SRT Target

SRT Target properties for Script Engine. Streams the composed video and audio over SRT (Secure Reliable Transport) to any SRT-capable receiver (decoder appliance, contribution gateway, IRD, cloud ingest). SRT is the broadcast-industry standard for delivering live video over unmanaged IP networks (the public internet, 4G/5G bonded modems) — packet loss recovery and timestamping make it tolerant of glitchy links where RTMP would simply drop. Useful for studio-to-cloud contribution feeds, remote venue uplinks, point-to-point links between facilities, and any time you need a low-latency, resilient transport over the open internet. Supports up to four parallel audio program tracks for multi-language broadcasts.

Property	Type	Access	Description
`AutoStart`	`bool`	`get/set`	When On, the SRT target connects automatically when the project loads.
`ShowAdvancedOptions`	`bool`	`get/set`	Reveals advanced/expert properties in the panel (encoder tuning, reconnect tuning, debug counters). Off by default.
`SrtBaseAddress`	`string`	`get/set`	Base SRT URL in `srt://host:port` form. The host can be an IP, a DNS name, or a macro: `@@LocalIP()` resolves to this machine's local IP, `@@HostName()` to the machine name. For listener mode (receiver dials in to us) typically point to `0.0.0.0`. Treat as sensitive when targeting private cloud ingest.
`SrtOptions`	`string`	`get/set`	SRT URL query parameters appended after `?`. Common keys: `mode=caller\\|listener`, `latency=200000` (microseconds — typical 120–500 ms), `pkt_size=1316`, `passphrase=...`, `streamid=...`. Tune `latency` higher for noisy links, lower for low-glass-to-glass delivery.
`SrtStreamKey`	`string`	`get/set`	Optional SRT stream id (also called streamid). Many cloud ingests (Haivision Hub, Wowza, Cloudflare, AWS Elemental) require this for routing — receivers identify the publisher by this string. Treat as sensitive.
`SimulateLatencyEnabled`	`bool`	`get/set`	Enable simulated send latency (debug/testing aid). [default=false]. When on, each outgoing frame is held on the sender thread by `Simulated base latency` plus a time-varying component (see `Simulated latency pattern`). Used to reproduce variable-latency and congested links for SRT input synchronization tests. Leave off in production.
`SimulatedBaseLatencyMs`	`int`	`get/set`	Constant added send delay in milliseconds when latency simulation is enabled. [min=0, max=3000, default=0].
`SimulatedJitterMs`	`int`	`get/set`	Peak-to-peak latency variance in milliseconds around the base when simulation is enabled. [min=0, max=3000, default=0]. How the variance evolves over time is set by `Simulated latency pattern`.
`SimulatedLatencyPattern`	`SrtSimulatedLatencyPattern`	`get/set`	How the simulated latency evolves over time: `Static`, `RandomWalk`, `Sine`, or `StepSchedule` (steps between base and base+jitter each period — reproducible congestion events).
`SimulatedLatencyPeriodMs`	`int`	`get/set`	Period in milliseconds for the Sine / RandomWalk / StepSchedule latency patterns. [min=100, max=60000, default=2000].
`SrtConnectionString`	`string`	`get`	The full SRT URL Composer will dial, assembled from `SrtBaseAddress`, `SrtOptions`, and `SrtStreamKey` (read-only). Useful for verifying the resolved URL before connecting.
`OutputVideoBitrate`	`OutputVideoBitrate`	`get/set`	Target video bitrate. Match this to the available uplink bandwidth and the receiver's configured input. Typical values: 3 Mbit/s for 1080p contribution, 1.5 Mbit/s for 720p, 6+ Mbit/s for high-quality contribution feeds.
`H264BFrameDistance`	`H264BframeDistance`	`get/set`	Number of B-frames between reference frames in each GOP. Higher values improve compression efficiency at the cost of latency and decoder compatibility — set to Zero for low-latency contribution and live broadcast.
`VideoCompressionGopSize`	`VideoCompressionGopSize`	`get/set`	GOP (Group of Pictures) length in frames — controls keyframe spacing. Typical values: 1x or 2x framerate (e.g. 30 or 60 frames at 30 fps). Shorter GOPs recover faster from packet loss but cost compression efficiency.
`H264Profile`	`H264Profile`	`get/set`	H.264 profile (`baseline`, `main`, `high`). `baseline` is most universally compatible; `main`/`high` deliver better compression at the cost of decoder support on legacy devices.
`UseAdvanceCbrConfiguration`	`bool`	`get/set`	When On, sends with constant bitrate (CBR) — preferred for SRT contribution because most receivers and decoder appliances expect a steady rate. When Off, the encoder uses VBR which can starve under-provisioned links.
`MaxVideoRateMultiplier`	`float`	`get/set`	Multiplier on the configured bitrate that limits how high the encoder is allowed to swing. Default 1.0 — increase only if your network can absorb peaks.
`MinVideoRateMultiplier`	`float`	`get/set`	Multiplier on the configured bitrate that sets the floor (minimum). Default 1.0 — keep at 1.0 for true CBR; lower for more freedom on simple scenes.
`BufferSizeMultiplier`	`float`	`get/set`	Multiplier on the encoder's rate-control buffer size. Default 1.0 — larger buffers smooth out bitrate at the cost of latency.
`H264EncodingQualitySpeed`	`H264EncodingQualitySpeed`	`get/set`	x264 speed/quality preset. `veryfast`/`superfast` are the right pick for live encoding — slower presets give better quality but won't keep up in real time.
`H264Tune`	`H264Tune`	`get/set`	x264 tuning preset. Use `zerolatency` for live contribution to remove any look-ahead delay from the encoder.
`H264EncodingThreads`	`H264EncodingThreads`	`get/set`	Number of CPU threads used by the software H.264 encoder. More threads = lower per-frame latency but higher CPU. Ignored when NVENC is enabled.
`UseNvenc`	`bool`	`get/set`	When On, encode using the NVIDIA hardware encoder (NVENC) — much lower CPU load and recommended for any machine with a recent NVIDIA card. When Off, fall back to the software (x264) encoder.
`UseHevc`	`bool`	`get/set`	When On, encode with HEVC (H.265) using NVENC instead of H.264. HEVC gives better quality per bit and is required only for SEI timecode carriage (see `TimecodeCarriage`); the ST 2038 transport embeds timecode with H.264 too. Implies NVENC — HEVC has no software-encoder path here, so this takes precedence over `UseNvenc`.
`NvencAdvancedOptions`	`string`	`get/set`	NVENC encoder parameters as a JSON object. Tweak only when you know what you're doing — defaults are tuned for low-latency live contribution. Keys map directly to NVENC options (`preset`, `rc`, `gpu`, `delay`, etc.).
`EmbedTimecode`	`bool`	`get/set`	When On, embed an SMPTE timecode into the outgoing stream so a downstream SRT input — or any receiver — can read it back. The carriage is chosen by `TimecodeCarriage`: video SEI (requires HEVC) or a codec-agnostic SMPTE ST 2038 ancillary stream. With SEI and a non-HEVC codec a warning is logged and no timecode is sent.
`TimecodeCarriage`	`TimecodeTransport`	`get/set`	How the embedded timecode is carried: in-stream video SEI (HEVC only) or a separate SMPTE ST 2038 ancillary-data stream (codec-agnostic — works with H.264 — and readable without software video decoding). Only used when `EmbedTimecode` is On.
`TimecodeStartTime`	`TimecodeStartMode`	`get/set`	Where the embedded timecode starts counting from when streaming begins (the first written frame): 00:00:00:00, or the wall-clock time of day. Only used when `EmbedTimecode` is On. How closely `Time of day` then keeps up with the clock depends on the project frame rate: at 24 / 25 / 30 / 50 / 60 it is exact; at 29.97 / 59.94 it is correct to within about 70 ms, because drop-frame counting corrects in two-frame steps once a minute; at 23.98 it cannot track the clock at all and runs about 0.1% slow (roughly 43 seconds behind by midday, 86 seconds by the end of the day), because timecode labels 24 frames per second of 23.98 material and SMPTE defines no drop-frame scheme for that rate. At 23.98 the value is a running counter, not a clock reading.
`SrtAudioChannelOneEncoder`	`SrtAudioEncoder`	`get/set`	AAC encoder mode for audio program 1 (mono, stereo, or unused). Set to `Unused` to skip this audio program. Program 1 is normally the main mix.
`SrtAudioChannelOneMapping`	`AudioChannelMapping`	`get/set`	Selects which scene audio channel pair is encoded into program 1 (e.g. `OneTwo`, `ThreeFour`). Use this to route specific scene channels to specific SRT programs — typically 1+2 for the main mix.
`SrtAudioChannelOneBitRate`	`AacBitRate`	`get/set`	AAC bitrate for audio program 1. Typical values: 128 kbit/s for stereo broadcast, 64 kbit/s for mono commentary.
`SrtAudioChannelOneLanguage`	`string`	`get/set`	ISO 639 language tag (e.g. `eng`, `spa`, `fra`) embedded in program 1's metadata. Player UIs use this to label the audio track in language pickers.
`SrtAudioChannelTwoEncoder`	`SrtAudioEncoder`	`get/set`	AAC encoder mode for audio program 2. Set to `Unused` if you only need a single audio program. Otherwise pick mono/stereo to suit the source mix.
`SrtAudioChannelTwoMapping`	`AudioChannelMapping`	`get/set`	Scene audio channel pair routed to program 2. Often used for an alternate-language commentary feed (e.g. channels 3+4).
`SrtAudioChannelTwoBitRate`	`AacBitRate`	`get/set`	AAC bitrate for audio program 2.
`SrtAudioChannelTwoLanguage`	`string`	`get/set`	ISO 639 language tag for program 2 (e.g. `spa` for Spanish).
`SrtAudioChannelThreeEncoder`	`SrtAudioEncoder`	`get/set`	AAC encoder mode for audio program 3. Set to `Unused` if not needed.
`SrtAudioChannelThreeMapping`	`AudioChannelMapping`	`get/set`	Scene audio channel pair routed to program 3 (e.g. channels 5+6).
`SrtAudioChannelThreeBitRate`	`AacBitRate`	`get/set`	AAC bitrate for audio program 3.
`SrtAudioChannelThreeLanguage`	`string`	`get/set`	ISO 639 language tag for program 3.
`SrtAudioChannelFourEncoder`	`SrtAudioEncoder`	`get/set`	AAC encoder mode for audio program 4. Set to `Unused` if not needed.
`SrtAudioChannelFourMapping`	`AudioChannelMapping`	`get/set`	Scene audio channel pair routed to program 4 (e.g. channels 7+8).
`SrtAudioChannelFourBitRate`	`AacBitRate`	`get/set`	AAC bitrate for audio program 4.
`SrtAudioChannelFourLanguage`	`string`	`get/set`	ISO 639 language tag for program 4.
`WarnOnLowAverageBitrate`	`bool`	`get/set`	When On, raise a warning if the outgoing bitrate falls below 10% of the configured target — usually a sign the encoder is starving or the network is congested.
`ReconnectInterval`	`ReconnectInterval`	`get/set`	How long to wait between reconnect attempts after a dropped SRT connection. Five seconds is a sensible default.
`MaxOutputQueueSize`	`int`	`get/set`	Maximum number of encoded packets queued for the network before back-pressure triggers. [min=150, max=500, default=150]. Larger queues hide brief network slowdowns at the cost of added latency.
`OutputBufferAllowFrameSkipping`	`bool`	`get/set`	When On, allow Composer to drop frames if the output queue fills up — preserves stream continuity on a slow link at the cost of brief visual stutter.
`UseAlternateConnectionMode`	`bool`	`get/set`	Use the alternate (newer) SRT connection path. Default On — only switch off if instructed by support to fall back to legacy behaviour.
`LogBitrateToDisk`	`bool`	`get/set`	When On, write per-second bitrate samples to a CSV on disk for post-mortem analysis (read-only, debug). Use only when troubleshooting.
`ConnectionStatus`	`ConnectionStatus`	`get`	Current SRT connection status (Disconnected, Connecting, Connected, Reconnecting). Read-only. Useful in scripts to gate downstream actions on a live link.
`StartCommand`	`Command`	`get`	Connects to the SRT receiver (or starts listening for a caller in listener mode) and begins streaming.
`StopCommand`	`Command`	`get`	Stops the encoder and tears down the SRT connection.
`ReconnectCommand`	`Command`	`get`	Forces an immediate reconnect of the live SRT connection without stopping the target. API-only and hidden from the UI; invoke via `/api/invokecommand` with command `ReconnectCommand`. Only executable while connected.
`ComponentLog`	`ComponentLog`	`get`	In-panel mini-log of recent connection events, warnings, and errors. Quick way to see what the SRT writer last reported without opening the full log file.
`UpTimeSinceStart`	`string`	`get`	How long this target has been streaming, formatted as `HH:MM:SS` (read-only).
`OutgoingBitRate`	`string`	`get`	Current outgoing bitrate as a human-readable string (e.g. "3.0 Mbit/s"). Read-only. Use to verify the stream is actually pushing data over the wire.
`MinilogTime`	`DateTime`	`get`	Timestamp of the most recent log entry (read-only).
`AudioChannelUsed`	`string`	`get`	Summary of how many audio programs the encoder has bound (read-only). Useful in scripts to confirm the multi-language setup is active.
`NumInitialReconnects`	`long`	`get`	Number of reconnect attempts before the very first successful connect (read-only, debug). High counts indicate the receiver was slow to come up.
`NumAutoReconnectsperformed`	`int`	`get`	Number of automatic reconnects since the target started (read-only). A growing number means the link is unstable — check network or receiver logs.
`CurrentSrtEndPoint`	`string`	`get`	The fully resolved SRT URL Composer is currently dialling, with all macros (`@@LocalIP()`, `@@HostName()`) expanded (read-only).
`ErrorCount`	`int`	`get`	Cumulative count of errors logged since the target started (read-only). Pair with `LastErrorDateTime` in scripts to flag fresh errors.
`LastErrorDateTime`	`DateTime`	`get`	Timestamp of the most recent error (read-only).
`WarningCount`	`int`	`get`	Cumulative count of warnings since the target started (read-only).
`LastWarningDateTime`	`DateTime`	`get`	Timestamp of the most recent warning (read-only).

Inherits from: AbstractTarget, NamedModel.

See also: SRT Target in Targets — user-facing introduction, screenshots, and section summaries.