Because MPEG encodes both the video and audio portions of a file into a single track, encoding MPEG files as FLV files might result in the audio portion being removed. This occurs primarily when encoding video files into FLV format on Mac OS. On Mac OS, MPEG video is imported using QuickTime. QuickTime does not support extracting audio content from MPEG files (although QuickTime correctly plays back an MPEG file with audio programming).

If you are encoding MPEG video with audio on a Macintosh computer, it is recommended that you first convert the MPEG video clip into another format that encodes audio and video as separate tracks within the file. You can then encode the other format as an FLV file, and preserve the audio content.

An alternative is to use a computer with the Windows operating system. Windows imports MPEG video using DirectShow, which supports extracting both the video and audio tracks of an MPEG file. This lets you convert MPEG video to the FLV format without removing the audio portion of the video clip.