QVidium QVMP2C-1011 - Manual (Page 33)

User’s Manual v.28 QVidium™ MPEG2+4 Codec
33 of 45 - Copyright 2007-2008 QVidium™ Technologies, Inc.
Audio Sampling Rate (Hz): The audio sampling rate specifies the clock rate for capturing
and digitizing the incoming analog audio signal. Because of anti-aliasing filtering, the
maximum audio frequency that can be digitized is limited to a frequency of about 1/3 to
1/2 of the audio sampling rate. Internal anti-aliasing filters severely attenuate audio
signals above a frequency of about 1/3 of the sampling rate. Thus, for a standard music
CD rate of 44.1 KHz, the maximum audio frequency that the encoder can pass is about
14.7 KHz. The valid selectable audio sampling clock rates are 22.05 KHz, 32 KHz, 44.1
KHz, and 48 KHz.
Video Frame Rate (Full Frame Rate and fractions thereof): Select Full Frame Rate for
normal video. This will encode the video signal at 29.97 frames per second for NTSC and
25 fps for PAL video format. If you need to produce lower video bitrates, and reducing the
resolution is not sufficient or undesired, you can use this feature to sacrifice frame rate for
lower bitrates. However, to use thus feature you must select MPEG-4SP encoding and
Program Stream transport.
By reducing the frame rate, you can reduce the stream bitrate to a minimum value of 143
Kbps. In general, reducing the frame rate also reduces the required video bitrate by the
same factor. You can select factors of one-half (1/2), one-third (1/3) and other fractions
down to one-sixth (1/6) of the standard NTSC or PAL frame rate. However in any case,
the minimum allowable stream bitrate has a lower limit of 143 Kbps.
Video Encoding: The MPEG2+4 IP Codec digitizes an analog composite or S-Video
signal according to the ITU-R.BT-656 standard, performs a 4:2:2 to 4:2:0 conversion and
compresses the digitized video using either the MPEG-2 video encoding standard
(MP@ML, ISO/IEC-13818-2) or MPEG-4 simple profile (SP @ L1, L2, & L3 with
extensions for D1 and interlacing, ISO/IEC 14496-2) compression as selected. MPEG-2
generally produces better quality video compression at video bitrates above 2.5 Mbps.
MPEG-2 produces I, P, and B-Frames and will always produce a constant 29.97 (or 25.0)
fps frame rate.
We suggest that you select MPEG-4 compression at lower bitrates (especially 1.5 Mbps
and lower). With MPEG-4, you can also select lower frame rates and it also includes a
number of newer encoding techniques and degrees of freedom in compressing the video
that are not available for MPEG-2. However, the MPEG-4 compression of the MPEG2+4
IP Codec is Simple Profile (Part 2 of the ISO MPEG-4 standard), meaning that it will not
produce B-Frames (Bi-directional interpolated prediction frames), which is a
disadvantage compared with MPEG-2 main profile encoding.
Video Format: This allows selection between the NTSC standard as used in North
America and Japan and the PAL video format used in Europe. The video format specifies
both a set of permissible video resolutions and a video frame rate. NTSC captures
interlaced video at 29.97 frames per second, while PAL captures interlaced video at 25
frames per second.
Video Resolution (NTSC and PAL): The video resolution for Standard Definition video
(D-1 resolution) is 720x480 pixels for NTSC resolution (480i) and 720x576 pixels for PAL
video format (576i). This is the resolution commonly used for DVDs and Standard