Technical specifications Video CD




1 technical specifications

1.1 structure
1.2 video
1.3 audio
1.4 advantages of compression
1.5 other features
1.6 internal control





technical specifications
structure

video cds comply cd-i bridge format, , authored using tracks in cd-rom xa mode. first track of vcd in cd-rom xa mode 2 form 1, , stores metadata , menu information inside iso 9660 filesystem. track may contain other non-essential files, , shown operating systems when loading disc. track can absent vcd, still work not allow displayed in computers.


the rest of tracks in cd-rom xa mode 2 form 2 , contain video , audio multiplexed in mpeg program stream (mpeg-ps) container, cd audio tracks allowed. using mode 2 form 2 allows 800 megabytes of vcd data stored on 1 80 minute cd (versus 700 megabytes when using cd-rom mode 1). achieved sacrificing error correction redundancy present in mode 1. considered small errors in video , audio stream pass largely unnoticed. this, combined net bitrate of vcd video , audio, means 80 minutes of vcd content can stored on 80-minute cd, 74 minutes of vcd content on 74-minute cd, , on. done in part ensure compatibility existing cd drive technology, earliest 1x speed cd drives.


video

video specifications



codec: mpeg-1
resolution:

ntsc: 352x240
pal/secam: 352x288


aspect ratio:

ntsc: 4:3
pal/secam: 4:3


framerate:

ntsc: 29.97 or 23.976 frames per second
pal/secam: 25 frames per second


bitrate: 1,150 kilobits per second

rate control: constant bitrate



although many dvd video players support playback of vcds, vcd video compatible dvd-video standard if encoded @ 29.97 frames per second or 25 frames per second.


the 352x240 , 352x288 (or sif) resolutions chosen because half horizontal , vertical resolution of ntsc video, , half horizontal resolution of pal (the vertical resolution of pal being half of 576 active lines). approximately half resolution of analog vhs tape ~330 horizontal , 480 vertical (ntsc) or 330x576 (pal).


audio

audio specifications



codec: mpeg-1 audio layer ii
sample frequency: 44,100 hertz (44.1 khz)
output: dual channel or stereo
bitrate: 224 kilobits per second

rate control: constant bitrate



as cd-based formats, vcd audio incompatible dvd-video standard due difference in sampling frequency; dvds require 48 khz, whereas vcds use 44.1 khz.


advantages of compression

by compressing both video , audio streams, vcd able hold 74 minutes of picture , sound information, same duration standard 74 minute audio cd. mpeg-1 compression used records differences between successive video frames, rather write out each frame individually. similarly, audio frequency range limited sounds heard human ear.


other features

playback control (pbc) added in vcd 2.0 requires special return button


the vcd standard features option of dvd-quality still images/slide shows audio, @ resolutions of 704x480 (ntsc) or 704x576 (pal/secam). version 2.0 adds playback control (pbc), featuring simple menu dvd-video.


internal control

an example of software control chart (taken flower , snake disc 1 of 3) including menu commands found in configuration volume cdi_vcd.cfg



controls=all
curcol=yellow
psdcurcol=red
psdcurshape=arrow
initlang=dat
subttype=overlayed
subttcol=ebebeb
substcol=101010
subtbcol=0
subtacol=999999
centrtrack=2
autoplay=auto_on
dualchan=dual_on
timecode_x=64
timecode_y=100
lotid_x=64
lotid_y=64
album=standard




^ http://www.mplayerhq.hu/docs/html/en/vcd.html vcd playback
^ mpeg1 specifications . icdia.co.uk. 






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