Audio and Video Encoding

Audio Data Reduction / Coding

IRT developed the data-reduction method MUSICAM for high-quality audio signals, which is based on subband coding and the use of masked thresholds. Our specialists also made crucial contributions to the enhancement of this technique and helped to standardise it internationally as ISO 11172-3 MPEG Audio and as Recommendation ITU-R BS 1115.

In fact, IRT won a renowned Emmy award in 2000 for MPEG audio coding.

Compatible Improvement of MPEG Layer II Audio Coding

The combination of Spectral Band Replication (SBR) with Layer II increases coding efficiency by up to 40 per cent in lower data-rate ranges. The decisive advantage lies in backwards compatibility: existing DAB receivers can decode the Layer II data stream from Layer II+SBR signals. Layer II+ could therefore constitute a compatible solution for more programmes in the DAB multiplex.

IRT conducted a study on the transmission behaviour of SBR-coded audio signals to determine the impact which increased error sensitivity of broadcast signals has on reception properties. The findings were compared with previous tests of normal Layer II signals conducted by the EUREKA 147 Consortium (DAB). It became clear that existing DAB coverage areas remain the same after the introduction of the Layer II+ Format, based on SBR coding, due to unchanged error sensitivity.

Official homepage of MPEG

Audio Watermarking

Watermarking is a type of modern copyright management which embeds a digital signal in audio data. Watermarking can also be used to transmit supplementary data in audio signals. This technique, which IRT is helping to develop, is crucial during various phases of the production process and for the storage or transfer of audio content. In future, several different watermarks will most likely overlap during the course of the overall production/transmission chain.

MPEG Video Coding

IRT played an important role in MPEG video coding, as well. MPEG and DVB comprise the basis for the digital transmission of television signals. The DVB transport stream excels due to time-division multiplexing, high reliability, and a variable, configurable bandwidth.

By standardising the transmitted data stream's syntax, MPEG also standardises the decoder's functionality. The potential of MPEG is, particularly in the realm of video coding, practically limitless. Very large images can be coded at very high data rates, for example. And variously complex algorithms can be used for coding and decoding. Since this can result in remarkably different structures in coders and decoders, however, the MPEG standard defines restrictions not only for permissible parameters such as picture size and bit rates (levels), but also for the complexity of algorithms (profiles). For DVB use, only MP @ ML (Main Profile at Main Level) is currently permissible.

Principal Parameters are:

Profiles
- 4:2:0 chroma sampling
- no bi-directional prediction
- no scalability

Levels
- number of active pixels per line: 720
- number of active lines per frame: 576
- frame rate: 30 Hz
- bit rate: 15 Mbit/s

MPEG provides two different multiplexing types. First, the programme stream primarily serves to combine all of a programme’s components (e.g. audio, video), and to transfer or store data on error-free media such as CDs or other disks. Second, the transport stream is solely for the digital transfer of video.

The Main Characteristics of a Transport Stream include: