One thing that bothered me enough to comment on: "transcoding" doesn't seem like the right term in this context. "Encode/decode" is technically correct, but "compress/decompress" would have made the intent much clearer.
> Transcoding does not mean compressing everything. Images, video, and fonts are usually compressed already.
It's because they're already lossily compressed that, precisely, they're the typical targets for transcoding.
EDIT: oops, wrote lossless instead of lossy, sorry about that