Introduction

Latency is the time lag between when something is recorded in real life and when it is seen in a video player. There is, of course, some real time required to transmit a signal from the source through the internet to a viewer's player. Latency is aggravated by the fact that online video is transmitted in discrete chunks, called segments.

Latency can be reduced by shortening the length of the video segments, and the following sections will detail how you can do this in NextGen Live.

Understanding the Tradeoffs

Be aware that there is a tradeoff when reducing segment duration: to ensure uninterrupted playback, the player downloads a few video segments ahead of the current playback position (this is called buffering), so that they are ready when needed.

If you shorten the length of segments, keep the following in mind:

The player will be pre-fetching less video data, and chances of playback pausing while the player buffers additional segments will be increased
The customer's CDN will see increased request traffic
Apple's recommendation for standard live stream HLS is a 6-second segment duration. Shortening the segments may make the stream less stable in sub-optimal network conditions
Lower segment durations may impact stream stability for viewers with poor network connections

NextGen Live Approach

In NextGen Live, latency reduction is achieved by configuring the segment_duration_seconds parameter within the manifest configuration when creating a live channel via the Live API or by creating a custom ingest profile.

Key Differences from Legacy Live

Manifest-level configuration: Segment duration is set once in the manifest block, not per rendition
CMAF packaging: NextGen Live uses CMAF as the default packaging format for improved efficiency
Simplified configuration: Single parameter controls segment duration for all renditions
Better performance: CMAF packaging provides better cache hit ratios with reduced latency

Creating a Custom Ingest Profile

To create NextGen Live channels with reduced latency, you need to create a custom ingest profile that includes the manifest configuration with reduced segment duration. This profile can then be used when creating live events or channels.

Custom Profile Configuration

Create a custom ingest profile with the manifest block configured for reduced latency:

{
  "model_version": 2,
  "name": "Low Latency NextGen Live Profile",
  "description": "Custom profile for reduced latency NextGen Live streams with 2-second segments",
  "account_id": "your_account_id",
  "renditions": [
    {
      "media_type": "video",
      "label": "hls360p",
      "video_codec": "h264",
      "video_bitrate": 780,
      "decoder_bitrate_cap": 936,
      "decoder_buffer_size": 1170,
      "frame_rate": 30,
      "keyframe_rate": 0.5,
      "width": 640,
      "height": 360,
      "video_bframes": 3,
      "sample_aspect_ratio": "1:1",
      "deinterlace": "detect",
      "video_codec_profile": "main",
      "video_codec_level": "3",
      "video_reference_frames": 4,
      "allowed_frame_rates": [
        {
          "as_float": 23.97,
          "as_fraction": "24000/1001"
        },
        {
          "as_float": 24,
          "as_fraction": "24/1"
        },
        {
          "as_float": 25,
          "as_fraction": "25/1"
        },
        {
          "as_float": 29.97,
          "as_fraction": "30000/1001"
        },
        {
          "as_float": 30,
          "as_fraction": "30/1"
        }
      ]
    },
    {
      "media_type": "video",
      "label": "hls540p",
      "video_codec": "h264",
      "video_bitrate": 1500,
      "decoder_bitrate_cap": 1800,
      "decoder_buffer_size": 2250,
      "frame_rate": 30,
      "keyframe_rate": 0.5,
      "width": 960,
      "height": 540,
      "video_bframes": 3,
      "sample_aspect_ratio": "1:1",
      "deinterlace": "detect",
      "video_codec_profile": "main",
      "video_codec_level": "3.2",
      "video_reference_frames": 4,
      "allowed_frame_rates": [
        {
          "as_float": 23.97,
          "as_fraction": "24000/1001"
        },
        {
          "as_float": 24,
          "as_fraction": "24/1"
        },
        {
          "as_float": 25,
          "as_fraction": "25/1"
        },
        {
          "as_float": 29.97,
          "as_fraction": "30000/1001"
        },
        {
          "as_float": 30,
          "as_fraction": "30/1"
        }
      ]
    },
    {
      "media_type": "video",
      "label": "hls720p",
      "video_codec": "h264",
      "video_bitrate": 2400,
      "decoder_bitrate_cap": 2880,
      "decoder_buffer_size": 3600,
      "frame_rate": 30,
      "keyframe_rate": 0.5,
      "width": 1280,
      "height": 720,
      "video_bframes": 3,
      "sample_aspect_ratio": "1:1",
      "deinterlace": "detect",
      "video_codec_profile": "high",
      "video_codec_level": "4",
      "video_reference_frames": 4,
      "allowed_frame_rates": [
        {
          "as_float": 23.97,
          "as_fraction": "24000/1001"
        },
        {
          "as_float": 24,
          "as_fraction": "24/1"
        },
        {
          "as_float": 25,
          "as_fraction": "25/1"
        },
        {
          "as_float": 29.97,
          "as_fraction": "30000/1001"
        },
        {
          "as_float": 30,
          "as_fraction": "30/1"
        }
      ]
    },
    {
      "media_type": "video",
      "label": "hls1080p",
      "video_codec": "h264",
      "video_bitrate": 4500,
      "decoder_bitrate_cap": 5400,
      "decoder_buffer_size": 6750,
      "frame_rate": 30,
      "keyframe_rate": 0.5,
      "width": 1920,
      "height": 1080,
      "video_bframes": 3,
      "sample_aspect_ratio": "1:1",
      "deinterlace": "detect",
      "video_codec_profile": "high",
      "video_codec_level": "4.2",
      "video_reference_frames": 4,
      "allowed_frame_rates": [
        {
          "as_float": 23.97,
          "as_fraction": "24000/1001"
        },
        {
          "as_float": 24,
          "as_fraction": "24/1"
        },
        {
          "as_float": 25,
          "as_fraction": "25/1"
        },
        {
          "as_float": 29.97,
          "as_fraction": "30000/1001"
        },
        {
          "as_float": 30,
          "as_fraction": "30/1"
        }
      ]
    }
  ],
  "packages": [],
  "manifest": {
    "name": "playlist",
    "segment_duration_seconds": 2,
    "hls": {}
  },
  "profile_type": "live"
}

Key Configuration Parameters

Key Profile Parameters
Parameter	Description	Notes
`model_version`	Profile model version	Use `2` for NextGen Live profiles
`keyframe_rate`	Keyframes per second (fractional value)	`0.5` = 1 keyframe every 2 seconds
`segment_duration_seconds`	Length of each video segment in seconds	`2` for reduced latency, `6` for standard
`profile_type`	Type of profile	Must be `"live"` for live streaming profiles

Creating the Custom Profile

Follow these steps to create a custom ingest profile with reduced latency:

Navigate to the Admin module in Studio
In the left navigation, click Ingest Profiles
Select one of the existing NextGen Live ingest profiles or create a new one
Click Duplicate to create a new profile based on the selected one
In the new profile, change the name to "Low Latency NextGen Live Profile" (or another meaningful name)
Update the manifest block with segment_duration_seconds: 2 as shown in the example above
Click Save to create the profile

Using the Custom Profile

Once you've created the custom ingest profile, you can use it when creating live events or channels, similar to how you would use any other ingest profile.

In Studio

Open the Live module in Studio
Click Create Channel button
In the channel creation form, select your custom "Low Latency NextGen Live Profile" from the Renditions Profile dropdown

Select Low Latency Profile from Renditions Profile dropdown

Complete the rest of the channel configuration as normal
The reduced latency settings will be automatically applied based on your custom profile

Using the Live API

If you want reduced latency, and you use the Live API to create your live jobs, just create the channel as you normally do, and set segment_duration_seconds inside the manifest block to 2:

{
  "manifest": {
    "name": "playlist",
    "segment_duration_seconds": 2,
    "hls": {}
  }
}

Encoder Considerations

When using reduced segment duration, your encoder settings become more critical for maintaining stream stability.

Recommended Encoder Settings

Keyframe interval: Set to 60 frames (2 seconds at 30fps) to align with segment boundaries
Bitrate mode: Use Constant Bitrate (CBR) for more predictable segment sizes
Connection stability: Use a reliable network connection with sufficient bandwidth headroom