Introduction

A low-latency HLS (LL-HLS) playback feature has been introduced in Ant Media Server version 2.11 and above. It reduces traditional HLS latency from 8–12 seconds to approximately 2–5 seconds, making it ideal for near-real-time streaming applications.

What is LL-HLS?

Low Latency HLS (LL-HLS) is a streaming protocol designed to minimize latency in live streaming. Traditional HLS can have latency ranging from 8 to 12 seconds, while LL-HLS reduces this to around 2-5 seconds.

LL-HLS achieves this by using smaller video segments (called parts) that allow the video player to start playback before an entire segment is completed.

Prerequisites

• Ant Media Server Enterprise Edition v2.12 or later: LL-HLS plugin compatible from this version.
• LL-HLS Plugin: Purchase the plugin by emailing [email protected] or via the Ant Media website
• Supported Player: Use a player that supports LL-HLS. We recommend testing with hls.js or Dolby Player first.

Key Differences: HLS vs. LL-HLS

Standard HLS	Low Latency HLS (LL-HLS)
Latency: 8-12 secs	Latency: 2-5 secs
Segment-based	Part-based (smaller chunks)
Larger file sizes	Smaller, more frequent parts

How to Enable LL-HLS in Ant Media Server

LL-HLS is a paid plugin offered by the Ant Media Server. So before using LL-HLS, you need to purchase and install the plugin on your Ant Media Server.

For more information about plugin structure in Ant Media Server, take a look at the Ant Media Server Plugins.

Step 1: Install the LL-HLS Plugin

1. Install the Plugin

   • Upload/copy the plugin file to your instance running the Ant Media Server.

   • Run the following commands to install:

     sudo unzip low-latency-hls-plugin.zip
     cd low-latency-hls-plugin
     sudo ./install_low-latency-hls-plugin.sh
     sudo service antmedia restart

Step 2: Publish a Stream

Ant Media Server provides LL-HLS endpoints for all ingested streams. You can check the publish live streams section to learn how to publish streams using different protocols with Ant Media Server. For this example, let's publish with WebRTC.

Stream Configuration Requirements

For LL-HLS to function correctly, your stream configuration must meet the following criteria:

1. Adaptive Bitrate (ABR): ABR must be enabled.
2. GOP Size: The Group of Pictures (GOP) size must be set to 1 or 2 seconds maximum.
   • Example: If the framerate is 30 fps, set the GOP size to 30 or 60.

Hardware Encoding Settings:

If you are using hardware encoding (e.g., h264_nvenc), you must configure the following parameters to ensure stability:

"encoderParameters": {
    "h264_nvenc": {
      "rc": "cbr",
      "gop_size": "60", // or 30 for 1 second
      "no-scenecut": "1" // Ensure no additional keyframes are added between scene changes
    }
}

1. Access the WebRTC Publish Page

   • Open the following URL in your browser: https://yourserver.com:5443/live/?id=stream1

   • Replace the domain with your Ant Media server's domain.

   • You can use stream1 or any custom stream ID.

2. Start Publishing the Stream

   • Click the Start Publishing button on the page.

   

Step 3: Play the Stream with LL-HLS

1. Open a Video Player

   We recommend using hls.js or Dolby Player for initial testing and latency verification.

   • hls.js demo player
   • Dolby Player
   • From AMS v2.12 onwards, the LL-HLS playback is supported via the AMS Embedded Player as well. To learn more about embedded web player, check here.

2. Enter the LL-HLS URL

   In the player, enter the following URL to play the stream:

   https://yourserver.com:5443/live/streams/ll-hls/stream1/stream1__master.m3u8

   

   • Ensure two underscores (__) exist between the stream ID and master.m3u8.

   • URL pattern: https://{YOUR_SERVER}:{5443}/{APP}/streams/ll-hls/{STREAM_ID}/{STREAM_ID}__master.m3u8

   • If you are using the Ant Media Server player, then the URL pattern would be as follows:

     https://{YOUR_SERVER DOMAIN}:5443/{AppName}/play.html?name={streamId}&playOrder=ll-hls

Customize LL-HLS

You can fine-tune LL-HLS settings in the Advanced section of the application settings of the Ant Media Server web panel. These settings allow you to adjust the behavior of LL-HLS to meet specific needs, like controlling segment durations or playlist updates.

Customization Parameters

1. partTargetDurationMs

The maximum duration of partial segments in milliseconds.

• Recommended: 1000 ms (round value).
• Troubleshooting: If you experience playback issues, try setting this to a non-round value slightly above 1 second (e.g., 1002 ms).

"partTargetDurationMs": 1000

2. targetDuration

Target duration for media files

"targetDuration": 8

3. slidingWindowEntries

Number of media segments retained in the playlist (default: 5). Increasing this value can improve stability but may consume more resources.

"slidingWindowEntries": 5

4. deleteFiles

Determines whether old media files are deleted after being removed from the playlist (default: true). It is set to false if you want to keep old segments.

"deleteFiles": true

5. program

Indicates if a VOD-style program is being captured, which means all segments are retained in the playlist (default: false).

"program": false

6. addDateTime

Controls whether the date and time are added to media file names (default: true)

"addDateTime": true

7. receiveDataTimeout

Timeout duration in seconds after which the segmenter pauses if no data is received (default: 10). 0 means never.

"receiveDataTimeout": 0

8. exitOnReceiveDataTimeout

If set to true, the segmenter will exit when the receiveDataTimeout is reached. Otherwise, it will just pause (default: false).

"exitOnReceiveDataTimeout": false

9. fileCompleteCommand

Command executed when a media or index file is completed. You can use %P for the full path and %F for the file name.

"fileCompleteCommand": "/path/to/script %P %F"

10. fileDeleteCommand

Command executed when a media or index file is deleted after being removed from the playlist.

"fileDeleteCommand": "/path/to/delete_script %P %F"

11. quiet

If set to true, only error messages will be displayed in the logs (default: false).

"quiet": false

12. abrDirectMuxing

Only effective if using ABR. If direct muxing to LL-HLS is enabled, the original stream will also be directly re-muxed to LL-HLS alongside ABR (default: true). This rarely should be set to FALSE, mostly for debugging purposes.

"abrDirectMuxing": true

13. noFloatingPointDuration

If set, the segmenter will try to split segments into round numbers (default: true). Recommended true, since players might have problems handling decimal numbers

"noFloatingPointDuration": true

14. partsHoldback

Suggests to the player how many parts it should stay behind the live edge to ensure smooth playback (default: 3).

"partsHoldback": 3

15. deleteFilesOnStreamEnd

If set, LL-HLS related stream files will be deleted when the stream completes (default: false).

"deleteFilesOnStreamEnd": false

Apply Customization

To apply the above settings, add them under the customSettings section in the Ant Media Server application's Advanced settings:

"customSettings": {
  "plugin.ll-hls": {
    "partTargetDurationMs": 1000,
    "targetDuration": 4,
    "slidingWindowEntries": 5,
    "deleteFiles": true,
    "program": false,
    "addDateTime": true,
    "receiveDataTimeout": 10,
    "exitOnReceiveDataTimeout": false,
    "fileCompleteCommand": "/path/to/script %P %F",
    "fileDeleteCommand": "/path/to/delete_script %P %F",
    "quiet": false,
    "abrDirectMuxing": true,
    "noFloatingPointDuration": true,
    "partsHoldback": 3,
    "deleteFilesOnStreamEnd": false
  }
}

You can easily enable Low-Latency HLS (LL-HLS) on Ant Media Server with this guide. For a more detailed explanation of LL-HLS and its related properties, check the Low-latency HLS blogpost.

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⏩ LL-HLS – Streaming in the Fast Lane! 🏎️💨

Congratulations! You've successfully set up LL-HLS with Ant Media Server. Your viewers can now enjoy live streams with significantly reduced latency, enhancing their real-time viewing experience. With LL-HLS, you've embraced a modern streaming protocol that balances performance and compatibility. Your content is now delivered faster, keeping your audience engaged and satisfied.