RTMP Ingest Setup and Usage

This article provides an overview of how to set up and use Phenix's RTMP ingest.

RTMP publishing requires a stream key. For instructions on how to find your stream key, see How do I find my stream key?.

Default RTMP publishing capabilities can be set when creating a Channel or a Room. If capabilities are passed with the RTMP stream key, these default settings will be ignored.

Your encoder's configuration must be set up to ensure that it is not introducing unnecessary latency. The number one issue that causes high latency is not using the correct low-latency settings on the local encoder.

For details on setting up your source, please refer to the page for your encoder (see the menu on the left).

To characterize the latency of the encoder, try measuring the lag using ffplay with the "nobuffer" setting. Using ffplay is always recommended to determine the baseline latency when evaluating encoder settings. The argument will be similar to:

ffplay -fflags nobuffer <url>

If the latency is not extremely low, that indicates that the encoder is not configured correctly for low latency.

Check that encoder settings are set to the lowest possible values that will provide acceptable results, such as baseline profile, CBR, 5 Mbps, 1-second GOP size.

Phenix supports H.264-encoded video as ingest, and recommends using Constrained Baseline Profile up to Level 5.2 with a maximum frame size of 36864 macro-blocks for best performance. Be sure to verify that features such as scene change detection are not enabled to keep the encoding consistent. Some video feeds using may appear to work initially, but will fail when certain unsupported features are used (e.g., when the encoding is optimized for a high motion scene).

The source bitrate must be less than 8Mbps, with no spikes in the bitrate exceeding that value. There must be zerolatency interleaving, and no grouping of audio or video packets. The audio and video packets should be in strict increasing order based on the timestamp in the signal.

The audio must be 48kHz AAC, either mono or stereo, MPEG-2 ADTS, not MPEG-4 LOAS/LATM.

• Set bitrate output higher than the Phenix target bitrate for your desired quality level from the supported quality capabilities. Examples:

  • When sd capability is set in the stream key, Phenix targets 830kbps, so the RTMP encoder should be set to output 1,500kbps
  • When hd capability is set in the stream key, Phenix targets 1,600kbps, so the RTMP encoder should be set to output 2,500kbps.
  • When fhd capability is set in the stream key, Phenix targets 3,000kbps, so the RTMP encoder should be set to output 5,000kbps.

• Frame rate: set to 30

  • Certain video encoding/decoding pipelines will buffer a certain number of frames

• Keyframe interval: set to 1 second

• For x264 encoding, CPU Usage Preset: set to veryfast

• Profile: set to baseline

• Tune

  • OBS: set to zerolatency
  • Wirecast: set x264 command line options → -tune zerolatency

In OBS, these recommended settings will look like the following:

For details on API usage, please refer to the RTMP REST API.

An example RTMP URL is:

rtmp://ingest.phenixrts.com:80/ingest/96characterStreamKey;capabilities=hd,multi-bitrate,tags=my-awesome-stream-id

Where 96characterStreamKey is the stream key to be used when publishing, which can be found in the Customer Portal under the Properties tab for a Channel or Room.

Base URL: rtmp://ingest.phenixrts.com:80/ingest/

Streamkey Structure: <streamkey><separator><Phenix RTMP Ingest Options>

where the separator can be either be a semicolon ; or a pipe |. See RTMP Ingest Options for additional details.

Typical Example: rtmp://ingest.phenixrts.com:80/ingest/KK7rLBnoTaReAlvaLidStreAmkeYQCE1wRl;capabilities=hd,multi-bitrate;tags=myStreamTag

Common Capabilities:

• Set desired highest quality layer with sd (standard definition), hd (high definition), or fhd (full high definition)
• Include the multi-bitrate capability to automatically transcode to multiple quality layers for ABR delivery
• Include streaming capability to create HLS and DASH formatted streams available if applicable

Related Documentation:

• RTMP Ingest Options
• Complete List of capabilities

In OBS, the recommended settings will look like the following:

If you choose not to specify any capabilities, the following default capabilities will be used: fhd,multi-bitrate,playout-buffer=PT0.23S,high-fidelity

If some capabilities are specified, but quality layer is not, then the sd quality layer will be used.