Dynamically changing the video encoding bitrate, 3 dynamically changing the video encoding bitrate, 1 url control – QVidium QVSD User Manual
Page 18: 2 command-line control
User‟s Manual v.3
QVidium
®
QVSD H.264 SD Video
Codec™
Copyright 2011 QVidium
®
Technologies, Inc.Page 18 of 53
The analog audio input, by default, accepts a maximum input voltage of about ±400 mV
peak
. Above
this level, the input circuitry limits any additional signal levels by clipping the digitized signal to this
peak value. This level is close to the standard consumer analog level of ±447 mV
peak
, and
significantly less than professional peak audio voltage levels (1.737 V
peak
US and 2.192 V
peak
German). In order to accommodate various consumer and professional analog audio input
sources, you can select from among 3 preset standard audio signal levels, Consumer,
Professional US, Professional Europe. You can also manually adjust the attenuation of the audio
input.
3.3 Dynamically Changing the Video Encoding Bitrate
Once encoding has begun, you can instantaneously vary the video encoding bitrate. This can be
useful when connecting to wireless modems and other network connections with limited, but
unpredictable, time-varying throughput characteristics. As described in this section, we provide
several mechanisms for dynamically adjusting the video encoding bitrate. In particular, this can
allow a modem to feed back link throughput constraints directly to the encoder to dynamically
optimize video quality over such bandwidth-constrained networking links.
3.3.1 URL Control
There are 2 URLs, one to get the current video bitrate and a second url to set the video bitrate.
These URLs return plain text (no HTML) to simplify parsing. The "Encoder->Bitrate" link in the
web UI allows you to set the video bitrate with a browser.
/cgi-bin/encoder_bitrate2.cgi: Gets the current video bitrate. Returns
VIDEO_BITRATE=xxxxxxx, where xxxxxxx is the current bitrate.
/cgi-bin/encoder_bitrate2.cgi?VIDEO_BITRATE=xxxxxxx: Sets the video bitrate where xxxxxxx
is the desired bitrate. Returns VIDEO_BITRATE=xxxxxxx where xxxxxxx is the bitrate that was
set. The maximum video bitrate is 25000000.
Examples of using the wget command. The initial bitrate was 23Mbps.
$ wget -q -O -
VIDEO_BITRATE=23000000
$ wget -q -O -
VIDEO_BITRATE=9000000
$ wget -q -O -
VIDEO_BITRATE=9000000
$ wget -q -O -
VIDEO_BITRATE=25000000
3.3.2 Command-line Control
The program, /qvidium/qvctrl, allows you to communicate with the encoder via a command-line
interface, such as telnet, ssh, or the RS-232 Console port. The first argument is always
/dev/qvencode, The second argument is "get_videobitrate" or "set_videobitrate xxxxxx" where
xxxxxx is the bitrate would want to set (max bitrate is 25000000). The command always returns
VIDEO_BITRATE=xxxxxxx where xxxxxx is the current bitrate. Here are examples:
[QVSD.qvidium.com]$ /qvidium/qvctrl /dev/qvencode "get_videobitrate"
VIDEO_BITRATE=4000000
[QVSD.qvidium.com]$ /qvidium/qvctrl /dev/qvencode "set_videobitrate 2000000"
VIDEO_BITRATE=2000000
[QVSD.qvidium.com]$ /qvidium/qvctrl /dev/qvencode "set_videobitrate 8000000"
VIDEO_BITRATE=8000000