whenever i cut a chunk from a video i cant play it for different reasons. lets say i have a video thats 10 minutes long and 100mb. if i cut a 2 minute chunk, i can view the properties of the chunk in my video folder and it says its a 20mb chunk. when i open it in totem, it says the video is 10 minutes long. the video will then start playing the chunk and freeze somewhere before the 2 minutes that its supposed to be. what gives??

ive read a few of the tutorials about using avidemux and there was one that said that when you name the chunk that you have to use the file type in the name. for example, "video.avi" as opposed to just "video". when i try that, it wont open at all in totem, i just see the totem logo on the screen. when i name the file without the extension, i get the problem i listed above. any help?