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SRT file or SRT protocol? Two different things

SRT means two things: a subtitle file (SubRip, .srt) and a live streaming protocol (Secure Reliable Transport). How to tell which one you need and where each is used.

Updated November 5, 2026 · 5 min read

SRT is two unrelated things that happen to share three letters. An SRT file is a plain text subtitle file (SubRip, extension .srt): numbered lines of text with start and end times. SRT the protocol (Secure Reliable Transport) is a way to send a live video stream over the internet that copes with a weak connection. One is a document you upload next to a finished video; the other is a connection your encoder opens while you are live.

If someone asks you for "the SRT", the context tells you which: an editor or YouTube's caption screen wants the file; a broadcast engineer or an encoder setting wants the protocol.

Side by side

The SRT subtitle file

An SRT file is about as simple as a caption format gets. Each block has a number, a time range and one or two lines of text, with an empty line after it:

1
00:00:01,200 --> 00:00:03,800
Welcome to the weekly class.

2
00:00:04,000 --> 00:00:06,500
Today we start a new chapter.

There is no font, colour or position in it: the player decides how it looks. That is why it works almost everywhere. YouTube lists SRT among the caption files it accepts (YouTube Help: Supported subtitle and closed caption files, checked 5 November 2026). Its web cousin is VTT (WebVTT), defined by the W3C for HTML5 players (W3C: WebVTT).

In StreamLive Pro: open a project in Translate and subtitles, press Export and choose SRT — Subtitles. The file is UTF-8, and lines with Hebrew or another right-to-left script start with an invisible right-to-left mark so punctuation lands on the correct side. SRT, VTT and TXT are on every plan, the trial included. More: Export captions as SRT, VTT or ASS, and which one to use and Upload SRT captions to YouTube, step by step.

The SRT streaming protocol

SRT the protocol was created and open-sourced by Haivision, according to the SRT Alliance (SRT Alliance, checked 5 November 2026). It sends video over UDP and asks again for packets that went missing, within a time window you set, called latency. On a line that loses packets, for example a venue's shared Wi-Fi or a mobile connection, it keeps the stream going where RTMP tends to freeze. A passphrase encrypts the stream.

An SRT address has more parts than an RTMP one: the host and port, a passphrase, often a stream ID, the latency and a connection mode (caller, listener or rendezvous). Encoders such as OBS and vMix put these in one srt:// address or in separate fields.

In StreamLive Pro, two places:

• Sending to us. Every broadcast has an SRT address on the Encoder card, next to RTMP and RTMPS. You send SRT from OBS, vMix or a hardware encoder; we send the broadcast on to each network in the protocol that network takes. Encoder ingest is on the paid plans; the 7-day trial uses the browser studio. Step by step: Stream with SRT from OBS, vMix or a hardware encoder.
• Sending from us. A Custom SRT destination sends your broadcast to an SRT server you name, for example a TV station's receiver. See Stream to a custom RTMP or SRT server.

How SRT compares with RTMP and RTMPS on a bad line, on firewalls and on encryption: RTMP vs RTMPS vs SRT: which one to use and when.

How not to mix them up

• A file you can open in Notepad is a subtitle file. A protocol is never a file.
• An address that starts with srt:// is the protocol.
• A request after the event ("send me the SRT for the recording") is almost always the subtitle file.
• A request before the event ("can you take SRT?") is almost always the protocol.
• In OBS settings, SRT is the protocol. In YouTube Studio's subtitles screen, it is the file.

Common mistakes with each

With the subtitle file:

• Saving it in an old text encoding instead of UTF-8, so Hebrew turns into question marks. Our exports are UTF-8; re-saving in an old editor can break that.
• Editing the times by hand and leaving two lines that overlap. Most players then show one and skip the other.
• Uploading it in the wrong language slot on YouTube.

With the protocol:

• Pasting the address but not the passphrase, so the connection is refused.
• Setting the latency too low for a weak line. SRT can only recover packets inside that window.
• Testing at home on a wired line and assuming the venue's network allows outgoing UDP. Test at the venue, and keep RTMPS as a fallback.

Do you need either?

Frequently asked questions

Is an SRT file the same as SRT streaming?

No. An SRT file is a subtitle text file. SRT streaming is the Secure Reliable Transport protocol for sending live video. They only share the letters.

What does SRT stand for in subtitles?

It is short for SubRip, the name of the subtitle format. In streaming, SRT stands for Secure Reliable Transport.

Can I send SRT from OBS to StreamLive Pro?

Yes, on a paid plan. The Encoder card of each broadcast has an SRT address next to RTMP and RTMPS.

Can StreamLive Pro make an SRT subtitle file?

Yes. Export it from Translate and subtitles on any plan, the trial included.

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