Multiplexer, demultiplexer and transcoder

These types do not go out to the network: they link the streams of one node to each other. The multiplexer assembles a multiplex out of SPTS streams, the demultiplexer extracts a single program from a multiplex, the transcoder connects a source stream with a result stream. The test stream generator is placed here as well — it too works without an external source.

Multiplexer (muxer)

The type works from both sides: a muxer input on an MPTS stream defines the multiplex itself, while a muxer output on an SPTS stream attaches that program to the multiplex (Multiplexer). An MPTS stream can have only one muxer input, and such a stream has no other inputs.

Input: the multiplex parameters

Field	Purpose	Values
Automatic PID mapping	Enabled — every program receives its own PID window assigned by the node. Disabled — the programs keep their original PIDs, and they can be changed only by remapping on the output of the program (PID mapping). Disabling it is needed where the receivers do not re-read the PMT and have to survive a move to a new node without being reconfigured.	enabled by default
Transport stream id	transport_stream_id in the PAT, SDT and NIT tables. Together with “Network id” it forms the pair by which a receiver recognizes the multiplex; changing the pair is, for a receiver, equivalent to the appearance of a new transport (Multiplex parameters).	0–65535, default 1
Network id	network_id in the NIT and original_network_id in the SDT.	0–65535, default 1
Network name	The name of the network in the NIT — what a receiver shows during a channel search. The value is converted into the DVB encoding, so Cyrillic is displayed correctly. An empty field — the descriptor is not transmitted.	empty by default
Country code (ISO 3166 alpha-3)	The three-letter country code. It goes into the local time descriptor and, more importantly, determines which flag is placed before the channel numbers in the NIT: strict receivers take a channel number into account only with the appropriate flag.	three letters of an ISO 3166-1 alpha-3 code, empty by default
Output bitrate (kbps)	The rate of the output multiplex. A value greater than zero enables bitrate levelling: the stream goes at exactly this rate, the shortfall is padded with NULL packets and the PCR marks are recalculated. If the programs together exceed the set rate, the excess packets are dropped — the total bitrate is watched in the multiplex table (Per-program analysis). Zero is the legacy mode without levelling.	default 20000
SDT provider name	The name of the service provider in the SDT. The value is common to the whole multiplex — an individual program does not have a name of its own.	up to 251 bytes, empty by default

The editor of the multiplex composition opens from this same window — the “Edit programs…” button (Programs). It receives the automatic PID mapping value that currently stands in the window, even if it has not been saved yet.

Output: attaching a program to the multiplex

Field	Purpose	Values
Target MPTS stream	The multiplex this stream is fed into. Chosen from the list of the node’s MPTS streams. A required field; when there are no MPTS streams the list is empty and the window reports “There are no target MPTS streams — create an MPTS stream first.”	the list of the node’s MPTS streams
SDT service name (empty = stream name)	The name of the service in the SDT of the multiplex — what a receiver shows as the channel name. Contrary to the caption, an empty field does not substitute the stream name: the program gets a name of the form Channel<number>, where the number is its place in the multiplex in ascending PNR order. Adding a program with a lower PNR shifts these names for the others, so the channel name is set explicitly.	up to 251 bytes, empty by default
PNR (0 = stream id)	The program number (service_id) in the multiplex. Zero means “take the stream identifier”. Two outputs with the same number cannot be attached to one multiplex.	0–65535, default 0
Logical channel number (0 = PNR)	The logical channel number in the NIT — the position of the channel in the receiver’s list. Zero means “take the program number”. While the output or its stream is paused, the channel is marked as hidden and disappears from the receiver’s list.	0–999, default 0
Service type (0 = auto, ETSI)	The service type in the SDT and the NIT. Zero — determine it automatically from the composition of the program; another value sets the type according to ETSI EN 300 468 by hand.	0–255, default 0
PMT PID (0 = source)	The PID of this program’s PMT table in the multiplex. Zero — assign it by the general rule (the automatic program window, or, when automatic mapping is off, the original PID). The values 1–31 are reserved and are rejected.	0 or 32–8190, default 0

On the MPEG-TS PID tab of this output the remapping of the program’s PIDs inside the multiplex is set (PID mapping); the PID accept and reject lists are not configured on an output — they exist only on inputs. The order of the programs in the multiplex tables is set not here but by dragging the rows in the “Programs” window.

Demultiplexer (demuxer)

An input of an SPTS stream that extracts a single program from a multiplex or from a DVB adapter (Demultiplexer).

Input

Field	Purpose	Values
Source kind	Where the multiplex comes from: an MPTS stream of this node or a DVB adapter (DVB receiver). The choice determines the contents of the next field.	SPTS stream (default), DVB adapter
Source id	The source itself — chosen from the list of the node’s configured MPTS streams or adapters. A required field; if there are no sources of the chosen kind, the list is empty.	the list of the node’s sources
PNR	The program number. For a source of the SPTS stream kind, if it is running and has already been analysed, the number is chosen from the list of the services found, with their names; for a DVB adapter no list is offered — the number is always entered by hand. For internal T2-MI multiplexes a composite number is entered (T2-MI decapsulation).	a program number of the source

Transcoder (transcoder)

The transcoder also works from both sides: a transcoder output on the source stream is the decoder, a transcoder input on the result stream is the encoder attached to that decoder. The connection scheme and the capabilities of the backends are described in Transcoders.

Output: the decoder

Field	Purpose	Values
Transcoder backend	The processing method: without re-encoding the video, in software on the processor or in hardware on a GPU (Backends and codecs). The chosen backend must be installed on the node, otherwise the output will not be saved — including the pass-through mode, which is performed by the software transcoder (Transcoders).	Video pass-through, Software (CPU) (default), NVidia (GPU), Intel VPL (GPU)
GPU device selector	The device on a node with several cards. The list is filled with the devices of the chosen backend; the software and pass-through modes have no devices, and the list is disabled. For the NVIDIA backend an empty value means the first device, for Intel VPL the device has to be chosen explicitly — otherwise the output will not be saved.	the list of the node’s devices
Watchdog timeout (s)	After how many seconds of silence the transcoder process is considered hung and is restarted.	from 1; default 10, the creation form fills in 5
Fix PAR (N/D), Fix framerate (N/D)	The pixel aspect ratio and the frame rate as a fraction — hints for a source that does not report them or reports them incorrectly (Decoder settings).	a fraction of the form 16/9, 25/1; empty by default
Convert to BT.709	Conversion of the SD colour space to BT.709.	disabled by default

Input: the encoder

Field	Purpose	Values
Decoder	The decoder the encoder is attached to: chosen from the list of the node’s transcoder outputs with the names of their streams — paused ones are in the list too. A required field; the decoder of the same stream cannot be attached to. While the node has no transcoder output at all, the list is empty.	the list of the node’s decoders
Encoder	The codec of the output video. The list is limited by the capabilities of the chosen decoder’s backend: MPEG-2 — software and Intel, HEVC — NVIDIA and Intel, H.264 — everywhere.	MPEG-2, H.264 (default), HEVC
Video profile (H.264)	The H.264 profile. For the other codecs the field is disabled.	Main, High (default)
Video bitrate (kbps)	The video bitrate; the encoding is always CBR. It also sets the order of the variants when several encoders are attached to one decoder.	from 100, default 5000
Speed preset	The trade-off between encoding speed and quality: lower means better quality and a higher load.	1–7, default 4
Resize, Width, Height	The picture size. This is a single linked control: either a ready-made mode is chosen (reduction by 2 or 4, conversion to SD, upscaling SD to HD), or the mode of setting the width or the height — then the corresponding field becomes available and the other side is recalculated from the source proportions (Encoder settings). An arbitrary width × height pair cannot be set.	None (default), /2, /4, SD, SD PAL, SD NTSC, SD->HD
Deinterlace	Conversion of interlaced video to progressive.	enabled by default
GOP interval	The distance between key frames, in frames.	from 1, default 25
B-frames	The number of B-frames between reference frames. Default leaves the choice to the encoder, Off disables them altogether (the lowest latency, the worst compression).	Default (default), Off, 1–8
Lookahead	How many frames ahead the rate control looks. More means a better distribution of bits, but a higher latency and memory consumption.	from 0, default 0
MPEG audio rule, AAC audio rule, AC-3 audio rule	What to do with the audio track of each source codec: leave it as it is, re-encode it into the named codec or remove it (Skip). The default values leave the track unchanged (Audio processing).	MPEG, AAC, AC-3, Skip — the set depends on the source codec
Audio bitrate (kbps)	The bitrate of the re-encoded audio tracks. It does not apply to the tracks that pass through unchanged.	from 1, default 128
5.1 downmix volume	The volume of the 5.1-to-stereo downmix. Plain summing of the channels sounds quieter than the original, so the default value is greater than one.	from 0, default 1.6
Encoder PMT PID	The PID of the PMT table of the stream the encoder produces. Zero — as in the input stream.	0 or 32–8190, default 0
Encoder options (k=v:k=v)	Additional parameters of the software encoder. The field is available only with the software backend.	empty by default
PAT/PMT interval (90kHz)	The repetition period of the PAT and PMT tables in 90 kHz ticks: 9000 is 100 ms.	from 1, default 9000
Framerate resample	Halving or quartering the frame rate — for the lower variants of an adaptive set.	None (default), /2, /4

When the decoder works in “Video pass-through” mode, the encoding settings disappear from the window: what remains is the choice of decoder, the “PAT/PMT interval (90kHz)” field and the common input fields. The video is not re-encoded, and this field is not applied in pass-through mode either. The audio processing rules, on the other hand, keep working exactly as they were saved — there is simply nowhere to look at them while the decoder is pass-through; the audio bitrate and the downmix volume are not carried over in pass-through mode, and the audio is re-encoded with the default settings.

Test generator (test-stream)

An input of an SPTS stream that produces a test pattern and an audio signal without an external source (Test streams). Requires the software transcoding package to be installed.

Input

Field	Purpose	Values
Video encoder	The codec of the generated video.	MPEG-2, H.264 (default), HEVC
Video bitrate (kbps)	The bitrate of the generated video — the main lever of the load on the processor and the link.	from 100, default 3000
Width, Height	The picture size in pixels.	from 64, default 1920 and 1080
Width PAR, Height PAR	The pixel aspect ratio declared in the stream.	from 1, default 1
Frame rate	The frame rate.	from 1, default 25
GOP interval	The distance between key frames, in frames.	from 1, default 25
Video pattern	The kind of test pattern: colour bars, noise, a flat fill, a checkerboard, a moving ball and others. A moving picture is convenient for spotting freezes, a static one for spotting artefacts.	26 variants, default SMPTE 100% color bars
Audio encoder	The codec of the generated audio.	MPEG-1 Layer 2 (default), AAC
Audio waveform	The kind of audio signal: a tone, noise, silence, periodic ticks. Ticks are the default — a gap in the audio is heard on them immediately.	13 variants, default Periodic Ticks
Audio frequency (Hz)	The frequency of the tone. It does not apply to the noise signals and to silence.	from 1, default 440
Audio volume	The volume of the signal as a fraction of full scale.	0–1, default 0.8
Enable overlay	An overlay of text and a clock on top of the picture.	enabled by default
Overlay text	A caption on top of the picture — for example the channel name, to tell several test streams apart on a video wall.	empty by default
Time format (strftime)	The format of the overlaid clock in strftime notation: it is used to measure the end-to-end latency straight from the screen.	empty by default
Total bitrate (kbps)	The total bitrate of the transport stream with NULL-packet padding. Zero — no padding.	from 0, default 0
PNR, PMT PID, Video PID, Audio PID	The program number and the identifiers of the PMT table and of the elementary streams — so as to fit the test stream into the network’s PID plan. The three PIDs must differ from each other.	PNR 1–65535 (default 1); PID 32–8190 (default 32, 33 and 34)