RTSP-specific features

Transport protocols

The RTSP protocol supports several underlying transport protocols, that are chosen by clients during the handshake with the server:

UDP: the most performant, but doesn’t work when there’s a NAT/firewall between server and clients.
UDP-multicast: allows to save bandwidth when clients are all in the same LAN, by sending packets once to a fixed multicast IP.
TCP: the most versatile.

The default transport protocol is UDP. To change the transport protocol, you have to tune the configuration of your client of choice.

Encryption

Incoming and outgoing RTSP streams can be encrypted with TLS, obtaining the RTSPS protocol. A TLS certificate is needed and can be generated with OpenSSL:

openssl genrsa -out server.key 2048
openssl req -new -x509 -sha256 -key server.key -out server.crt -days 3650

Edit mediamtx.yml and set the encryption, serverKey and serverCert parameters:

rtspEncryption: optional
rtspServerKey: server.key
rtspServerCert: server.crt

Streams can be published and read with the rtsps scheme and the 8322 port:

rtsps://localhost:8322/mystream

Corrupted frames

In some scenarios, when publishing or reading from the server with RTSP, frames can get corrupted. This can be caused by several reasons:

When the transport protocol is UDP (which is default one), packets sent to the server might get discarded because the UDP read buffer size is too small. This can be noticed in logs through the “RTP packets lost” message. Try increasing the UDP read buffer size:
```
rtspUDPReadBufferSize: 1000000
```
If the source of the stream is a camera:
```
paths:
  test:
    source: rtsp://..
    rtspUDPReadBufferSize: 1000000
```
Both these options require the net.core.rmem_max system parameter to be equal or greater than rtspUDPReadBufferSize:
```
sudo sysctl net.core.rmem_max=100000000
```
When the transport protocol is UDP (which is the default one), packets sent from the server to readers might get discarded because the write queue is too small. This can be noticed in logs through the “reader is too slow” message. Try increasing the write queue:
```
writeQueueSize: 1024
```
The stream is too big and it can’t be transmitted correctly with the UDP transport protocol. UDP is more performant, faster and more efficient than TCP, but doesn’t have a retransmission mechanism, that is needed in case of streams that need a large bandwidth. A solution consists in switching to TCP:
```
rtspTransports: [tcp]
```
In case the source is a camera:
```
paths:
  test:
    source: rtsp://..
    rtspTransport: tcp
```
The stream throughput is too big to be handled by the network between server and readers. Upgrade the network or decrease the stream bitrate by re-encoding it.