SubC – Subtitle Converter — Convert SRT, VTT, ASS with Ease

SubC – Subtitle Converter: Batch Convert & Sync Subtitles QuicklySubC is a lightweight yet powerful subtitle conversion tool designed for anyone who works with video captions — from professional editors and subtitlers to hobbyists and educators. Its core promise is simple: convert multiple subtitle files at once and keep timings accurate across formats. This article explains what SubC does, why it matters, how it works, and practical workflows to help you get consistent, compatible subtitles fast.

Why subtitle conversion matters

Video content lives across platforms and devices, and each target environment often prefers or requires a specific subtitle format. Common formats include:

• SRT (SubRip) — widely supported, simple, timecode-based plain text.
• VTT (WebVTT) — used on the web, supports extra styling and cues.
• ASS/SSA (Advanced SubStation Alpha) — rich styling, often used for anime fansubbing and broadcast.
• SUB/IDX, SBV, and others — legacy or platform-specific formats.

Converting between formats is more than just renaming files. Differences in timestamp resolution, cue numbering, styling syntax, and encoding can break readability or timing. Batch conversion and accurate syncing save hours of manual fixes, particularly for series, lecture recordings, or localized releases.

Key features of SubC

• Batch conversion: process hundreds of files in one job.
• Multi-format support: SRT, VTT, ASS/SSA, SBV, and others.
• Timecode preservation and resampling: maintain sync when frame rates differ.
• Offset and scaling tools: shift or stretch timings to match video edits.
• Encoding detection and conversion: automatic handling of UTF-8, UTF-16, Windows-1251, etc.
• Styling translation: map simple styles between formats (bold/italic/italics, colors, positioning).
• Error detection & repair: detects overlapping cues, malformed timestamps, and common syntax errors.
• Command-line and GUI modes: integrate into scripts or use a point-and-click interface.
• Batch preview and dry-run: inspect changes before writing files.

SubC’s strengths are speed, reliability, and practical tools for real-world subtitle workflows.

How SubC handles timing and sync

Accurate timing is the hardest part of subtitle conversion, particularly when:

• Source subtitles use a different frame rate (e.g., 23.976 fps vs 25 fps).
• Video has been edited (segments cut or stretched).
• Subtitles use different timecode formats or rounding rules.

SubC offers multiple sync strategies:

1. Direct copy — for formats with compatible timestamps (e.g., SRT → VTT).
2. Frame-rate resampling — converts timestamps by applying a ratio based on source and target frame rates: t_target = t_source * (fps_source / fps_target)
3. Offset adjustment — apply a uniform shift (positive or negative milliseconds) to all cues.
4. Time scaling — stretch or compress cue timings linearly to match edited video duration.
5. Anchor-based sync — use matching cue text or manually-specified anchor points to compute non-linear time warps for sections with variable drift.

SubC reports potential issues (overlaps, very short cues) and can optionally fix or flag them for user review.

Example workflows

Below are common scenarios and step-by-step approaches using SubC.

Workflow: Batch convert a TV series from ASS to SRT

1. Collect all episode ASS files into one folder.
2. Open SubC GUI or run the command: subc –input ./ass-files –output ./srt-files –from ass –to srt –batch
3. Choose styling mapping: strip advanced ASS tags, keep italics.
4. Run a dry-run preview, then execute conversion.
5. Spot-check a few episodes in a player supporting SRT.

Workflow: Convert SRT to VTT and adjust for a 25 fps master

1. subc –in episode.srt –out episode.vtt –to vtt –fps-src 23.976 –fps-tgt 25
2. Review cue spacing in the preview to ensure no overlap after resampling.

Workflow: Sync subtitles to edited video using anchors

1. Identify 3–5 spoken lines present in both subtitles and video (or use embedded reference timecodes).
2. Use subc –anchors anchor-file.json to apply non-linear warp.
3. Verify continuity across cuts.

Command-line examples

All multi-line code must be fenced; here are representative commands:

# Batch convert ASS to SRT in a folder subc --input ./ass_folder --output ./srt_folder --from ass --to srt --batch # Convert with frame-rate resampling subc --in ep01.srt --out ep01_converted.vtt --to vtt --fps-src 23.976 --fps-tgt 25 # Apply global offset of +1.2 seconds subc --in captions.srt --out captions_shifted.srt --offset 1200 # Dry-run batch preview (no files written) subc --input ./raw_subs --output ./preview --batch --dry-run 

Tips for consistent results

• Always keep a backup of original subtitle files before batch operations.
• Use dry-run to preview changes and spot destructive edits.
• Normalize encodings to UTF-8 when possible to avoid character corruption.
• When converting from rich formats (ASS) to simple ones (SRT), decide how to handle styling — strip, convert, or embed markers (e.g., ).
• If audio/video editing changed duration, prefer anchor-based or time-scaling sync rather than simple offsets.
• Use checksums or filename conventions to keep versions organized during batch jobs.

# daily job to convert all new ASS files to SRT find /media/submissions -name '*.ass' -mtime -1 -print0 | xargs -0 -I {} subc --in {} --out /media/converted/$(basename {} .ass).srt --from ass --to srt