I have a AVI file I need to convert to MPEG-4. The file is 15 minutes +/-. When I try to convert in MPEG Streamclip it only converts 1 minute 28 seconds out of the 15. At the bottom of the Streamclip screen it shows trimming to 1:28 minutes. How do I turn trimming off so that I convert the total clip length of 15 minutes?