Filmhub is one of the most important distribution platforms for independent filmmakers, connecting films with streaming services, airlines, educational platforms, and broadcasters worldwide. One of the most common reasons for a Filmhub submission to be delayed or rejected is caption file issues — either the wrong format, technical violations of their caption requirements, or missing captions entirely.
This guide covers everything you need to know to prepare a caption file that passes Filmhub's QC requirements first time.
Filmhub is a film distribution platform that aggregates independent films and distributes them to over 100 streaming services, VOD platforms, airlines, and educational services globally. Unlike traditional distributors, Filmhub operates on a revenue-share model with no upfront fees, making it accessible to independent filmmakers at all levels.
Captions are not optional on Filmhub — they are required for all content. This is partly a practical requirement (many of Filmhub's downstream platforms require captions as a condition of carriage) and partly an accessibility requirement. A film submitted without captions, or with captions that fail technical QC, cannot be distributed until the issue is resolved.
| Requirement | Filmhub Limit |
|---|---|
| File format | SRT (.srt) |
| Maximum characters per line | 43 |
| Maximum lines per caption | 2 |
| Maximum reading speed | 25 characters per second (CPS) |
| Minimum caption duration | 600 milliseconds (0.6 seconds) |
| Maximum caption duration | 8,000 milliseconds (8 seconds) |
| Minimum gap between events | 66 milliseconds (0.066 seconds) |
| Audio synchronisation | Within 0.5 seconds of corresponding audio |
| Encoding | UTF-8 |
Filmhub allows a maximum of 43 characters per line — slightly more permissive than Netflix's 42 character limit but still a hard cap. Every individual line within a caption block must stay at or below 43 characters. This includes spaces, punctuation, and any speaker identification labels. SRT formatting tags such as <i> and </i> are not counted toward the character limit as they are not rendered as visible characters.
When creating or editing captions, aim for natural line breaks at clause boundaries rather than filling every line to the maximum. A caption with two lines of 35–38 characters each is easier to read than one with both lines pushed to 43 characters.
Filmhub's 25 CPS limit is significantly more permissive than Netflix's 17 CPS — it allows captions to move substantially faster across the screen. However, it is still an enforced limit and captions that exceed it will fail QC. The 25 CPS limit is calculated the same way as any CPS measurement: total characters in the caption block divided by the display duration in seconds.
Filmhub's more permissive CPS limit reflects the platform's independent film context, where captions are sometimes closer to subtitle translations of foreign dialogue than traditional closed captions for English-language content. However, it is worth noting that even if a caption passes Filmhub's 25 CPS QC, downstream platforms that Filmhub distributes to may have lower CPS requirements. If your film is likely to be picked up by Netflix through Filmhub's distribution network, targeting Netflix's 17 CPS limit from the start is the safer approach.
Each caption event must be on screen for a minimum of 600 milliseconds (0.6 seconds) and a maximum of 8,000 milliseconds (8 seconds). Captions shorter than 600ms are too brief for viewers to read regardless of their length and are typically the result of a timecode error. Captions longer than 8 seconds are usually an indicator that a single caption block is trying to cover too much dialogue and should be split into multiple events.
A caption that sits on screen for 8 seconds covering a long speech is almost always better served by two or three shorter caption events that each cover a natural section of the dialogue. This also helps manage the CPS rate, as splitting a long caption reduces the character count per event.
There must be a minimum gap of 66 milliseconds between the end of one caption event and the start of the next. This gap is slightly smaller than Netflix's 2-frame minimum but is still strictly enforced. Back-to-back captions with no gap, or with a gap smaller than 66ms, will fail Filmhub's QC.
When editing captions to create the required gap, a practical target is 100–150 milliseconds. This comfortably exceeds the 66ms minimum, is barely noticeable to viewers, and provides a buffer against any rounding differences in timecode precision between different software tools.
Filmhub requires captions to be synchronised within 0.5 seconds of the corresponding audio. This means each caption should appear no more than 0.5 seconds before or after the dialogue it represents begins. This requirement cannot be checked by Caption QC as it requires comparison against the audio track, but it is one of the most common reasons for manual QC rejection on Filmhub.
If your captions were generated by an automated transcription service, they are usually well synchronised to the audio. If they were manually created or imported from a script, synchronisation errors are more likely. The best way to verify synchronisation is to watch the film with the captions on and check that captions appear at the right moment throughout.
Filmhub requires captions in SRT format (.srt file extension) encoded as UTF-8. UTF-8 is the most common text encoding and is the default in most modern subtitle editing software. If you are unsure about the encoding of your SRT file, most text editors can display and convert the encoding — look for an "encoding" option in the save or export dialog.
Filmhub does not currently accept WebVTT (.vtt), TTML, or other caption formats for primary caption delivery, though requirements may evolve as the platform develops.
Before submitting your caption file to Filmhub, work through this checklist:
Caption QC includes a built-in Filmhub preset that automatically sets the correct thresholds for characters per line (43), lines per caption (2), reading speed (25 CPS), minimum duration (600ms), maximum duration (8 seconds), and minimum gap (66ms). Running your SRT file through Caption QC with the Filmhub preset selected will check all of these requirements automatically and flag any violations before you submit to Filmhub.
The one requirement Caption QC cannot check is audio synchronisation, as this requires comparison with the actual video and audio. All other Filmhub technical caption requirements are fully covered by the tool.
Check your SRT file against Filmhub's requirements before submission — free, in your browser.
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