In Recast for Business, open Stream Inputs and choose + Stream Input. Pick RTMP or SRT — the choice is fixed once the input is created.
Recast then shows the values your encoder needs. Copy them from there rather than retyping them:
Note that an SRT input labels its credential STREAM ID, not Stream Key. It is the same value, under the name SRT uses for it.
Then confirm all three of these, or your stream will be refused:
A new stream input is switched off. Recast switches it on only when it is attached to a live, non-draft video. This is the most common reason a correctly configured encoder is rejected.
Version: any recent OBS release works for RTMP. For SRT you need OBS 25 or later, and OBS 30 or later is strongly preferred — SRT is a first-class protocol there, with fewer rough edges.
Use no more than 50% of your measured upload bandwidth. A 5000 kbps stream needs a genuine, sustained 10 Mbps up.
Settings → Output, with Output Mode set to Advanced:
CBR2veryfastmain(none)Settings → Audio: set Sample Rate to 48 kHz. This is a global OBS setting and changing it requires a restart, so do it before the day.
Settings → Output → Audio: set the track's bitrate to 128.
Settings → Video: set Output (Scaled) Resolution and Common FPS Values to match the tier you chose. Leave Base (Canvas) Resolution at your monitor's size.
Which URL? Recast displays rtmp://global-live.mux.com:5222/app as your RTMP STREAM URL, and that works. This guide uses rtmps:// on port 443 instead: it is the same Mux ingest wrapped in TLS, so your stream key is not sent in clear text, and port 443 passes through restrictive venue networks that block port 5222. Use whichever your encoder supports.
rtmps://global-live.mux.com:443/appUse RTMPS on port 443 rather than plain RTMP. It encrypts your stream key in transit and port 443 is open on effectively every network. If you need plain RTMP, the server is rtmp://global-live.mux.com:5222/app.
European users can use rtmps://eu-west.live.mux.com/app instead of the global URL.
Requires OBS 25 or later. OBS 30+ recommended.
OBS takes the whole SRT connection as a single URL, with the stream key and passphrase as query parameters — there are no separate fields.
srt://global-live.mux.com:6001?streamid=YOUR_STREAM_KEY&passphrase=YOUR_SRT_PASSPHRASE&pbkeylen=16&latency=500The URL is unforgiving and OBS gives poor feedback when it is malformed. Build it in a text editor, not in the OBS field:
YOUR_STREAM_KEY with the STREAM ID from RecastYOUR_SRT_PASSPHRASE with the PASSPHRASE from Recastpbkeylen=16 exactly as written — Mux requires a 128-bit key, and16 is how that is expressed here. This is the most common SRT mistake.
? before the first parameter and & between the othersIf your connection has a long round trip — bonded cellular, or streaming from another continent — raise latency=500 to latency=1000. Check with:
ping global-live.mux.com
The value should be at least four times the round-trip time.
If the status bar shows a red square, or the bitrate is far below what you set, stop and read the troubleshooting section rather than going live.
The sample rate trap. OBS defaults to 44.1 kHz on some systems. Mux expects 48 kHz. The symptom is not an error — it is silence, or audio that drifts out of sync over a long stream. Set it in Settings → Audio and restart OBS.
Streamlabs and other forks. They use the same underlying settings but move them. Look for a "Custom RTMP" or "Custom" destination and the same Server and Stream Key pair. SRT support varies by fork and version; if a fork will not accept an srt:// URL, use RTMPS.
Dynamic Bitrate. Under Settings → Advanced → Network, OBS offers "Dynamically change bitrate to manage congestion". It helps on an unstable connection but means you are no longer sending CBR. Leave it off for a wired venue; consider it on contended wifi where the alternative is dropping out.
Do not chase low latency. Recast streams run at standard latency (20–30 seconds) by design. Disabling B-frames or shortening the keyframe interval will not reduce what viewers see and will make the stream more fragile.
One protocol per stream input. A Recast stream input is created as either RTMP or SRT and cannot be switched afterwards. To move OBS from RTMP to SRT, create a new stream input of the right type.
Check the stream input is attached to a video and that the video is not a draft. OBS will show a healthy green connection while Recast rejects the stream, because the rejection happens after the connection is accepted.
Then wait a full 30 seconds before concluding anything is wrong.
pbkeylen missing or wrong — it must be 16Almost always the passphrase or the key length. Re-copy the passphrase from Recast and confirm pbkeylen=16 is present in the URL.
If both are right, raise latency to 1000 and try again — a value too low for your round-trip time produces exactly this symptom.
Nearly always bandwidth. Halve the bitrate; if it stabilises, the connection is the problem and not OBS.
Then: use a cable rather than wifi, disable any VPN, and stop other uploads on the network. On a laptop, plug in the power — some machines throttle hard on battery.
You have 30 minutes to reconnect before Recast treats the stream as ended.
Dropped frames mean the network cannot carry what you are sending. Reduce the bitrate or drop a tier.
If the status bar instead shows rendering or encoding lag, the bottleneck is your computer, not the network — lower the resolution, raise the CPU preset to veryfast or superfast, or switch to a hardware encoder.
Check Settings → Audio → Sample Rate is 48 kHz. This is the usual cause and it produces silence rather than an error.
For drift over a long stream, check that OBS is not mixing sources on different clocks — a USB microphone and a capture card, for example. OBS has a per-source Sync Offset in the audio mixer's advanced properties if you need to correct a fixed offset.
Include your OBS version, the protocol, your bitrate and resolution, your measured upload speed, and the log from Help → Log Files → Upload Current Log File. That log answers most questions on its own.
More detail: Recast live ingest reference
