Digital broadcasting systems, for example digital multimedia broadcasting (DMB) and digital video broadcasting (DVB) systems, are nowadays widely used. Such digital broadcasting systems may provide information and entertainment at home, while a user is travelling by car, train or ship, or while a user is walking around. In digital broadcasting systems, the video streams may be transmitted wirelessly and may pass through a radio frequency channel from a sender to a receiver. The radio frequency signals may be disturbed by environmental influences and may have a varying quality and may support varying transmission rates depending on the transmission distance and transmission environment. Poor reception quality as may have various reasons, including without limitation weather conditions, poor coverage of a radio communication network in certain regions such as tunnels, or interference with other radio sources.
The video data may be corrupted when the radio signals are disturbed. Various correction techniques, such as forward error correction (FEC) may be used to at least partially correct some of the errors, such as syntax errors. Nevertheless, there may be artifacts when the video data is processed and the video is output through an optical output device, such as a display screen or a video projector. Examples for artifacts include spatial artifacts or temporal artifacts. Examples for spatial artifacts include blocking, blurring or ringing.
Temporal artifacts include artifacts which can be seen only during video playback, such as flickering or jerkiness. Freezing is one of the most severe perceptual temporal artifacts. Freezing can be caused when a signal is not available or has been lost for a time-span. Freezing may also occur when the signal quality is so low that it is preferred to freeze the video on the last best received frame rather than showing a video of poor quality. Freezing is among the artifacts which are considered to most severely affect the perceived quality of a video.