Input File Properties
With the exception of the framerate of our main feature, all the important properties of our source files have been homogenized so they're the same. The resolution of each file is 720x480, which is NTSC Full D1. The colorspace used is YUY2 with ITU-R BT.601 colorimetry. All files consist of original film frames.
DCT Precision
As we determined with Bitrate Viewer in the last guide, The 39 Steps, Electrical Earthquake, Eleventh Hour, and The Mechanical Monsters have a precision of 8, The Mummy Strkes and all the trailers have a precision of 10, and all other MPEG-2 files have a precision of 9.
MPEG File Requirements
Since our MPEG-2 files must be ready to be video assets for our DVD, we need to start with the DVD-Video specifications for guidance. Additionally, since we've prioritized our titles in groups we'll be using three different settings. Applying the same settings to multiple files is easy to do with CCE by taking advantage of the program's Template feature. By creating templates ahead of time we can quickly create a job to encode all our video.
DVD Requirements
The encoding requirements we need to consider are resolution, aspect ratio, framerate, bitrate, frame type, DCT Precision, and GOP Structure. Our source files (as processed by our AviSynth scripts) already have the correct resolution and are all progressive. Framerates are 23.976fps and 25fps. Although only one is standard for film content destined for NTSC DVDs, both will work with the proper pulldown flags added. This will happen after CCE encodes the MPEG video files, and will require a different tool called DGPulldown. Since our video is progressive, we'll need to make sure the scan order is zigzag and aspect ratio for all our video should be set to 1.33 (4:3). Although the AR for some of our cartoons started out at 1.36 instead, simply telling CCE to set it to 4:3 will bring it into compliance.
DCT Precision
DCT precision for re-encoding MPEG-2 files should be set to match the source. For our MPEG-4 video we'll use a precision of 10, which is the highest allowed for DVD-Video. This will also complicate template creation somewhat, as three different values will be used for different cartoons.
GOP Structure
A good rule of thumb to start with is two GOPs per second of video for DVD-Video. For NTSC DVD's the technical limit is 18 frames per GOP. For our files, with framerates of 23.976fps and 25fps we can use a 12 frame GOP. It's standard for DVD to have a single I frame per GOP and two B frames for each I or P frame. This will give us a pattern of IBBPBBPBBPBB for our encoder to use.
Bitrate
In order to make the most out of the space we have available on our DVD we'll be using variable bitrate (VBR) encoding. This allocates more bits to some frames and less to others in an attempt to give every frame the same quality. In reality, some frames are so complex that quality will suffer no matter what, but VBR will minimize that as much as possible. In the last step we came up with bitrates of 6,597kbps for the main feature, 4,556kbps for cartoons, and 3,427kbps for trailers. These will be our average bitrates. The resulting files will be the same size as if we encoded them at a constant bitrate (CBR) using those same values. The maximum video bitrate allowed for DVD-Video is 9,800kbps or 10,080kbps for the total mux_rate (video + audio), whichever is less. Since I don't like encoding above 9,000kbps for burned discs and the audio for each title is 2 channel AC-3 at only 192kbps, I feel safe setting the maximum bitrate at 9,000kbps for every file. The minimum is a debatable figure, and can vary from file to file. You can set it to 0 sometimes with no ill effects, but this will occasionally cause problems, so I normally set it to 500kbps.
