QVidium MPEG2+4 Codec

Encoder: Explanation of Settings and Operation

 

Encoding Parameters

This section covers parameters related to the analog input signals and encoding settings.

 

Stream Type: This allows selection between Transport Streams and Program Streams. Generally Transport Streams should be selected, but for bitrates under 1 Mbps, the Program Stream type works better. Program Streams allow variable bitrate encoding for better quality at low bitrates.

 

Stream Bit Rate: Total constant bit rate for aggregate multiplexed multimedia stream. The transport stream bit rate includes the video program, audio program and program stream information. The encoder automatically sets the video encoding bit rate taling into account the transport stream rate minus the audio and program stream information rates. See BitrateLimits.html for more information on maximum and minimum bitrates. The higher the bit rate, the better the video quality.

 

Audio Bit Rate (compressed): The audio bit rate determines encoding audio quality and can be set to one of 64,000, 128,000, 192,000, 256,000 or 384,000 bits per second. To disable and not send audio, set this rate to 0. Audio is compressed using MPEG-1 Layer II encoding. Higher bit rates provide higher quality audio.

 

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 32 KHz, 44.1 KHz, and 48 KHz.

 

Video Encoding: The MPEG2+4 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) or MPEG-4 simple profile ( ISO/IEC 14496-2) compression as selected.

 

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): The user can select from among 5 standard video resolutions used with NTSC video: 720x480, 704x480, 640x480, 480x480, 352x480, 352x240, and 320x240. All resolutions are specified as horizontal pixels x vertical pixels. The two resolutions, 320x240 and 640x480 are for use with computer displays and other devices that display square pixels.

 

Video Resolution (PAL): The selectable PAL resolutions are: 720x576, 704x576, 352x288 (horizontal x vertical pixels).

 

Video Input: This selects between the composite video, S-Video input, cable television (CATV) and Over-The-Air United States (OTA-US) inputs.

 

TV Channel: The MPEG2+4 Codec can encode video directly from a cable system. This specifies the specific cable channel to tune into and encode when the video input is set to CATV or OTA-US.

 

Network Parameters

The fields below relate to Ethernet/IP video transport settings.

 

IP Transport: This selects the type of video IP packet encapsulation and error correction used by the codec in generating a Video/IP stream. All packetized video transport mechanisms encapsulate a multiplexed constant bit rate MPEG-2 transport stream.

 

 

Destination IP Address or Hostname: This specifies the IP address or Hostname for the Video/IP stream.

 

UDP Port: This specifies the UDP port number, base 10, for the Video/IP stream.

 

TS packets per IP packet: This field allows specification of the number of 188-byte MPEG-2 Transport Stream packets per IP packet. The standard MTU for Ethernet packets permits a maximum of 7 TS packets per IP packets, which is the default.

 

Unicast TTL (Time-To-Live): This sets the IP packet’s Time-To-Live field for unicast data streams and thereby limits the number of intermediate IP router hops that each unicast IP packet can travel before being dropped by a router. (A unicast packet is a packet destined to travel to a single IP address.)

 

Multicast TTL (Time-To-Live): This sets the IP packet’s Time-To-Live field for multicast data streams and thereby limits the number of intermediate IP router hops that each multicast IP packet can travel before being dropped by a router.

 

TOS (Type-of-Service): The TOS (Type-of-Service) field in an IP packet specifies the packet priority and type of differentiated services requested by the packet to each router at each hop to a destination. Although setting this field will directly set the TOS byte field in the IP packets for the output video stream, routers along the way may not necessarily recognize or comply with this request.

 

 

ProMPEG FEC

The parameters below ONLY pertain to ProMPEG forward error correction. They will be ignored when ProMPEG IP Transport is not selected.

 

Columns: This sets the number of columns in the two-dimensional packet interleave matrix used by ProMPEG Release 3 FEC to generate column parity checksum packets. The larger this number, the larger a contiguous burst packet drop that the FEC can handle will be. However, increasing the number of columns increases the transport latency.

 

Rows: This sets the number of rows, R, in the two-dimensional packet interleave matrix. It thereby sets the FEC overhead, since one FEC packet is generated for each R rows. Thus, column-only FEC will add an additional 100/R percent to the baseline transport stream bit rate without FEC.  

 

In ProMPEG Release 3.2 FEC, a row parity packet can be generated along each row of the interleave matrix. Thus for a matrix having C columns, one row parity packet would be generated for each C columns. This can add an additional 100/C percent overhead to the transport stream bit rate for when enabled. However, these row checksum packets will NOT be generated UNLESS “FEC Type” (below) is "Row and Column" FEC.

 

FEC Type: This allows selection between "Column Only" FEC and "Row and Column" FEC. Normally, FEC without row parity can be effective in reconstructing isolated single and burst packet losses. However, should the packet loss patterns become more frequent and occur at intervals less than the total (row x column) number of packets held in the interleave array, then column-only FEC will not be completely effective in recovering lost packets. The addition of row FEC increases the ability to recover lost packets when the losses start to occur in shorter intervals.

 

ARQ Error Correction

The parameters below ONLY pertain to ARQ error correction. They will be ignored when ARQ IP Transport is not selected.

 

ARQ Port: This sets the port that the encoder listens on to receive ARQ retransmission requests from the decoder. If you have a firewall, please be certain to open this port when using ARQ error correction. This setting MUST match the corresponding setting on the decoder.