MKV is a video format: it stores video, audio, subtitles, and chapters in an open-standard container that supports virtually every codec. M4A is a audio format that stores AAC-encoded audio in an MPEG-4 container, the standard audio format produced by iTunes and Apple devices. This extracts the audio stream from the video container, discarding the video track. The audio track is decoded and re-encoded (or stream-copied if the codec matches) while the video frames are discarded. Converting between these two formats is common when the source application does not support M4A natively or when the target platform only accepts M4A. 1converter processes this conversion server-side using open-source tools. Files are transferred over HTTPS, converted on secure cloud servers, and automatically deleted after 24 hours.