Filters
Filters are transformation functions that operate on caption data between the decode and encode steps. Every filter receives a Closed Caption Project (CCPRJ) object, applies its transformation, and returns an updated CCPRJ. Because filters work at the CCPRJ level they are format-agnostic — the same filter configuration works the same way regardless of whether you are converting SCC to SRT or TTML to WebVTT.
Filters are configured individually and applied in the order they appear in your job configuration. In the web application you can add as many filters as needed, reorder them by dragging, and remove individual filters using the remove button on each row.
Timing & Sync
The Timing & Sync filter is the primary tool for all timecode and frame rate operations. It controls the frame rate used to interpret source timecodes, the frame rate written to the target file, and any offset or adjustment applied to event timecodes during processing.
The filter exposes a Default Frame Rate that is used when the source format does not carry frame rate metadata and Closed Caption Converter cannot automatically detect it. The Source Frame Rate can be set explicitly or left on auto to let the engine read frame rate from the file. The Target Frame Rate determines the frame rate written into the output file. If source and target frame rates differ, all timecodes are mathematically converted. Drop-frame flags can be set independently for source and target.
In addition to frame rate conversion, the Timing & Sync filter supports a Timecode Offset, which shifts all event in and out times by a fixed SMPTE timecode value — useful for resyncing content to a new programme start. An Incode value can also be set to establish a new programme start time that all events are normalised against. Setting Incode to auto uses the detected first event as the programme start.
Stretch & Sync mode is available for cases where you have a reference point (such as a known dialogue line at a specific time) and need to proportionally scale all timecodes to match. This is useful when a file was created at one frame rate but the timecode numbers were not converted.
Segmentation & Conform
The Segmentation & Conform filter is used to extract one or more segments from source caption files and combine them into a single output file. It is essential in NLE-based workflows where a programme is assembled from multiple reels or edited segments, and the caption file must be conformed to match the final edit.
Each segment defines a region of the source file to extract using a start and end timecode. Timecodes can be expressed as SMPTE timecode (HH:MM:SS:FF), millisecond timecode (HH:MM:SS.mmm), seconds (0.000), or frame count. Multiple source files with different frame rates can be included in a single segmentation job, and each segment can specify its own source file reference.
When segments are assembled, you can optionally insert blank space between them using the Frame Gap setting. This is commonly used to place filler between segments in multi-reel deliveries that require silence between acts.
Auto Format
The Auto Format filter automatically re-wraps caption event text to conform to maximum line and character constraints. It breaks long lines at natural word boundaries and attempts to produce visually balanced subtitle lines. This is most useful after translation workflows (where translated text may be significantly longer than the original) or when converting from a format that has no line-length restrictions into one that does.
Maximum Lines and Maximum Characters define the upper bounds that every caption event must conform to. The engine will split events that exceed these limits. Minimum Event Duration sets the shortest allowed event in seconds — events shorter than this after splitting will not be split further.
Selective Format mode leaves events that are already within the configured limits unchanged, only reformatting those that exceed them. This is the recommended setting when you want to preserve existing formatting decisions in a file and only correct violations.
Allow Orphan Words controls whether the formatter may produce a single-word line when text balancing requires it. When disabled, single-word lines (orphans) are merged back with the preceding line even if doing so causes that line to exceed the maximum character limit.
Automatic Reading Speed
The Automatic Reading Speed filter adjusts the duration of caption events to ensure they meet reading speed targets. It is designed to make captions readable at a natural pace for viewers, which is especially important after format conversion or when caption timing is generated from transcription.
The filter can work in two modes: Characters Per Second (CPS) and Words Per Minute (WPM). You set a target CPS or WPM value, and the engine calculates the minimum duration each caption event must be on screen to be readable at that speed. If an event is shorter than the required minimum, its out-time is extended. The filter is aware of gaps between events and will not push an event's out-time past the in-time of the next event.
Search & Replace
The Search & Replace filter finds and replaces text strings within caption events. It supports both literal string matching and full regular expression patterns, making it suitable for everything from simple terminology corrections to complex structural transformations of caption text.
Each rule specifies a Find pattern and a Replace value. Rules are evaluated in order. Regular expression mode supports standard ECMAScript regex syntax including capture groups (referenced as $1, $2, etc. in the replacement string), character classes, and lookahead assertions.
Multiple rules can be added to a single filter, allowing you to apply a complete set of corrections in a single pass. This is commonly used to normalise terminology, remove unwanted formatting codes that survive format conversion, or apply company-specific spelling and style policies to caption text.
Event Gap
The Event Gap filter inserts a blank frame gap between adjacent caption events. Many streaming platforms (including Netflix) require a minimum number of blank frames between events to prevent captions from appearing to "flash" when one event immediately follows another. The Event Gap filter automates this correction across an entire file.
The Minimum Gap setting defines the number of blank frames that must exist between the out-time of one event and the in-time of the next. When the gap between two events is smaller than this value, the out-time of the earlier event is pulled back to create the required gap. The filter accepts Minimum and Maximum tolerance values — events with a gap already within this range are left unchanged.
The filter is Shot Change Aware: if shot change data is embedded in the source file, the filter will not pull an event's out-time across a shot change boundary. Fix Event Overlaps can be enabled in conjunction with Event Gap to first correct any events that already start before the previous one ends, before applying gap insertion.
Auto Correct Timing
The Auto Correct Timing filter automatically corrects common timecode issues in caption files without requiring manual frame rate or offset configuration. It is most useful for files that have gone through multiple format conversions or editorial passes where small timing errors have accumulated.
The filter detects and optionally corrects events where the out-time equals the in-time (zero-duration events), events where the out-time is before the in-time (inverted events), and events that overlap with adjacent events. It can also reset the programme start timecode to 00:00:00:00 by shifting all events relative to the first detected event, which is useful when preparing content for delivery specifications that require captions to begin at zero.
Caption Style
The Caption Style filter provides control over text styling attributes applied to caption events: font, size, color, italics, bold, underline, and positional properties. It is most commonly used to normalise styling across a file (for example, stripping all inline formatting and applying a uniform style) or to apply the mandatory styling requirements of a specific delivery specification.
The filter can operate in Override mode, which replaces all existing style information with the configured values, or in Apply If Missing mode, which only sets style properties on events that have no existing styling. Individual style attributes can be enabled or disabled independently, allowing you to normalise only specific properties while leaving others untouched.
Reposition
The Reposition filter adjusts the screen position of caption events. It supports shifting events to a new row or screen region, applying safe-area offsets, and normalising position data that may have been carried through from a source format with a different coordinate system.
Position rules can be applied globally across all events or selectively based on the current position of each event. This is useful when converting between formats with incompatible positioning schemes — for example, converting a subtitle file that uses absolute pixel coordinates into a broadcast caption format that uses row numbers.
Remove Forced Subtitles
The Remove Forced Subtitles filter strips forced subtitle events from a caption file. Forced subtitles are events that are marked as appearing even when the viewer has subtitles disabled — they are typically used for translated dialogue, signs, or on-screen text in foreign languages. Some delivery workflows require a version of the subtitle file that contains only the forced events, and others require the full subtitle track with forced events removed.
The filter can be configured to either remove all forced events or retain only forced events, producing the correct output for either delivery scenario without needing to manually edit the source file.
Automatic QC
The Automatic QC filter analyses caption events against a configurable style guide and flags events that violate the defined rules. Unlike other filters that transform caption data, QC does not change any events — it populates each event with issue markers that identify the specific violations detected. These issue markers are visible in the job output and can be used to generate QC reports or trigger review workflows.
The filter has two independent test plans that can be enabled together or separately:
Content QC checks the text of each caption event against a set of configurable thresholds. Available checks include minimum and maximum character count per event, minimum and maximum line count, minimum and maximum word count, minimum and maximum event duration (in frames), minimum and maximum frame gap between events, minimum and maximum characters per second (CPS), minimum and maximum words per minute (WPM), detection of overlapping events, illegal CEA-608 characters, and illegal Netflix characters.
Technical QC checks the structural and metadata properties of the file rather than its text content. It validates frame rate metadata, timecode format consistency, and format-specific technical requirements.
The advantage of running QC as a filter rather than a standalone step is that it can be combined with corrective filters in a single job — for example, first applying Auto Format and Event Gap to correct known issues, then running QC to verify the result meets delivery specifications.
HD Caption Options (CEA-708)
The HD Caption Options filter configures CEA-708 digital caption service properties for output to formats that carry 708 data, primarily MCC and embedded broadcast streams. CEA-708 supports multiple caption services with independent style, language, and positioning settings.
The filter exposes configuration for the 708 Service Number (the caption channel), Language, window styling attributes including font style and size, and the 708 caption type. These settings are written into the output file's 708 service metadata and interpreted by caption decoders in hardware and software players.
SD Caption Options (CEA-608)
The SD Caption Options filter configures CEA-608 analogue caption channel properties for output to formats that carry 608 data, including SCC and MCC. CEA-608 supports two channels (CC1/CC2 and CC3/CC4) and three caption modes.
The filter allows you to specify the Channel (CC1, CC2, CC3, or CC4) and the Caption Mode (pop-on, paint-on, or roll-up). Channel assignment is important in multi-language deliveries where CC1 carries the primary language and CC3 carries a secondary language. Mode selection affects how captions are rendered on-screen: pop-on delivers captions as a complete block that appears simultaneously, paint-on paints characters one at a time from left to right, and roll-up scrolls new lines up from the bottom of the screen.
Window
The Window filter defines the safe-area window within which caption text must be positioned. It sets the width and height of the caption area in columns and rows, which the encoder uses to constrain event placement relative to the displayable area of the screen.
For broadcast formats, the standard window is 32 columns × 15 rows (the CEA-608/708 grid). For subtitle formats, the window is used to calculate the percentage-based position values written into TTML or WebVTT. Adjusting the window is most commonly required when converting between formats with different safe-area definitions or when a delivery specification requires a specific caption area inset from the screen edges.
File Encoding
The File Encoding filter sets the character encoding used when writing text-based output files. Most modern subtitle formats use UTF-8, but some legacy broadcast systems and older players require files in Latin-1 (ISO-8859-1), Windows-1252, or other encodings.
Selecting the correct file encoding is important for files that contain accented characters, special symbols, or non-Latin scripts. Writing a UTF-8 file when a legacy system expects Latin-1 will produce corrupted characters in the output. The filter also controls the line ending style (CRLF or LF), which may be significant for systems that are sensitive to line ending format.
Embed Options
The Embed Options filter configures how caption data is embedded into container file formats that support multiplexed caption tracks. This is used when outputting a caption-in-media-container format where captions are stored alongside video metadata rather than as a separate file.
The filter controls whether captions are written as a sidecar track or muxed into the container, and configures container-specific metadata such as track language and service identifiers.
V-Chip Information
The V-Chip Information filter writes TV parental guideline rating data into the output caption file. V-Chip ratings are carried in the CEA-608 XDS data channel and are read by television sets to enable parental controls. They are required in North American broadcast deliveries.
The filter allows you to set the Content Rating (TV-Y, TV-Y7, TV-G, TV-PG, TV-14, TV-MA) and any applicable Content Advisories (Violence, Sexual Content, Adult Language, Sexually Suggestive Dialogue). These values are encoded into the XDS stream in the output file according to the CEA-608 specification.
Program Information
The Program Information filter writes programme metadata into the output caption file. For SCC files, this is stored in the XDS (Extended Data Service) stream. For other formats it populates the relevant metadata fields supported by that format.
Available fields include programme name, network name, content type (series or movie), start time, duration, and audio format. This data is used by broadcast systems for automated logging, scheduling integration, and programme identification. It is required for some broadcast delivery specifications that mandate XDS programme identification data in SCC files.