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Dolby’s Audio Solution for IPTV

Dolby has a long history of developing technologies and products to address the needs of broadcasters and operators. The introduction of IPTV brings its own unique set of requirements—and Dolby has developed the ideal solution: Dolby® Digital Plus.

Based on our long-established Dolby Digital technology, Dolby Digital Plus ideally complements the next-generation video codecs that are now being deployed. Currently, the most popular of these video compression standards is the ITU-T’s H.264 (also known as MPEG-4 AVC or MPEG-4 Part 10).

Just as Dolby Digital has been the worldwide de facto multichannel technology for MPEG-2 video over the past decade, Dolby Digital Plus promises to do the same for all H.264 applications, including IPTV, offering a high-quality listening experience and a solution that is backward compatible with the millions of existing Dolby Digital devices.


To provide a bit of perspective, 5.1-channel Dolby Digital at 384 kbps (192 kbps for stereo) is the industry-wide benchmark for broadcast-quality audio performance. Dolby Digital Plus significantly lowers the required data rate while maintaining the quality consumers expect from Dolby. This bandwidth savings is achieved through the introduction of unique, advanced audio coding tools.


Every Dolby Digital Plus decoder implementation includes a converter that outputs a fully compliant Dolby Digital bitstream, ensuring that every Dolby Digital Plus set-top box will be compatible with the millions of Dolby Digital A/V receivers and home theater systems installed in viewers’ homes today. The decoder also provides downmixed outputs for viewers with stereo or monophonic systems.

Because Dolby Digital Plus shares many fundamental characteristics with Dolby Digital, the conversion process is efficient and minimizes signal degradation from tandem coding effects that are frequently found with other codec solutions. 

Differentiating Features

A key factor in the success of many IPTV service offerings is differentiation. Dolby Digital Plus can help IPTV operators differentiate themselves from competitors by providing advanced features such as 7.1-channel surround sound and bitstream mixing.

In markets where competing service operators have been offering 5.1-channel surround sound, IPTV operators can go beyond 5.1 with Dolby Digital Plus and offer the new 7.1-channel audio also being introduced by the new Blu-ray Disc™ and HD DVD formats. Operators looking to differentiate their services will want to adopt and promote this premium feature, and the accompanying Dolby brand name will not only give it credibility but also provide a big boost to the operator’s marketing efforts.

Another feature offered by new entertainment formats like HD DVD and Blu-ray Disc is the ability to mix audio streams from two sources. Dolby Digital Plus supports this capability, and IPTV systems can take advantage of it by offering secondary tracks for applications such as services for the visually impaired, director’s commentary, or some other future need. The secondary stream can be multiplexed within the primary program, or it may originate from a separate source (for example, via the Internet). This stream-mixing feature of Dolby Digital Plus means that IPTV operators will be able to provide dynamically changing and up-to-date additional content to enhance their viewers’ experience.


The use of audio metadata is the best way to ensure a premium broadcast audio experience. Metadata allows content providers unprecedented control over how a program will be reproduced in the home and can ensure the best results for all home viewing environments. Metadata controls loudness between programs, commercials, and channels, and it optimizes other aspects of reproduction in the home, such as dynamic range control and downmixing of multichannel audio to stereo or mono. Metadata is best created during program creation and is carried along with the audio throughout the delivery chain.

Metadata is an integral part of Dolby Digital Plus, and provides a seamless link to other Dolby broadcast technologies, such as Dolby E and Dolby Digital.

Standards Adoption

Just as Dolby Digital is officially part of the broadcast industry standards (DVB, ATSC, SCTE, SMPTE), Dolby Digital Plus is also part of the ATSC broadcast standard and the DVB specifications for IPTV, digital cable, satellite, and terrestrial broadcasting.

Bitstream Syntax Specifications:

ATSC A/52B: Digital Audio Compression

ETSI TS 102 366 V1.1.1 Digital Audio Compression

Transport Stream Multiplexing Specifications:

ETSI TS 101 154 V1.7.1 (DVB)

ETSI TS 102 005 (for RTP)—DVB

ATSC A/53D Revision D

In packaged media, Dolby Digital Plus is part of both the HD DVD format and the Blu-ray Disc format. It is also supported by industry connectivity standards HDMI™ and IEEE 1394.

Product Implementations

Dolby manufactures stand-alone professional products for encoding, decoding, QC, and other applications. Dolby also makes hardware modules designed for integration into professional broadcast equipment (such as video encoders) made by other manufacturers. In addition, Dolby Digital Plus professional encoding, decoding, and transcoding (Dolby E/Dolby Digital to Dolby Digital Plus) functionality is available as licensed software.

Dolby Digital Plus is also available as a featured format inside the Dolby DP600 Program Optimizer, a file-based encoding/decoding/transcoding product ideally suited for IPTV VOD file preparation. The DP600 also corrects program loudness levels and associated metadata.

On the consumer side, Dolby Digital Plus is supported by major set-top box manufacturers, as well as the market’s four leading system-on-a-chip IC manufacturers.

Choose from the drop-down menus below to get Dolby professional reference material.