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Preparing, uploading and editing video captions

Updated March 26, 2021

Video captioning is a significant part of Clowdr’s commitment to accessibility:

  • Clowdr auto-generates subtitles for all uploaded videos.
  • Clowdr has a built-in editor that gives authors the opportunity to correct any errors in the captions - as can happen with technical terms and acronyms!
  • All captions are included when exporting videos from Clowdr to YouTube.
  • All recordings of livestreamed events are run through our subtitle auto-generator before they are published. The captioned recordings of livestreamed talks are made available to attendees shortly after each talk ends.

Live captioning is high on our priority list for summer 2021!

Preparing and uploading a video to Clowdr

The following 6-minute video will guide you through the process of uploading your video and editing the auto-generated captions:

The process is also outlined in the following step-by-step instructions:

  1. Invitation to upload

    You will receive an email from the conference organizer (via Clowdr) requesting you to upload your video(s) to the platform. This email will include a direct link to the upload page. There is no need to log in!

  2. Upload video

    Once you’ve landed on the upload page via the link in the request email, you will be able to drag-and-drop a file or click the upload button to browse files on your device and add your video.

    Please note: You are given three attempts to submit your video. This page will also include information on the maximum duration and quality of the video.

  3. Confirmation email

    Once you’ve uploaded a video, you will receive an email from Clowdr confirming your submission was received and is being processed.

  4. Processing and captioning

    This will be followed by two additional emails - one marking when your video has been processed, and a final email confirming that it has been captioned and is ready for viewing & editing. Please remember to check your spam folders for communications from Clowdr.

  5. Auto-generated subtitles

    Clowdr will auto-generate the subtitles for your video - this typically takes 5 to 20 minutes, but can sometimes take longer. If you have not received any communications from Clowdr with the status of your video after 4 hours, please contact your conference organizers for technical assistance.

  6. Edits to captions

    Once you receive the email confirming that your captions are ready for review, follow the link in the email to edit them. The space to enter modifications will be presented alongside the video. You can input edits by simply clicking the text you want to modify and typing directly into the body of the transcript.

  7. Saving edits

    Please remember to click the Save button on the right hand side of the screen before exiting or reloading the page, to save and submit any changes. Failing to click Save will result in lost edits!

Taking the time to curate subtitles helps to ensure all attendees in all environments are able to enjoy your video. Thank you!

Uploads: technical details

Clowdr supports a wide range of video upload formats. However, for the best results, we recommend that you upload videos in the following format:

  • Codec: H.264 (AVC)
  • Container: MP4
  • Resolution: 1920x1080 (1080p)

Note: Clowdr does not support the following H.264 profiles: High 4:2:2, High 10-bit, High 4:4:4. Files produced in a ‘lossless’ mode are unlikely to work.

Tip: you can use the following ffmpeg command to convert many input videos to a format Clowdr accepts.

ffmpeg -i <input file> -vcodec h264 -s hd1080 -crf 23 output.mp4


© Clowdr CIC 2021

Clowdr is a social enterprise dedicated to creating sustainable, inclusive and engaging conferences.

Clowdr is a UK Community Interest Company, number 12984216.

Clowdr was initially made possible thanks to support by the US National Science Foundation under awards CCF-2035003, CCF-2035101 and CCF-203500 and support from