About Wowza ClearCaster MPEG-TS and SRT output tuning options

Learn about MPEG-TS and SRT output tuning options for Wowza ClearCaster™ broadcasts.

  • Wowza ClearCaster supports SRT version 1.4.
  • Adaptive network encoding over SRT is not currently supported.


When you create a broadcast with an MPEG-TS or SRT output from a ClearCaster appliance, use the built-in Other destination. For the Encoding Template, select either Output MPEGTS UDP or Output SRT. You can send multicast or unicast MPEG-TS streams.

With this setup, you'll need to provide a JSON-formatted output URL to set up your broadcast. This URL includes a number of tuning parameters for the output stream. 

For example, an MPEG-TS stream looks something like this:
url: "{\"url\":\"udp://\",\"implementation\":\"notifypacket\"}"

While an SRT stream looks something like this:
url: "{\"url\":\"udp://\",\"implementation\":\"srt\"}"

  • The port specified in the Output URL automatically updates the port that the ClearCaster appliance uses for streaming while a broadcast is live.
  • If you're including an Output URL in a custom template, you'll need to include a JSON escape using a backslash (\) like those in the examples above.
  • If you're manually adding the Output URL to a field in the Create Broadcast dialog, you don't need to include a JSON escape using a backslash (\). For example:
    • url: {"url":"udp://","implementation":"notifypacket"}
    • url: {"url":"udp://","implementation":"srt"}

Tuning parameters

You can include parameters in the URL JSON object to tune your MPEG-TS or SRT output.

Required parameter for all output URLs

ParameterData TypeDescription
urlStringThe output URL with a port number. For example, upd://

Notifypacket and SRT parameters

Use these tuning parameters for MPEG-TS or SRT streams, unless otherwise specified.

ParameterData TypeDescription
implementationStringThe implementation for the output stream. Use notifypacket for MPEG-TS and srt for SRT. Default is notifypacket.
pmtIntervalIntegerThe time, in milliseconds, between PMT packets. Default is 1000.
mpegtsAudioGroupCountIntegerThe number of audio packets per PES packet. Default is 3.
pcrBufferTimeIntegerThe time, in milliseconds, that the PCR clock runs behind the video DTS. Default is 200.
mpegtsPacketsPerBlockIntegerThe number of 188-byte TS packets per UDP packet. Default is 7.
mpegtsAlwaysSendZeroPacketLenBooleanIf true, always sends PES lengths of 0. Default is true.
pacingRateDoubleA value used to calculate the pacing rate of the socket (totalBitrate * pacingRate) for MPEG-TS streams only. Default is 1.25.
srtSocketSettingsArrayAn array of SRT socket settings for SRT streams only.
For example, "srtSocketSettings":[{"option":"SRTO_SNDBUF","value":65000,"type":"Integer"}] 
Default is an empty array, [].

SRT socket settings

Use these settings and their values in an array for the srtSocketSettings parameter. Specify the option, value, and type for each object in the array, as shown in the example above.

OptionData TypeDescription
SRTO_MSSIntegerThe maximum segment size. Default of 1500 is the maximum size of the UDP packet and can be only decreased, unless under unusual dedicated network settings.
SRTO_SNDSYNBooleanIf true, synchronous (blocking) send mode is enabled. Default is true.
SRTO_RCVSYNBooleanIf true, synchronous (blocking) receive mode is enabled. Default is true.
SRTO_ISNIntegerThe value of the ISN (Initial Sequence Number), which is the first sequence number put on the first sent UDP packet carrying SRT data payload. Valid only for sockets after srt_connect or srt_accept.
SRTO_FCIntegerThe flight flag size (window size). Default is 25600.
SRTO_SNDBUFIntegerThe maximum buffer in the sending queue. Default is 8192 × (1500-28).
SRTO_RCVBUFIntegerThe size of the UDT receiving buffer. Default is 8192 × (1500-28).
SRTO_LINGERIntegerThe number of seconds that the socket waits for unsent data when closing. Default is 180. Recommended value for SRT is 0.
SRTO_UDP_SNDBUFIntegerThe size of the UDP sending buffer. Default is 65536. SRT recommended value is 1024*1024.
SRTO_UDP_RCVBUFIntegerThe size of the UDP receiving buffer. Default is 8192 × 1500.
SRTO_RENDEZVOUSBooleanIf true, enables the rendezvous connection mode. Default is true.
SRTO_SNDTIMEOIntegerSends a timeout in milliseconds. Default is -1.
SRTO_RCVTIMEOIntegerReceives a timeout in milliseconds. Default is -1.
SRTO_REUSEADDRBooleanIf true, reuses an existing port instead of creating a new one. Default is true.
SRTO_MAXBWIntegerThe maximum bandwidth, in bytes per second, that the connection can use. Default is -1, infinite. SRT recommended value is 0, relative to input rate.
SRTO_STATEIntegerThe current UDT connection state. Read-only.
SRTO_EVENTIntegerThe current available events associated with the socket.  Gets bit flags set according to the current active events on the socket. Read-only.
SRTO_SNDDATAIntegerThe size of data in the sending buffer.
SRTO_RCVDATAIntegerThe size available data in the receive buffer.
SRTO_SENDERIntegerThe sender mode for encryption or TSBPD handshake, independent of the connection mode. Default is false.
SRTO_TSBPDMODEIntegerIf true, enables timestamp-based packet delivery mode (TSBPD). Default is true. Tx set origin timestamp, Rx deliver packet at origin time plus delay.
SRTO_LATENCYIntegerThis flag sets both SRTO_RCVLATENCY and SRTO_PEERLATENCY to the same latency value, in milliseconds. Default is 0.
Note: To determine the recommended value for SRTO_LATENCY, perform a test broadcast to the intended destination, and make note of the Round Trip Time displayed in the Wowza ClearCaster Manager Monitor tab. The SRTO_LATENCY value should be four times the Round Trip Time for the test broadcast.
SRTO_TSBPDDELAYIntegerDeprecated. Use SRTO_LATENCY instead.
SRTO_INPUTBWIntegerThe estimated input stream rate or sender nominal input rate, in bytes per second. Default is 0.
SRTO_OHEADBWIntegerThe maximum bandwidth ceiling based on percentage over input stream rate. Applies when UDT_MAXBW is 0 (auto). Default is 25%.
SRTO_PASSPHRASEStringThe password-based key derivation function 2 (PBKDF2) passphrase. Default is 0, with crypto disabled.
SRTO_PBKEYLENIntegerThe crypto key length in bytes {16, 24, 32}. Default is 16 (128-bit) if you've set a passphrase. If you don't have cryto enabled, default is 0.
SRTO_KMSTATEIntegerThe keying material exchange status (UDT_SRTKmState).
SRTO_IPTTLIntegerThe IPv4 time to live (passthrough for system sockopt IPPROTO_IP/IP_TTL).
SRTO_IPTOSIntegerThe IPv4 type of service (passthrough for system sockopt IPPROTO_IP/IP_TOS).
SRTO_TLPKTDROPIntegerIf true, enables receiver packet drop. Default is true.
SRTO_SNDDROPDELAYIntegerThe extra delay towards latency for sender TLPKTDROP decision. Default is 0. Use -1 to turn off the setting.
SRTO_NAKREPORTBooleanIf true, enables the receiver to send periodic NAK reports until a lost packet is retransmitted or intentionally dropped. Default is true.
SRTO_VERSIONIntegerThe local SRT version.
SRTO_PEERVERSIONIntegerThe peer SRT version from the SRT handshake.
SRTO_CONNTIMEOIntegerThe connection timeout, in milliseconds. Default is 3000. The connect timeout is 10 times the value set for the rendezvous mode.
SRTO_SNDKMSTATEIntegerThe current state of the encryption on the peer side.
Valid values:
  • 0 (SRT_KM_S_UNSECURED) - No encryption
  • 1 (SRT_KM_S_SECURING) - Stream encrypted, exchanging keying material
  • 2 (SRT_KM_S_SECURED) - Stream encrypted, keying material exchanged, decrypting successful
  • 3 (SRT_KM_S_NOSECRET) - Stream encrypted but no secret is available to decrypt the keying material
  • 4 (SRT_KM_S_BADSECRET) - Stream encrypted but the secret doesn't match and cannot decrypt the keying material
SRTO_RCVKMSTATEIntegerThe current state of the encryption on the agent side.
Valid values:
  • 0 (SRT_KM_S_UNSECURED) - No encryption
  • 1 (SRT_KM_S_SECURING) - Stream encrypted, exchanging keying material
  • 2 (SRT_KM_S_SECURED) - Stream encrypted, keying material exchanged, decrypting successful
  • 3 (SRT_KM_S_NOSECRET) - Stream encrypted but no secret is available to decrypt the keying material
  • 4 (SRT_KM_S_BADSECRET) - Stream encrypted but the secret doesn't match and cannot decrypt the keying material
SRTO_RCVLATENCYIntegerThe TsbPd receiver delay, in milliseconds, to absorb a burst of missed packet retransmission. In live mode, default is 120. In buffer mode, default is 0.
SRTO_PEERLATENCYIntegerThe minimum value of the TsbPd receiver delay, in milliseconds, for the opposite, peer side. Default is 0.
SRTO_MINVERSIONIntegerThe minimum SRT version needed for the peer. Peers with an earlier version will be rejected from connecting. Default is 0.
SRTO_STREAMIDStringA string set to a socket and passed to the accepted socket of the listener. Limited to 512 characters. See SRT Access Control Guidelines for more information.
SRTO_CONGESTIONStringThe congestion controller used for the socket transmission. The type must be exactly the same on both connecting parties, or the connection is rejected. Default is live.
SRTO_MESSAGEAPIBooleanIf true, uses the message API. Default is true.
SRTO_PAYLOADSIZEIntegerThe maximum payload size sent in one UDP packet. For live mode, default is 1316. Use 0 if unlimited.
SRTO_TRANSTYPEIntegerThe transmission type for the socket. This setting sets parameters associated with the selected type to their default values.
Valid values:
  • 0 (SRTT_LIVE)
  • 1 (SRTT_FILE)
Default is 0 (SRTT_LIVE). 
SRTO_KMREFRESHRATEIntegerThe number of packets to be transmitted after which the encryption key is switched to a new key.
SRTO_KMPREANNOUNCEIntegerThe interval between when a new encryption key is sent and when switchover occurs. This value also applies to the subsequent interval between when switchover occurs and when the old encryption key is decommissioned.
SRTO_STRICTENCBooleanIf true, both connection parties must have the same password set (including empty, that is, with no encryption). If the password doesn't match or only one side is unencrypted, the connection is rejected. Default is true.
SRTO_IPV6ONLYIntegerSets a system socket flag IPV6ONLY. When set to 0, a listening socket binding an IPv6 address also accepts IPv4 clients so that their addresses are formatted as IPv4-mapped IPv6 addresses. Default is -1, meaning this option is not set and the platform default value is used.
SRTO_PEERIDLETIMEOIntegerThe peer-idle timeout, in milliseconds. The maximum time of silence heard from a peer. If this time is passed, connection is considered broken on timeout. Default is 5000.

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