FLV is a video format: it packages Sorenson Spark or VP6 video in Adobe's Flash container, now largely obsolete following the end of Flash Player support. MP3 is a audio format that applies psychoacoustic lossy compression to remove frequencies the human ear perceives least, producing small files at acceptable audio quality. 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 MP3 natively or when the target platform only accepts MP3. 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.