• How to control transcoded audio with audio encoding parameters

    This article describes how to adjust the audio in the transcoded output from Wowza Transcoder through the use of audio encoding parameters. Users with advanced encoding knowledge can log all of the audio encoding parameters that are available, and their current values, and use this information to adjust the transcoding parameters for transcoded output renditions.

    Contents


    Logging available audio encoding parameters
    Configuring audio encoding parameters
    More resources

    Logging available audio encoding parameters


    When using Wowza Transcoder, you can log all available audio encoding parameters with their current values for a given <Encode> block to the wowzastreamingengine_access.log file. To do this, open the transcoder template file in a text editor and add the following property to the <Properties> container in each <Encode> block in the transcoder template:
    <Property>
    	<Name>logAudioEncodingParameters</Name>
    	<Value>true</Value>
    	<Type>Boolean</Type>
    </Property>
    A section of the data logged in the wowzastreamingengine_access.log file might look like this:
    # long: channel copy: 0=donothing, 1=copy-left-over-right, 2=copy-right-over-left
    mainconcept.channel_copy: 0
    # long: variable bitrate mode: 0 = off
    mainconcept.vbr: 0
    # long: crc protection: 0=off, 1=on
    mainconcept.protect_adts_stream: 0
    # long: temporal noise shaping (tns) algorithm: 0=off, 1=on
    mainconcept.tns: 1
    # long: high efficiency: 0=off, 1=HE-v1, 2=HE-v
    mainconcept.he: 0
    # long: high frequency cut-off
    mainconcept.hf_cutoff: 0
    # long: aac object type
    mainconcept.aac_object_type: 2
    # long: mpeg version: 6=MPEG2_AAC_AUDIO, 7=MPEG4_AAC_AUDIO, 16=MPEG4_AAC_AUDIO_PSP
    mainconcept.mpeg_version: 7
    #
    You can then use this information as a basis for adjusting the transcoded audio output using the available audio encoding parameters that are logged.

    Configuring audio encoding parameters


    You must use a text editor to configure audio parameters in the transcoder template files ([install-dir]/transcoder/templates) in your Wowza Streaming Engine™ installation. They can't be configured using Wowza Streaming Engine Manager.

    Open the transcoder template file in a text editor and add a <Parameter> section to the <Audio>/<Parameters> container in each <Encode> block that you want to modify, as shown in the example below. A single template can have multiple <Encode> blocks (one for each encoded bitrate in the output stream). Then restart the Wowza media server for the changes to take effect.

    Note: Older versions of the example transcoder templates may not have a <Parameters> container for the <Audio> encoding section. Add this container if it's missing from your transcoder template.

    Example configuration

    As an example, for this audio parameter defined as available in the wowzastreamingengine_access.log file:
    # long: channel copy: 0=donothing, 1=copy-left-over-right, 2=copy-right-over-left
    mainconcept.channel_copy: 0
    #
    You can add the following <Parameter> section to the <Audio>/<Parameters> container in an <Encode> block in your template file:
    <Parameter>
    	<Name>mainconcept.channel_copy</Name>
    	<Value>1</Value>
    	<Type>Long</Type>
    </Parameter>
    In the above example, we've added the mainconcept.channel_copy audio parameter to an <Encode> block and changed its value to 1 (copy the left audio channel over the right audio channel).

    More resources


    How to set up and run Wowza Transcoder

    Originally Published: For Wowza Streaming Engine on 03-07-2014.

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