MPEG files are often multiplexed or "muxed" which means that the audio and video are combined into one data stream. Useful for optical disc formats, not so useful for editing and such.
Your file is most likely in this form. Use MPEG Streamclip to extract the file to something suitable for editing, i.e. ProRes, DV, DVCProHD or whatever you have available. Here the audio and video files are separate streams or tracks combined into one media package.
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Sleeplings, AWAKE!