User`s manual

16 CaptionMaker for Windows
P Frames Per Key Frame– P frames are used in MPEG compression; in general, this
property does not apply to other compression formats. For example, suppose a key frame
occurs once every 10 frames, and there are three P frames per key frame. The P frames will
be spaced evenly between the key frames. The remaining six frames are bidirectional (B)
frames.
Subtitle Quality vs. Video Dimensions
The subtitle generator inside CaptionMaker generates the subtitles images at a resolution of
720x480 (NTSC). When the dimensions of the video file (width x height) are smaller than
this, for example 320x240, then the subtitles must be scaled down to match the resolution of
the video file. This results in some loss in the quality of the subtitles. The smaller the
dimensions of the video file, the more quality is lost scaling down the subtitle images. To
obtain the highest quality subtitles, the video dimensions should be 720x480 (or at least
640x480).
Time Code Restrictions
The subtitle generator inside CaptionMaker uses time code (SMPTE12M) to control the
timing of the subtitles. Therefore, the video file being subtitled needs to be 24, 25, 29.97, or
30 frames per second. Subtitling a video file with a frame rate other than these can be done,
but this can make it very difficult to achieve accurate subtitle timing.
Processing Time
We ran a few tests to caption and subtitle a 1 minute video. The computer used was running
WinXP Pro with a AMD Athlon XP 2000+ (1.6 GHz), 512 MB PC133 and 40 GB ATA 133
hard drive.
A. Captioning:
MPEG file = MPEG-2.m2v.mpeg (34.5MB, length = 1 minute 20 seconds)
Time to export captions into MPEG file = 1 minute 7 seconds
Time to import captions from MPEG file = 3 seconds
B. Subtitling:
Time to subtitle depends on selected compressor.
Video File 2 = Demo_DV_720x480.mov (289MB, length = 1 minute 20 seconds)
Time to subtitle using Microsoft RLE = 1 minute 27 seconds
Time to subtitle using Cinepak = 28 minutes