A contribution codec is the high-quality, low-loss codec used to move audio between production stages — from a venue to a studio, between facilities, into the cloud — before the final delivery encode. Its priorities differ from a delivery codec's: it must survive repeated decode/re-encode cycles (cascading) without accumulating audible artefacts, because contribution audio is typically processed and re-encoded several times before it reaches the audience. That favours lossless or very lightly compressed, robust codecs at generous bitrates, sometimes with extra error protection for the link. Only at the last step is the audio compressed hard with an efficient delivery codec like AAC or E-AC-3. Using a lossy delivery codec for contribution is how quality quietly bleeds away across a chain.
