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MPEG-H Audio Decoding and Metadata Analysis
Posted on Tuesday, September 22, 2020
MPEG-H Audio Decoding and Metadata Analysis

Sept. 22, 2020 - StreamXpert now decodes MPEG-H audio and shows associated metadata in a concise way. Broadcasters can use it for confidence monitoring - checking that the audio actually decodes and that all parameters are configured properly. Equipment manufacturers can inspect and verify the MPEG-H audio stream and metadata in their product's output.

MPEG-H "3D" audio is a next-generation audio-coding standard that is a further development of AAC audio and includes new technologies. It has been developed by MPEG and Fraunhofer IIS to deliver customizable audio for any device, from theater to mobile phone. By sending separate audio channels to the end device and mixing the streams there, the best audio experience can be achieved for every situation. The user can select individual streams such as language or extra audio commentary, and even the listening position can be adjusted. The broadcaster determines which options the listener can adjust.

The new audio standard is gaining momentum. It has been on air since 2017 on TV networks in South Korea under ATSC 3.0, and it has been selected for various new broadcast channels to be launched, amongst others in China and Brazil.

A key technique in MPEG-H is the use of 'audio objects', each of which has a specific position in space. The audio objects are rendered for the speaker layout used, producing a realistic 3D sound field. MPEG-H enables transmission of 7.1 audio with several audio objects in the same bandwidth as todays 5.1 surround broadcasts. By separating commentary language from music tracks and including those as separate audio objects, better compression can be achieved while at the same time giving the user more control over position and presence of language and commentary tracks.

StreamXpert can analyze MPEG-H audio in both OTT and transport streams. The analyzer provides an in-depth view of the structure of the MPEG-H stream.

PID Info

MPEG-H audio info is shown in the PID tree, similar to how this is done for Dolby AC-4 audio.

At the top level, you can see the stream's total bitrate, profile (L4), level (low complexity) and sample rate.

Following are signal groups and audio-scene info, which are further explained in the screenshots below.

Signal Groups

Signal groups are the physical sample streams available in the stream. An MPEG-H decoder uses these signals to compose an output audio stream.

For each signal group the number of signals and the corresponding loudspeaker layout are shown. Custom speaker layouts can be defined.

Audio-Scene Info

Metadata defining 'groups' of signals. Three types of groups are defined: (standard) group of signals, switch groups and group presets.

Each group has a descriptive name for use in the listeners user interface. Additional attributes determine the listener options to control the presence, location and availability of the groups.

Switch Groups

A switch group defines a selection of choices from which a listener can select one in the user interface.

In the example on the left the user can select the audio "Language" (a string available in other languages) between English, French, German and Portugese.

Group Presets

Each group preset describes an audio composition consisting of a number of groups and/or a number of switch groups.

If there is more than one group preset, the listener can select the group preset of his/her choice. If switch groups are available in a preset, the listener can select one of the elements from the switch group.

MPEG-H Audio Decoding

The proof of the pudding is in the eating, so in addition to showing metadata, StreamXpert can also decode MPEG-H audio. Audio decoding parameters can be configured in a decoding user interface that is dynamically built from the Audio Scene Info metadata. When the audio scene changes, the user interface is updated accordingly.

With the addition of MPEG-H audio decoding and showing metadata, StreamXpert keeps up with the latest broadcast standards. The new MPEG-H functionality is included in the standard StreamXpert v2.13 package and freely available to those who have purchased their StreamXpert license or latest maintenance extension less than 12 months ago.

Model: StreamXpert