User’s Manual v.15
QVidium
®
H.264 HD Video Codecs
™
Copyright 2011-2014 QVidium
®
Technologies, Inc.
Page 19 of 71
and HD vs. SD). You can also use the advanced encoding parameters (Section 3.6) to scale the
video resolution and frame-rate.
The QVPRO/QVENC can output the encoded video stream either as a
Constant Bit Rate
(CBR)
IP stream, a Capped Variable Bit Rate (
Capped VBR
) IP stream, or a Low-Delay Variable Bit
Rate (
Low Delay VBR
) IP stream. The default is to output a CBR stream to maintain the highest
level of interoperability with third-party decoders, but you can change this under the
Advanced
Encoding
profile. In all cases, you need to enter a desired
Stream Bit Rate
in the
Basic
Encoding
profile. For CBR mode, the output stream will include about a 3% overhead of NULL
packets to pad the stream in order to keep the output bit rate constant and at the selected value.
For Capped VBR and Low Delay VBR, the Stream Bit Rate sets the maximum output bit rate, and
the encoder only uses the amount of bandwidth that it needs to encode the video content. For
either any of these three
Stream Modes
, the QVPRO and QVENC will automatically set an
internal Video Bit Rate by subtracting from this value the
Audio Bit Rate
you select, and about
10% for IP packetization overhead (if IP output is selected). A VBR stream has the advantage of
optimizing IP network efficiency by eliminating unnecessary null packets from the media stream.
In general, the video rate may be less than this rate, depending upon video content. Thus, a VBR
stream can have large variations in bit rate, but will produce a much lower average bit rate than
CBR.
QVidium has implemented a precision packet output control and metering mechanism, called
Pacing
(under the
Advanced Networking
encoder profile), that regulates the output timing of the
IP packets to maintain a constant inter-packet spacing, thereby minimizing packet jitter to under
25ms. This helps to reduce packet loss on Internet links that limit packet bursts. It also helps with
interoperability with older decoders that have very limited input buffers. This feature is on by
default, but it can add ¾ second of latency or more to the stream. If low latency is required, then
you can select the
Low Delay VBR
for the Stream Mode, which uses a different mechanism to
minimize packet jitter.
Note:
Be aware that the user interface will not warn you if you try to enter a bit rate beyond the
operating limits of the codec. For more details on the range of
MPEG encoding bit rates
, please
see
Appendix C
(Section 13.3). For more information on the various
video parameters
(Frame
Rate, Encoding, Format, Resolution, etc.) please
see
Appendix A
(Section 13.1). For HD or SD
video, you can select either MPEG2 or MPEG4-AVC (H.264)
Video Encoding
.
Warning:
By default, the SDI or HDMI video input expects to see embedded audio for the encoder
to start. To encode a stream without embedded audio, please check
Video Only
for the
Audio/Video
parameter in the Advanced tab. You can also encode only audio by setting this
parameter to
Audio Only
. For the QVENC, you also have the option of using the analog external
audio inputs for the audio source to embed into the output stream.
3.3 Basic Encoding Configuration
All the basic parameters you normally would need to set when creating a new encoding profile are
grouped together under the
Basic
tab of the
Encoder Profile
, as shown in Figure 1a. We strongly
recommend not changing any of the advanced encoder parameters unless you have carefully read
this manual and you are confident of what you are doing. If you have problems with the encoder,
we suggest reverting to the default advanced encoding parameters (by highlighting the profile you
are using and clicking
Default
from the Profile panel).
