I provide an audio transcription service, for which I charge according to the audio length. Mostly I receive either audios or videos that have been produced by the person or organisation that sent me the material to be transcribed, so the copyright is theirs on both the source and transcript. No problem.
Sometimes, however, I get asked to transcribe material that is publically available online (e.g. podcasts or YouTube videos), and not owned by the person requesting the transcript. The transcript may or may not be for the requestor's personal use.
Is it illegal for me to transcribe this sort of material? I understand that a transcript of a podcast or video is a derivative work, and only the copyright owner can authorise creating a derivative work.