I have been doing some transcoding to convert from AVI to MP4 to achieve more compression. The source video is usually DivX/Xvid.
The video options are set to x264, 900 kbps avg bitrate, 2 pass encoding with turbo first pass. Audio is AAC with Auto option.
The question is that there is a time difference between the source and encoded video. usually the final video is smaller in size and shorter in time. is this due to the changing fps?