It's probably crashing because the video needs more bitrate than 700mb filesize allows.
Avidemux works best with either constant quantize or 2-pass. For MPEG, I prefer 2-pass. It's not always smart at the best bitrates for MPEG-2. But for x264, I prefer the constant quantize.
For advanced x264, Hybrid is really nice.
I'm looking to create a guide for all of those. The
Avidemux guides already exist, but simply are not linked in menus. The Hybrid guide is scheduled as soon as the site coding is done.