Computer movie files/Video/Mod16
When talking about video resolutions, mod16 means that the resolution (both horizontally and vertically) can be divided by 16 with no remainder. For example, 640/16 = 40, which means it is a mod16 resolution. 650/16 = 40.625, which means it is not a mod16 resolution.
Why is it important to have a mod16 resolution?
Most video formats, including all MPEG-4 video formats divide the image up into blocks of 16x16 and then encode these blocks. What this means is if your video is not mod16, the codec will end up with some blocks that extend off the edge of the image. This is bad for two reasons:
- The codec must invent data to fit in there, which it must encode, therefore lowering overall quality of the rest of the video, and
- Some video decoders do not decode non-mod16 videos correctly, and leave green or white stripes along the sides of the video on playback.
For these reasons you should always attempt to encode to mod16 resolution.
When it might not be a good idea to encode to mod16
- When you are using a very small resolution and need to keep an accurate aspect ratio. If you are encoding a 16:9 video to 240x___, the nearest mod16 resolution is 128, which is around 5% off the technically correct value. Even a 5% aspect error is reasonably low though.
- When you need to keep an exact aspect ratio.
- When your video comes as a non-mod16 format and you don't want to resize at all.