FAB Subtitler LIVE can display live video on the PC screen and also reproduce the audio over the PC speakers. The following live video sources are supported:
- Hauppauge cards for analogue antenna and CVBS video
- DeckLink cards for SD/HD-SDI video
- Video over IP (TS/IP UDP video streams and SRT live streams)
To display live video please use the Display tab and the following functions:
- Editor over video: Displays the video in the active editor window
- Video in a window: Displays the video in a separate window which can also be displayed in full-screen mode on a secondary PC monitor
- Teletext decoder: Displays a window with a teletext decoder
- Video source: Allows changing the video source if the configured video in a window source supports multiple sources (i.e. the channel number for analogue antenna reception or the URL for video over IP)
Hauppauge cards for analogue antenna and CVBS video
Hauppauge cards HVR-1700, HVR-4400 and HVR-5500 are supported, however only for composite video input and analogue antenna input. DVB-T, DVB-C and DVB-S are not supported. Hauppauge cards do not work under Windows Server and therefore Windows 7/10 has to be used.
The following configuration of FAB Subtitler has to be used:
Please note that when using composite video the audio cable has to be connected to the Line In connector of the audio card of the PC.
DeckLink cards for SD/HD-SDI video
DeckLink 4K Extreme and DeckLink Mini Recorder cards have been tested and work correctly with FAB Subtitler LIVE for display of SD/HD-SDI video on the PC monitor. DeckLink cards do not work under Windows Server and therefore Windows 7/10 has to be used.
The following configuration of FAB Subtitler has to be used:
Video over IP (TS/IP UDP video streams)
FAB Subtitler LIVE can receive transport stream over IP (UDP or SRT) and reproduce the video and audio on the PC monitor/speakers. If a teletext PID is present and signalized in the PMT, then teletext will be decoded as well.
To configure FAB Subtitler to use Video over IP please set the following settings:
By clicking on the buttons “Channels” you can define the URLs which are used for every channel that shall be received over IP and displayed. The URL shall be specified as:
udp://239.192.1.120:1234
or
udp://@239.192.1.120:1234
The channel list can also be imported from an XML file in the following format:
<channel-list>
<channel>
<name>ZDF</name>
<url>udp://239.192.1.251:1234</url>
</channel>
<channel>
<name>BR</name>
<url>udp://239.192.1.252:1234</url>
</channel>
<channel>
<name>WDR</name>
<url>udp://239.192.1.253:1234</url>
</channel>
</channel-list>
Because video over IP is generally compressed it is also delayed due to compression. When transmitting LIVE subtitles it is very important that the delay of live video is as low as possible.
The following SD/HD-SDI Encoder was tested by FAB and approved as suitable for live subtitling:
This video encoder produces H.264 encoded video streams which are transmitted over IP. Two channels can be encoded and streamed simultaneously on two separate unicast or multicast IP addresses. The delay between the SDI video and the video that is displayed on the PC screen was measured as less than 200ms for 1080i50 and 720p50 video.
When the video shall be distributed over multicast to multiple PCs a multicast capable network switch will be required. The following multicast capable network switch was tested by FAB and approved as suitable:
URL syntax and parameters
The URL of a channel starts with the protocol: udp://, rtp://, srt:// or http://. Besides the address and the port the URL can contain the following:
| Element | Description |
|---|---|
udp://source_ip@multicast_ip:port |
Source-specific multicast: only packets sent by the given source IP address are received, for example udp://[email protected]:1234. |
url|adapter_ip |
The IP address of the network adapter that shall be used for receiving is appended at the end of the URL, separated with a vertical bar, for example udp://239.192.1.251:1234|192.168.211.8. |
rtp://ip:port1;rtp://ip:port2 |
For udp:// and rtp://: two URLs separated with a semicolon. Video is then received on the first URL and audio on the second URL as raw (not multiplexed) data. |
Optional parameters can be appended to the URL. The first parameter is separated with a question mark, further parameters with an ampersand (&). Parameter names are not case sensitive and parameters that are not known are ignored. A parameter that has an invalid value is reported as an error and the channel is not opened, except bufferms, where the default value is used.
udp://239.192.1.251:1234?pids=256,257,258&bufferms=300
The following parameters can be used with all protocols. They select which streams of a multi-program transport stream are received:
| Parameter | Description |
|---|---|
pids=list |
Comma separated list of PIDs (decimal). Only these PIDs are processed. PID 0 (PAT) is always received. |
pmt=pid |
Receives all streams of the program that has the given PMT PID. |
pcr=pid |
Receives all streams of the program that has the given PCR PID. |
serviceid=id |
Receives all streams of the program that has the given service ID (1 to 65535). |
streams=list |
Comma separated list of PIDs (decimal). Receives all streams of the program that contains these PIDs. |
ttxpid=pid |
Decodes the given PID as teletext, even if it is not signalized as teletext in the PMT. |
vbipid=pid |
Decodes the given PID as VBI data, even if it is not signalized as such in the PMT. |
bufferms=milliseconds |
Delay in milliseconds, from 0 to 5000, that FAB Subtitler adds to video and audio so that they can be reproduced smoothly (default: 200). See below. |
Use only one of pmt, pcr, serviceid and streams in a URL. If a transport stream contains only one program then none of the parameters is needed.
Delay of the live video (bufferms)
FAB Subtitler adds a constant delay to video and audio of the live video before it is reproduced. This delay gives the audio output and the decoding enough time to deliver the data on time, so that the sound does not break up. It is set with bufferms and is 200 ms if the parameter is not used. The live video is thus displayed with the delay that is built into the transport stream by the encoder (this depends on the encoder and is typically between a few hundred milliseconds and 1.5 seconds for HD H.264 video) plus the value of bufferms.
The delay is the same on every PC that receives the same stream with the same bufferms value, no matter at what time FAB Subtitler was started on the PC.
- A lower value reduces the delay of the video. If the sound breaks up or there are gaps in the sound, increase the value, for example to 300 or 500.
- A higher value gives more safety on PCs that are heavily loaded or when the stream arrives with irregular timing, but increases the delay of the video.
udp://239.192.1.251:1234?bufferms=500
SRT live streams
FAB Subtitler LIVE can also receive SRT (Secure Reliable Transport) live streams that carry an MPEG transport stream. SRT recovers lost packets and can be encrypted, which makes it suitable for transmission over the internet or over networks that are not fully reliable. Both SRT connection modes are supported and are selected by the URL that is entered for the channel:
- Caller mode: FAB Subtitler connects to an SRT sender (encoder or server) that is waiting for connections. Specify the IP address or host name and the port of the sender:
srt://192.168.1.50:9000
- Listener mode: FAB Subtitler waits until an SRT sender connects to it. Leave the address empty and specify only the port:
srt://:9000
In listener mode the sender has to be configured as a caller which connects to the IP address of the PC running FAB Subtitler and to this port. The port has to be allowed in the firewall of the PC.
Video, audio and teletext are handled in the same way as for UDP streams. The channels are defined with the button “Channels” as described above.
The following optional parameters for SRT can be appended to the URL in addition to the parameters described above. The first parameter is separated with a question mark, further parameters with an ampersand (&):
| Parameter | Description |
|---|---|
srtmode=caller, listener or rendezvous |
Connection mode. If the parameter is not used, listener mode is used when the address is empty (srt://:9000) and caller mode otherwise. |
srtport=port |
Local port, from 1 to 65535. Used in rendezvous mode. |
srtstreamid=name |
Stream ID of the SRT connection. In listener mode it is checked against the stream ID sent by the caller. |
srtenc=AES-128, AES-192 or AES-256 |
Encryption of the stream. Has to be used together with srtpass. |
srtpass=passphrase |
Encryption passphrase, 10 to 79 characters long. |
srtlatency=milliseconds |
SRT latency from 0 to 10000 ms. A higher latency allows more retransmissions of lost packets on a lossy network, but increases the delay of the video. |
srtrttmultiplier=number |
Multiplier of the round trip time of the connection from 1 to 20, which is used to determine the SRT latency. |
Example of an encrypted stream received in caller mode:
srt://192.168.1.50:9000?srtstreamid=zdf&srtenc=AES-128&srtpass=MySecretPass123
Please note that the SRT latency adds to the delay of the live video. When transmitting LIVE subtitles the latency should be set as low as the quality of the network allows.
SRT connects one sender with one receiver. If the same live video has to be received by several FAB Subtitler LIVE PCs, for example in several home offices or on a local network with UDP multicast, the video forwarder of FAB Subtitler Server can receive the SRT stream and forward it to any number of receivers over SRT or UDP/RTP multicast. It is described here.
DVB-T, DVB-C and DVB-S received from Linux based set top boxes
Linux based set top boxes can be controlled over IP and provide a transport stream over IP which includes teletext. FAB Subtitler can receive the transport stream over http, decode audio, video and teletext and reproduce it.
To configure the Linux set top box correctly please follow these steps:
- We recommend using XTrend ET-8000 receiver because it supports tuners for DVB-S2, DVB-T2 and DVB-C
- We recommend installing the OpenPLI firmware from www.openpli.org on the receiver because it includes the Open Webif Web Interface which provides easy control of the receiver from the web browser. The original firmware will probably also work, however the following screenshots were made with the OpenPLI firmware.
- Connect with a web browser to the receiver, i.e. http://192.168.0.123
- On the web interface enable “Zap before stream”
- Under “Bouquets” search for the channel that you wish to receive and click on “Stream”
- A file stream.m3u will be downloaded. Make sure to store the file on the disk and open it in a text editor. You will find the http URL for the transport stream in this file
To configure FAB Subtitler to use Video over IP please set the following settings:
By clicking on the buttons “Channels” you can define the URLs which are used for every channel that shall be received over IP and displayed. The URL shall be specified as:
http://192.168.0.123:8001/1:0:19:2B66:3F3:1:C00000:0:0:0:
This page was last updated on 2026-10-17