Downsub is a free web application that allows you to extract subtitles from a YouTube, Viki, or VIU video by simply pasting its URL. The resulting file, in SRT, VTT, or TXT format, can then be played in a player like VLC or integrated into an editing project. The principle seems simple, but the synchronization of the downloaded subtitles with the video often poses problems, and the terms of use of these files deserve attention.
Offset of SRT subtitles after download: why the file desynchronizes
The most common scenario after a download via Downsub: the subtitles display one or two seconds ahead of or behind the audio track. This offset has a specific technical origin.
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The subtitles available on YouTube are indexed to the platform’s internal timecode. When the video is streamed, YouTube dynamically adjusts the synchronization based on buffering. The SRT file exported by Downsub, however, relies on fixed timecodes. If the video you are playing locally (in VLC, for example) starts with a slight offset compared to the original stream, the desynchronization becomes audible.
Another factor comes into play when the source video has been re-edited after the subtitles were published. The author may have added an introduction, cut a section, or modified the editing. The SRT file retains the timecodes of the original version, which creates a gradual offset, sometimes increasing throughout the video. A detailed guide explains how to use Downsub on Strat and Geek while considering these scenarios.
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Fixing synchronization in VLC and other video players
VLC includes a manual subtitle correction mechanism that is sufficient in most cases. Two keyboard shortcuts allow you to advance or rewind the subtitle track in increments during playback.
- The H key rewinds the subtitles by 50 milliseconds, while the J key advances them by the same interval. Several successive presses allow for precise adjustment of the offset.
- For a constant offset (the same offset from start to finish), this method resolves the issue in a few seconds without modifying the SRT file.
- For a progressive offset (which worsens throughout the video), manual correction in VLC is not enough. You will then need to edit the timecodes of the SRT file with a dedicated tool like Subtitle Edit or Aegisub.
Aegisub, free software often used in universities for video accessibility, allows you to realign each line of subtitles individually. The procedure involves identifying two synchronization points (one at the beginning, one towards the end of the video) and then applying a proportional realignment across the entire file.
Differences between SRT, VTT, and TXT formats
The SRT format remains the most common for local playback. It contains the start and end timecodes of each line, enabling synchronization. The VTT format, used natively on the web, works similarly but includes additional metadata (positioning, style). The TXT format contains no timecodes: it is limited to plain text, useful for transcription but unusable for synchronized display.
Downsub offers these three formats at the time of download. For any use involving synchronization with the video, SRT or VTT are the only relevant choices.
YouTube auto-generated subtitles: the question of reliability
Downsub does not create subtitles. The tool simply extracts those that exist on the source platform. On YouTube, two types of subtitles coexist: manual subtitles, written by the video author or a contributor, and auto-generated subtitles created by Google’s speech recognition.
The distinction has direct consequences on the quality of the downloaded file. Automatic subtitles have a significant error rate, particularly with proper names, technical terms, and languages other than English. Analyses published in the context of university accessibility guides highlight that these errors sometimes render the text unusable without human proofreading.
Before downloading, check in the YouTube player if the subtitles are labeled “auto-generated.” If so, plan for correction time after extraction. For educational or professional use, prefer videos with manually written subtitles.
Legal framework for downloading subtitles in France
Extracting subtitles via a third-party tool like Downsub raises questions rarely addressed in tutorials. YouTube’s terms of use explicitly prohibit access to the platform’s content through unauthorized automated means. Subtitles, whether manual or automatic, are part of the hosted content.
The European Directive 2019/790 on copyright in the digital single market, transposed into French law in 2021, has strengthened obligations regarding the reuse of user-generated content. Analyses by specialized legal experts published between 2021 and 2023 remind us that extracting subtitles from protected videos can constitute a copyright violation depending on the context of reuse.
However, French law provides an exception to copyright in favor of people with disabilities. Non-profit organizations can create and distribute adapted versions of protected works, including subtitles, without prior authorization from rights holders. This exception particularly covers uses related to accessibility for hearing-impaired individuals.
Legal alternatives for obtaining subtitles
More and more educational and institutional channels (universities, MOOC platforms, public organizations) directly publish their subtitle files for download on their websites, in a “Resources” tab or a dedicated portal. This practice, documented in several video accessibility guides published between 2022 and 2024, makes the use of Downsub unnecessary for these contents while ensuring legal compliance.
Downloading subtitles with Downsub remains a practical tool for quick personal use. The synchronization of the SRT file depends on the stability of the source edit and the type of subtitles extracted. For any use beyond private viewing, verifying the legal framework and the quality of the file is a step that traditional tutorials tend to overlook.