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Dash Playback with CMAF

What Is CMAF (Common Media Application Format)?​

The Common Media Application Format (CMAF) is essentially a new format to reduce HTTP delivery latency. It is a new standard that aims to reduce the cost, complexity, and latency of streaming (typically 3-5 seconds). CMAF can be used in DASH or HLS. Both LL-DASH (Low Latency Dash) and LL-HLS (Low Latency HLS) are supported by Ant Media Server in the CMAF format.

How to use CMAF​

In Ant Media Server v2.4.3 and earlier, you must enable it in your application's configuration file. It is now possible to enable it directly from the Ant Media dashboard starting with version 2.5.0.

To play Dash stream, provide streamId as the name and dash as the playOrder parameters in the URL shown below.

https://AMS-domain-name:5443/WebRTCAppEE/play.html?name=test&playOrder=dash

In order to enable the dash programmatically, follow below steps:

1. Open the following file with your favorite editor

/usr/local/antmedia/webapps/WebRTCAppEE/WEB-INF/red5-web.properties

2. Enable DASH by adding the following property to the file above.

settings.dashMuxingEnabled=true

If you want to enable LL-HLS (an experimental feature), you also need to set the following properties:

settings.dash.llHlsEnabled=true

3. Restart the Ant Media Server

sudo service antmedia restart

There are a few more options for CMAF and their default values. You can assume that the following values are in use if they are not specified in the properties file:

#Duration of segments in mpd files.
settings.dashSegDuration=6
#Fragments are a property of fragmented MP4 files. Typically a fragment consists of moof + mdat.
settings.dashFragmentDuration=0.5

#Target latency
settings.dashTargetLatency=3.5

#DASH window size. Number of files in manifest
settings.dashWindowSize=5

#DASH extra window size. Number of segments kept outside of the manifest before removing from disk
settings.dashExtraWindowSize=5

#Enable low latency dash. This settings is effective if dash is enabled
settings.dash.llEnabled=true

Note: If you're using Dash streaming with ABR enabled, make sure the following property is enabled in your application's red5-web.properties file.

settings.forceAspectRationInTranscoding=false

The value is false by default. Check here for more information on this property.

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