It would make sense that there’s a bottleneck but based on the activity with the CPU and GPU it seem that they’re not the cause of the bottleneck. I’m almost completely sure it’s the HDD since it’s a general 3.5′ Western Digital SATA II 3Gbps HDD.
But I seem to be having this same problem with rendering .wmv videos even after I’ve converted the uncompressed avi file to mp4 which seemed to work when I rendered it into mp4 format instead of wmv