How to deliver a lower-latency stream by using the Wowza Streaming Cloud REST API

The Wowza Streaming Cloud™ service allows you to deliver live streams to viewers over three protocols: RTMP and RTSP directly from the transcoder, and Apple HLS from a CDN endpoint. If latency is a concern, direct RTMP and RTSP playback is the faster option, but the number of concurrent viewers who can watch your stream this way is limited. Apple HLS delivery from a CDN endpoint, on the other hand, allows you to reach more viewers—and more geographically dispersed viewers—but the latency is greater.

This article explains how to use the Wowza Streaming Cloud REST API to deliver streams using a hybrid RTMP-HLS workflow to achieve reduced latency and a more scalable deployment. The delivery methods used in this article provide an example. You can choose to just use one, or customize the destinations and settings in whatever way makes sense for your streaming needs.

Note: For information about ultra low latency streaming, see the Wowza Streaming Cloud ultra low latency REST API quick start guide.

Contents

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About latency over RTMP and Apple HLS
Create a reduced-latency transcoder and passthrough output for direct RTMP playback
Add a Wowza CDN - HLS stream target
Reduce the chunk size of the HLS stream target
Assign the HLS target to the output
Get the playback URLs
More resources

About latency over RTMP and Apple HLS

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A lower-latency workflow can be used to deliver a stream directly from the Wowza Streaming Cloud transcoder (the origin server) to your audience over RTMP or RTSP playback URLs. Under optimal conditions—the viewer is close to your broadcast location, network conditions are good, and your source encoding settings are optimal—delivering a stream directly from the Wowza Streaming Cloud transcoder to viewers offers latency as low as 1 second. The advantage of this reduced latency, however, may be offset by the facts that the transcoder is limited to 100 maximum connections and latency increases the farther the viewer is located from the transcoder.

A second option for lower-latency streaming is to use a Wowza CDN - HLS stream target that parses the stream into small chunks, or short segments. By reducing the Apple HLS chunk size from the default 10 seconds to 2 seconds, you can achieve a latency of as low as 5 seconds. Apple HLS targets in Wowza Streaming Cloud have no restrictions on the number of viewers who can access the stream and they are widely distributed, with servers that are close to viewers wherever they watch. And because Apple HLS is based on HTTP, it performs well on all kinds of networks.

Create a reduced-latency transcoder and a passthrough output for direct RTMP playback

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Start by using the Wowza Streaming Cloud REST API to create a transcoder that receives video from a source encoder and delivers a passthrough stream to your targets. Use the following transcoder parameters for your reduced-latency workflow.

Reduced-latency transcoder parameters

 

Example request and response

Notes:

• For [key], substitute your API key or your access key as appropriate. For more information, see Locating and using API and access keys.
• For [version], substitute the version number of the API that you're using. For the current version, use v1.1.

Create the transcoder:
 

curl --header  'wsc-api-key: [key]' --header 'wsc-access-key: [key]' --header 'Content-Type: application/json' -X POST -d '{
   "transcoder": {
     "billing_mode": "pay_as_you_go",
     "broadcast_location": "eu_belgium",
     "buffer_size": 0,
     "delivery_method": "push",
     "low_latency": true,
     "name": "MyLowLatencyTranscoder",
     "play_maximum_connections": 100,
     "protocol": "rtmp",
     "stream_smoother": false,
     "transcoder_type": "passthrough"
   }
}' "https://api.cloud.wowza.com/api/[version]/transcoders/"

The command creates a passthrough transcoder with an id parameter (1234abcd in this example) but no outputs ("outputs": []). The details of the configured transcoder are listed in the response, which should look something like this:
 

{
  "transcoder": {
    "application_name": "app-1234",
    "billing_mode": "pay_as_you_go",
    "broadcast_location": "eu_belgium",
    "buffer_size": 0,
    "closed_caption_type": none,
    "created_at": "2016-04-22T13:33:16.575",
    "delivery_method": "push",
    "delivery_protocols": [
	"rtmp",
	"rtsp",
	"wowz"
    ],
    "direct_playback_urls": [],
    "disable_authentication": false,
    "domain_name": "[subdomain].entrypoint.cloud.wowza.com",
    "id": "1234abcd",
    "idle_timeout": 1200,
    "low_latency": true,
    "name": "MyLowLatencyTranscoder",
    "outputs": [],
    "password": "12345678",
    "play_maximum_connections": 100,
    "protocol": "rtmp",
    "recording": false,
    "source_port": 1935,
    "stream_name": "1a2a3a4a",
    "stream_smoother": false,
    "suppress_stream_target_start": false,
    "transcoder_type": "passthrough",
    "updated_at": "2016-04-22T13:33:16.575",
    "username": "client1",
    "watermark": false
   }
}

Create the passthrough output:
 

curl -X POST --header "Content-Type: application/json" --header "wsc-api-key: [key]" --header "wsc-access-key: [key]" -d '{
   "output": {
     "passthrough_audio": true,
     "passthrough_video": true,
     "stream_format": "audiovideo"
   }
}' "https://api.cloud.wowza.com/api/[version]/transcoders/[transcoder_id]/outputs"

The command creates the output with an id parameter (5678efgh in this example) but no targets ("targets": []). The details of the configured output are listed in the response, which should look something like this:
 

{
   "output": {
     "bitrate_audio": 0,
     "bitrate_video": 0,
     "created_at": "2016-04-28T11:01:26.044",
     "framerate_reduction": 0,
     "h264_profile": null,
     "id": "5678efgh",
     "keyframes": "follow_source",
     "name": "Video+Audio=Passthrough+Passthrough",
     "passthrough_audio": true,
     "passthrough_video": true,
     "stream_format": "audiovideo",
     "targets": [],
     "transcoder_id": "1234abcd",
     "updated_at": "2016-04-28T11:01:26.044"
   }
}

Add a Wowza CDN - HLS stream target

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Next, add a Wowza CDN stream target that delivers the stream to geographically distributed endpoints over Apple HLS.

Wowza CDN - HLS stream target parameters

Example request and response

Create the target:
 

curl --header 'wsc-api-key: [key]' --header 'wsc-access-key: [key]' --header 'Content-Type: application/json' -X POST -d '{
   "stream_target": {
     "name": "MyLowLatencyHLStarget",
     "provider": "akamai_cupertino",
     "type": "WowzaStreamTarget"
   }
}' "https://api.cloud.wowza.com/api/[version]/stream_targets/"

The command creates the target with an id parameter (3456mnop in this example). The details of the configured target are listed in the response, which should look something like this:
 

{
   "stream_target": {
     "chunk_size": "10,"
     "created_at": "2016-04-28T11:01:45.044",
     "hls_playback_url": "https://[wowzasubdomain]-i.akamaihd.net/hls/live/123456/29e0a1/playlist.m3u8",
     "id": "3456mnop",
     "name": "MyLowLatencyHLStarget",
     "primary_url": "rtmp://[entrypointserver].net/EntryPoint",
     "provider": "akamai_cupertino",
     "stream_name": "6f86005b",
     "type": "WowzaStreamTarget",
     "updated_at": "2016-04-28T11:01:45.044",
     "use_cors": false,
     "use_secure_ingest": false
   }
}

Reduce the chunk size of the HLS stream target

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Reduce the duration of the stream's HLS segments by specifying a small chunk size property for the target:
 

curl --header 'wsc-api-key: [key]' --header 'wsc-access-key: [key]' --header 'Content-Type: application/json' -X POST -d '{
  "property": {
    "key": "chunkSize",
    "section": "hls",
    "value": "2"
  }
}' "https://api.cloud.wowza.com/api/[version]/stream_targets/[stream_target_id]/properties/"

The command assigns a chunk size of 2 to the target (3456mnop in this example). The details of the target's property are listed in the response, which should look something like this:
 

{
   "property": {
     "key": "chunkSize",
     "section": "hls",
     "value": "2"
   }
}

Assign the HLS stream target to the output

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Assign the Apple HLS target to the output:
 

curl --header 'wsc-api-key: [key]' --header 'wsc-access-key: [key]' --header 'Content-Type: application/json' -X POST -d '{
   "output_stream_targets": {
     "stream_target_id": "3456mnop",
     "use_stream_target_backup_url": false
   }
}' "https://api.cloud.wowza.com/api/[version]/transcoders/[transcoder_id]/outputs/[output_id]/output_stream_targets/"

Get the stream target's playback URLs

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Get the Apple HLS and RTMP playback URLs:
 

curl --header 'wsc-api-key: [key]' --header 'wsc-access-key: [key]' https://api.cloud.wowza.com/api/[version]/stream_targets/[stream_target_id]/

More resources

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• Best practices for setting the segment duration
   
• Source encoding recommendations for low-latency streaming
   
• How to encode source video for Wowza Streaming Cloud

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