Error Resilience

Streaming compressed video over communication channels that introduce errors, losses and excessive delay requires countermeasures to preserve the quality of the viewing experience.

We refer to the ability of the system to minimize and to quickly recover from the damage as its robustness. VSofts achieves robustness through two separate and complementary techniques: error resilience and error concealment.

Error resilience refers to mechanisms in the encoder that enhance the ability of the compressed bitstream to resist channel errors. Error resilience functionality in the encoder produces a bitstream that supports error recovery at the decoder.

The following methods are used in VSofts encoders:

• Selective intra coding (including intra macroblocks update based on motion tracking, row based distribution, random distribution)
• Frame segmentation into slices
• Constrained texture prediction
• Flexible Macroblock Order (FMO)

Error concealment refers to the actions taken by the decoder to analyze losses and conceal them in the displayed video by minimizing the visual artifacts. The concealment schemes can be spatial, temporal or combined. In spatial interpolation, the values of missing pixels are estimated from the surrounding pixels of the same frame, without using the temporal information. Temporal interpolation is based on the corresponding regions of the reference frames. If a motion vector is missing, it can be estimated based on the motion vectors of the surrounding regions. Combination schemes use an adaptive mechanism to choose the best concealment method for each lost macroblock.

VSofts decoders use the following methods:

• Spatial texture interpolation
• Motion compensation
• Severe loss compensation