Demultiplexing demux
Demultiplexing Demux Description
The opposite of multiplexing. In this process, a combined audio/video stream will be separated into the number of streams it consists of (a video stream, at least one audio stream, and a navigational stream). Every VOB encoder demultiplexes the VOB files before encoding (FlasKMPEG, MPEG-2avi, DVD2MPG, ReMPEG-2) and every DVD player does the same (audio and video are being treated by different circuits, or decoded by different filters on a PC). It is the amount of data in a particular space of time (eg. a second) - it is a property for both digital video and audio. If a video is said to have a constant data rate or constant BITRate of 150 bytes per second, it means that in every second of video, 150 bytes is used to store the video. BITRate can be constant (CBR) or variable (VBR). CBR means that the stated BITRate will be constant throughout the video, while VBR will mean that the parts of the video that needs more BITRate will get it, while parts that don't need it will have a lower BITRate.
So the act of separating these streams is called Demuxing or Demultiplexing. You can do this with MPEG 1 or 2 streams using MPEG Tools in TMPGenc.
The Demux block extracts the components of an input signal and outputs the components as separate signals. The block accepts either vector (1-D array) signals or bus signals. The Number of outputs parameter allows you to specify the number and, optionally, the dimensionality of each output port. If you do not specify the dimensionality of the outputs, the block determines the dimensionality of the outputs for you.
The Demux block operates in either vector or bus selection mode, depending on whether you have selected the Bus selection mode parameter. The two modes differ in the types of signals they accept. Vector mode accepts only a vector-like signal, that is, either a scalar (one-element array), vector (1-D array), or a column or row vector (one row or one column 2-D array). Bus selection mode accepts only the output of a Mux block or another Demux block.
The Demux block's Number of outputs parameter determines the number and dimensionality of the block's outputs, depending on the mode in which the block operates.
In vector mode, the value of the parameter can be a scalar specifying the number of outputs or a vector whose elements specify the widths of the block's output ports. The block determines the size of the block's outputs from the size of the input signal and the value of the Number of outputs parameter.
Note that you can specify the number of outputs as fewer than the number of input elements, in which case the block distributes the elements as evenly as possible over the outputs.
You can use -1 in a vector expression to indicate that the block should dynamically size the corresponding port. For example, the expression [-1, 3 -1] causes the block to output three signals in which the second signal always has three elements while the size of the first and second signals depends on the size of the input signal.
If a vector expression comprises positive values and -1 values, the block assigns as many elements as needed to the ports with positive values and distributes the remain elements as evenly as possible over the ports with -1 values. For example, suppose that the block input is seven elements wide and you specify the output as [-1, 3 -1]. In this case, the block outputs two elements on the first port, three elements on the second, and two elements on the third.
Specifying the Number of Outputs in Bus Selection Mode
The specified value must equal the number of input signals. For example, if the input bus comprises two signals and the value of this parameter is a scalar, the value must equal 2.
Vector each of whose elements specifies the number of signals to output on the corresponding port. For example, if the input bus contains five signals, you can specify the output as [3, 2], in which case the block outputs three of the input signals on one port and the other two signals on a second port.
Cell array each of whose elements is a cell array of vectors specifying the dimensions of the signals output by the corresponding port. The cell array format constrains the Demux block to accept only signals of specified dimensions. For example, the cell array {{[2 2], 3} {1}} tells the block to accept only a bus signal comprising a 2-by-2 matrix, a three-element vector, and a scalar signal. You can use the value -1 in a cell array expression to let the block determine the dimensionality of a particular output, based on the input. For example, the following diagram uses the cell array expression {{-1}, {-1,-1}} to specify the output of the left-most Demux block.
In bus selection mode, if you specify the dimensionality of an output port, i.e., specify any other value than -1, the corresponding input element must match the specified dimensionality. |
