# Subtitle Platform Spec Checker Validate subtitles against delivery specs: Netflix Timed Text (20/17 CPS reading speed, 42 characters per line, two lines, 5/6-second minimum and 7-second maximum durations, 2-frame gaps), BBC television guidelines (37 characters per line, 160-180 wpm, 1.5-second pause gaps) and YouTube caption rules (plain UTF-8, markup not recognized) — with a per-cue findings report. > Canonical page: https://elysiatools.com/en/tools/subtitle-platform-spec-checker - **Category:** Media - **Keywords:** netflix subtitles, timed text style guide, cps, characters per second, reading speed, bbc subtitle guidelines, youtube captions, srt validator, vtt validator, ttml check, 42 characters, 37 characters, subtitle spec, caption quality, line length, subtitle duration ## Overview Platform subtitle delivery lives or dies on reading speed and line discipline. The Netflix Timed Text Style Guide allows up to 20 characters per second on adult programs and 17 CPS on children’s programs, 42 characters per line, a maximum of two lines per subtitle event, a minimum duration of 5/6 of a second (20 frames at 24 fps) and a maximum of 7 seconds per event, and requires at least a 2-frame gap between events at any frame rate (their timing guide allows chaining gaps up to exactly 2 frames). The BBC Subtitle Guidelines keep the teletext heritage of 37 fixed-width characters per line and two lines, recommend a reading speed of 160-180 words per minute (about 0.3 seconds of on-screen time per word as a floor) and ask for gaps of a second and a half where speech pauses. YouTube accepts SRT and WebVTT as plain UTF-8 text: style markup like <i>/<b>/<u>/<font> is simply not recognized in SRT and positioning/styling in VTT is limited, so markup is reported as a warning rather than silently lost. This checker parses SRT, WebVTT, SBV and TTML with the shared subtitle engine, measures every cue (characters per line including spaces, lines per cue, CPS = characters ÷ duration, words per minute, durations and inter-cue gaps converted to frames at the frame rate you declare) and grades each violation as fail (hard spec limit) or warn (guideline recommendation), with overlap, negative-duration, empty-cue and non-monotonic structural checks always on. The report card summarises the tightest offenders and lists every finding by cue number, so a file can be fixed against the exact rule before delivery. ## Inputs - **Subtitle file** (file) - **Platform profile** (select) - **Frame rate (fps)** (number): 24 ## When to use - Preparing caption or subtitle deliverables for Netflix, BBC broadcast, or YouTube distribution. - Checking files for reading speed violations (CPS or WPM) and line character limits before QC sign-off. - Auditing timed text for structural issues like overlapping timestamps, sub-frame gaps, or unsupported HTML markup. ## How it works - Upload your subtitle file formatted as SRT, WebVTT, SBV, or TTML. - Select the target platform profile (Netflix Adult, Netflix Kids, BBC TV, or YouTube) and specify the project frame rate. - The tool parses each cue, calculating reading speed, characters per line, event durations, and frame gaps between consecutive cues. - Review an HTML report detailing conformant metrics, overall pass/fail status, and a per-cue log of warnings and hard errors. ## Use cases - Localization agencies verifying vendor subtitle files against the Netflix Timed Text Style Guide. - Broadcasters ensuring captions comply with BBC line-length limits and pause gap standards. - Online video creators cleaning up unsupported italic, bold, or font tags from YouTube SRT files. ## Frequently asked questions ### What file formats does the checker support? The checker supports SRT, WebVTT (.vtt), SBV, and TTML (.ttml or .xml) subtitle files up to 20 MB. ### How are characters per second (CPS) calculated? CPS is calculated by dividing total characters, including spaces, by the cue's duration in seconds. ### Why does the frame rate (fps) matter during verification? The frame rate converts inter-cue gap timings into frame counts to verify platform requirements like Netflix's 2-frame minimum gap. ### What is the difference between a fail and a warn result? Fail indicates a breach of hard platform constraints, while warn flags guideline recommendations or unparsed formatting tags. ### Does the tool check for overlapping or empty cues? 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