obs-webrtc: Adjust RtcpNackResponder from bitrate

Before we improperly used the default value set by libdatachannel. At
higher bitrates the cache would be undersized. Because of the undersized
cache we wouldn't have enough NACK history to fix the stream.

plugins/obs-webrtc/whip-output.cpp

@@ -21,6 +21,9 @@ const uint8_t audio_payload_type = 111;
 const char *video_mid = "1";
 const uint8_t video_payload_type = 96;
 
+// Convert Kbps to 'How many 1500 Byte packets in 5 seconds'
+const float videoNackStorageFactor = 125.0 / 1500.0 * 5.0;
+
 WHIPOutput::WHIPOutput(obs_data_t *, obs_output_t *output)
 	: output(output),
 	  is_av1(false),
@@ -162,7 +165,8 @@ void WHIPOutput::ConfigureVideoTrack(std::string media_stream_id,
 
 	video_sr_reporter = std::make_shared<rtc::RtcpSrReporter>(rtp_config);
 	packetizer->addToChain(video_sr_reporter);
-	packetizer->addToChain(std::make_shared<rtc::RtcpNackResponder>());
+	packetizer->addToChain(std::make_shared<rtc::RtcpNackResponder>(
+		videoNackStorageFactor * video_bitrate));
 
 	video_track = peer_connection->addTrack(video_description);
 	video_track->setMediaHandler(packetizer);