PROTOCOL_AUTO: av_dict_set(&avopt_open_input, "rtsp_flags", "+prefer_tcp", 0); break;
 		}
 	}
 
@@ -118,14 +116,6 @@ int lavf_device::start()
 		av_strerror(re, error_message, sizeof(error_message));
 		bc_log(Error, "Failed to open stream. Error: %d (%s)", re, error_message);
 		ctx = NULL;
-
-		if (rtp_protocol == RTP_PROTOCOL_AUTO && !using_tcp)
-		{
-			bc_log(Info, "Falling back to TCP connection");
-			tcp_fallback = true;
-			return start();
-		}
-
 		return -1;
 	}
 

lib/lavf_device.h

@@ -52,7 +52,6 @@ class lavf_device : public input_device
 private:
 	char url[1024];
 	int rtp_protocol = RTP_PROTOCOL_AUTO;
-	bool tcp_fallback = false;
 	char error_message[512];
 
 	AVFormatContext *ctx;