Layered coding is a type of data compression for digital video or digital audio where the result of compressing the source video data is not just one compressed data stream, as in other types of compression, but multiple streams, called layers, allowing decompression even if some layers are missing.
This is in contrast to other types of compression, where the result is typically a single data stream.
During decompression, all layers can be combined to recreate the original video stream.
If layers are missing, the resulting stream will have reduced visual quality, but will still be usable.
[2] However, with multiple description coding the different streams are independent of each other, so any subset can be decoded, providing additional flexibility.