Limecraft can be used to automatically convert audio into high-quality subtitles. Depending on de genre of the content or the type of distribution channel, you may want to modify the styling and timing characteristics of the captions, referred to as 'spotting rules', to optimise for readability.
Using Limecraft, you can pre-configure such spotting rules in advance. These will be taken into account during segmentation of the transcript, thereby minimising the need for post-editing. This article explains how to access the subtitle settings, and how to use the different settings.
TABLE OF CONTENTS
Before you begin
By default, Limecraft uses the BBC style guide. You can modify the timing or styling requirements by editing the existing subtitle preset or create a new preset. Read further to find out how.
For configuring subtitle presets, you need Production Administrator or Admin rights. Navigate to Production Settings > Subtitle Editor to get started.
Select 'Add subtitle preset' to start creating a new preset. Give a descriptive name and an optional description for the subtitle preset. The name should be short as it will be shown in the preset picker in the subtitler when creating a new subtitle.
Configuring how the subtitles are displayed
The first step is to define how your subtitles are displayed in the player.
Preview area
With the region configuration you can define where the subtitles appear on the video frame. This section lists the available regions you can choose from in the Subtitle Editor, Top region and Bottom region. You can change their position and size here.
The black rectangle below is the preview area which represents your video frame.
There are three buttons below the preview area which let you change the subtitle preview to better correspond to your intended material. You can change the text in the preview area, pick an image to use as a preview, and change the aspect ratio from the default 16:9 to one of your choosing.
Note: changes made with these buttons do not result in changes in the production preset settings. They are only used to change the preview, and the default preview is restored after refresh.
Region Configuration
You can drag and resize the regions (cyan rectangles) to your desired settings.
Another option to set the position and the size of the regions is by configuring the values below. The values are given in percentages relative to the video frame size. Changing these values will immediately update the preview area.
With X and Y you can change the position of the top left corner of the region.
- X=0% will put the lift side of the region at the left side of the video frame.
- X=100% will put the left side of the region at the right side of the video frame (outside the visible area)
- Y=0% will put the top side of the region at the top side of the video frame.
- Y=100% will put the top side of the region at the bottom side of the video frame (outside the visible area)
Layout
Besides the overall position of the captions, you can specify the details of the layout of the captions and the background as follows.
The Cell resolution defines a cell grid over the video frame. In the example, the grid is 32 cells horizontally by 15 cells vertically. This is also shown in the preview area.
The Line-Padding is the extension of the background color on the left and right of each subtitle line. Its width is defined relative to the width of a single cell (in the example, 50% or half a cell’s width is used).
The Line-Height sets the inter-baseline separation between line areas. It is expressed relative to the Font-Size. In the example, the Line-Height is 120% of the Font-Size.
The Font-Size is defined relative to the height of a single cell. In the example, 100% is used.
Fill line gap is used to control whether the background color fills the entire line height, or only the height of the font size (in which case gaps might occur).
Example with ‘Fill line gap’ unchecked (and a line height of 130% the font size)
Example with ‘Fill line gap’ checked (and a line height of 130% the font size)
Styling
Background Color defines the background color of the subtitles.
Background Opacity sets the transparency of the color (0% opacity = fully transparent, 100% opacity = not transparent at all).
Align defines if the text aligns to the left, center or right.
Font allows you to select the font if custom fonts have been configured.
NOTE: The Limecraft default font is Arial. With some OS Helvetica or Sans Serif might be used. If you wish to use other fonts, please contact [email protected].
Subtitling colours
In this section you can determine the colours that are available in the Subtitle Editor color menu.
This is how it is shown in the Subtitle Editor.
Subtitling 'Spotting Rules'
Subtitling 'spotting rules' are crucial for ensuring that subtitles are clear, readable, and synchronised with the audio and visual content. Spotting rules may vary on the type of content, language, and distribution channel. If you are not familiar with spotting rules, please refer to this article on the knowledge base.
In this section, you will learn how to the properly set spotting rules or timing of the subtitles.
Character limits
Character limits defines the maximum number of characters that a single line of a subtitle can contain. The automatic subtitle spotting algorithm will undertake to respect the soft limit ("Max characters"), and will allow up to the hard limit if necessary.
?The number of characters may be different to optimise for readability, taking into account the type of content, the reading speed, and the specifics a particular distribution channel:
- When subtitling television content, a restriction of 38 or 40 characters on a line may be applied by the broadcaster;
- When producing subtitles for most streaming applications like Netflix, usually a restriction of 42 characters on a line applies;
- When creating square or vertical video for social media, best practice is to use a maximum of 27 characters on a line.
Lines limits
You may want to indicate the maximum number of lines allowed to create subtitles. The AI subtitling will undertake to use the limit defined by "Max lines", and it will allow to the "hard lines limit" if necessary.
?The number of lines is indirectly related to the type of distribution:
- When creating subtitles for conventional television distribution or streaming services, the number of lines ('Hard lines limit') is typically restricted to 2;
- When creating subtitles for square or vertical video, given the number of characters per line is usually restricted to 27 (in stead of 38-42), best practice is to allow up to 3 lines of subtitles.
Sentence splitting
When splitting a sentence, you can add a suffix to the end of the first part and a prefix to the start of the second part.
? While not mandatory, it may be helpful to use "..." as a pre-and suffix to indicate that sentences are split over different subtitles.
Reading speed
The reading speed is expressed by the number of words per minute, and it is calculated by dividing the number of words in a subtitle by the lenght in minutes it remains on screen. Best practice is to use an upper limit of +/- 180 words per minute, to avoid the subtitles disappearing too fast.
Subtitle appearance timing
To avoid a stroboscopic effect, subtitles should be aligned with the rhythm of the edit. More specifically, if the in or out point of a subtitle (based on clean cut segmentation of the transcript) would be close to a shot cut, it is best practice to modify the timing of the subtitle to make sure subtitles change at the same time as the shots in the video. Using Limecraft, you can configure the sensitivity of the synchronisation, by configuring the maximum time difference between subtitle and shot changes (measured in seconds). The AI subtitling algorithm will take this into account when converting the transcript into subtitles, so as to minimise of avoid post-editing of the automatically generated subtitles.
Text to digits
Limecraft AI subtitling can automatically substitute textual numbers ("twenty three") with digits (23). This rule is evaluated prior to the "Digits to Text" rule.
Digits to Text
Limecraft can replace digits with words ("23" to "twenty three"). Usually you only want to do this for smaller numbers, so you can set up a range of numbers which you want to replace with words.
The last option allows you to exclude certain contexts from replacing. At the moment only "Measurements" can be excluded (digits followed by units).
It is important to note that the "Text to Digits" rule is evaluated first, and then the "Digits to Text rule. So text converted to digits by the first can be converted to text again by this rule.
Subtitle Fade out, minimum gap between subtitles, and snap to next timing
The "Fade out" define how long the subtitle lingers on the screen after the last spoken word was heard.
The "Minimal gap" makes it possible to force a timing gap between the end of a subtitle and the beginning of the next subtitle.
The"Snap to next threshold" will postpone the disappearance time of a subtitle to the start of the next subtitle (minus the "minimal gap").