Transcoding is the direct digital-to-digital conversion from one (usually
lossy)
codec to another. It involves decoding/decompressing the original data to a raw intermediate format (i.e.
PCM for audio or
YUV for video), in a way that mimics standard playback of the lossy content, and then re-encoding this into the target format.
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Early system on Ferut computer. Listed in CACM 2(5):16 (May 1959).