Multiple description coding: Difference between revisions

Revision as of 12:44, 7 January 2015

Revision as of 08:57, 26 January 2015

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MDC is a form of data partitioning, thus comparable to layered coding as it is used in [[MPEG-2]] and [[MPEG-4]]. Yet, in contrast to MDC, layered coding mechanisms generate a base layer and n enhancement layers. The base layer is necessary for the media stream to be decoded, enhancement layers are applied to improve stream quality. However, the first enhancement layer depends on the base layer and each enhancement layer ''n'' + 1 depends on its subordinate layer ''n'', thus can only be applied if ''n'' was already applied. Hence, media streams using the layered approach are interrupted whenever the base layer is missing and, as a consequence, the data of the respective enhancement layers is rendered useless. The same applies for missing enhancement layers. In general, this implies that in lossy networks the quality of a media stream is not proportional to the amount of correctly received data.

Besides increased fault tolerance, MDC allows for rate-adaptive streaming: Content providers send all descriptions of a stream without paying attention to the download limitations of clients. Receivers that can'tcannot sustain the data rate only subscribe to a subset of these streams, thus freeing the content provider from sending additional streams at lower data rates.

The vast majority of state-of-the art [[codec]]s uses single description (SD) video coding. This approach does not partition any data at all. Despite the aforementioned advantages of MDC, SD codecs are still predominant. The reasons are probably the comparingly high complexity of codec development, the loss of some compression efficiency as well as the caused transmission overhead.