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Source Block construction FEC codes calculated over a logical ‘source block’ Source Block consists of concatenated ‘source packet information’ (SPI) for each packet in the block Arrangement of packets into blocks is out of scope Common example is based on time – source blocks all have approximately the same playout duration (“protection period”) Source Packet Information consists of UDP flow identifier (1 byte) UDP Packet Length (2 bytes) UDP Payload Padding bytes SPI always starts on an FEC Symbol Boundary within the source block (symbols can be any size, but within a source block they are all the same size) FEC framework adds/removes padding to symbol boundaries at encoder and decoder |