There are several settings which are important for optimum quality of subtitles produced by live transcription in FAB Subtitler.
Recognition delay
This delay can be set for every transcription engine.
This setting defines how long FAB Subtitler will wait for a reliable live transcription result text before using it to create a subtitle.
- The longer the delay the better the recognition quality will be.
- You can reduce this delay to reduce the delay as much as possible.
- In configurations where the video is delayed, a setting of 5500ms is a good choice so that also subtitles can be delayed.
Different transcription engines provide results in a different manner:
- Microsoft generally works well already with 3000ms recognition delay.
- FAB Subtitler Server may require at least 4000ms to provide good results, 5500ms will provide very good results.
Compensating video encoding delay for live transcription
FAB Subtitler can compensate the delay of live transcription by compensating the delay of the video through the SDI/MPEG encoding/transmission chain.
To make use of this feature it is necessary to know the delay of the SDI/MPEG encoding/transmission chain and configure it in FAB Subtitler.
The configuration of the delay is done in Options / System / Active outputs:
Define the delay of the video for every output separately. In above example the configured delay is 5 seconds. This means that subtitles will be transmitted with 5 seconds delay so that they will be displayed at the correct time on the reception device because the video is also delayed 5 seconds.
In case of live transcription FAB Subtitler will consider the delay of live transcription:
- when transcribed subtitle already has 4 seconds delay because of transcription delay then it will not be transmitted with 5 seconds delay but with only 1 second delay. In this case the subtitle will appear on the reception device without delay at the correct time.
- when transcribed subtitle already has 7 seconds delay because of transcription delay then it will not be transmitted with 5 seconds delay but without delay. In this case the subtitle will appear on the reception device with 2 seconds delay.
Conclusion: If the delay of the video is long enough (for example 10 seconds) or the SDI/MPEG encoding equipment can be configured to delay the video for 10 seconds then live transcribed subtitles can appear without delay.
The following picture tries to explain delays in the transmission chain for DVB and teletext subtitles in TS:
Configuring live text formatting
FAB Subtitler applies certain rules to create subtitles from live text received from live transcription. The settings which influence this conversion are available in Options / Special / Live text formatting:
-
Use the following word substitution file: A text file can be provided which can replace words that were recognized incorrectly by correctly spelled words. You can find a sample of such file here
-
Send mode:
- By blocks: A subtitle will be transmitted as a complete subtitle and text will never be added to the subtitle that is already displayed.
- Word by word: New words will be added to the subtitle when they are received from transcription.
- Word by word with scroll: Same as “Word by word” but lines will be scrolled.
-
Default text justification: defines whether the subtitle should be left or right justified or centered
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Default vertical position: defines whether the subtitle should be display on the bottom or on the top of the screen
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Number of subtitle lines: Defines how many lines of text shall be used in the subtitle.
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Reading speed (characters/sec): will be used to calculate the display time of a subtitle.
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Maximum reading speed when text is lagging (characters/sec): will be used to calculate the display time of a subtitle when more than one subtitle remains untransmitted.
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Send incomplete subtitles after (ms): defines how long FAB Subtitler will wait to receive enough text to fill a complete subtitle before sending the subtitle with the text that as received until that moment.
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Delay deletion of last subtitle, clear after (ms): when a subtitle is displayed and no more text is received the deletion of this subtitle will be delayed by the specified value
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Minimum subtitle duration (ms): a subtitle will never be displayed for less time than specified here
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Apply the following user defined style: A fixed user defined style can be applied to live transcribed subtitles to make sure that such subtitles appear always in the same color or at the same position (for example at the top of the screen). User defined styles are explained here.
The following settings will only work with some transcription services. This depends whether the transcription service returns the necessary data:
- Insert new line and the following setting on speaker change: Defines the character(s) which will be inserted into the subtitle so that the viewers are informed about the speaker change.
- Add the same characters also into the first subtitle line: When active, the same characters are inserted also into the preceding subtitle line.
- Rotate the following colors on speaker change: Defines which colors shall be used on every speaker change. To use white and yellow text specify: 1,2
- Detect music after number of seconds and insert the following text: Defines how many seconds of music must be present and detected so that the entered text will be transmitted in the subtitle.
Live text formatting for MS Azure
The following settings are recommended when using the MS Azure cloud service:
Controlling vertical position of live transcribed subtitles
FAB Subtitler BCAST/XCD can transmit live transcribed subtitles on a non-standard (not bottom-justifed) position. This can be controlled by
- configuration setting
- FAB Automation Protocol command over TCP or REST API
In the configuration this can be defined here:
To define the vertical position with FAB Automation Protocol commands over TCP or REST API use these commands:
COMMAND=STARTFILE;FILENAME=ID001;DATA=TC:10:00:00:00,SOURCE:TRANSCRIPTION,VOFFSET:TOP
or
COMMAND=SETVOFFSET;DATA=TOP
Example using curl.exe:
curl.exe http://ip:port/automationsystem/STARTFILE;FILENAME=ID001;DATA=TC:10:00:00:00,SOURCE:TRANSCRIPTION,VOFFSET:TOP
This page was last updated on 2025-02-04