# Video encoding fails resulting in invalid captions format error in playback

Source: https://dev.arcxp.com/video-center/faq/video-encoding-fails-with-error-resulting-in-invalid-captions-format-error-in-playback/

## Symptoms

- Video fails with `Invalid captions format` during playback.
- Video Center clip failed to encode with error:  
`transcoder.m3u8vtt.postprocess`

## Cause

There is an illegal character in your clip’s closed captions that causes the error. All XML reserved characters including `" < > & '` should not be included in the `.vtt` file.

## Solution

1. Go to the video and confirm that the subtitle is failing. If you see the `Invalid captions format` error, this guide covers your scenario.
2. Get the video UUID.
3. Use curl to get the S3 subtitle path.

  - Remember to change “replace\_with\_uuid” in the URL.
  - The first time, you might need to install jq:  
  Terminal window  
  ```bash
  brew install jq
  ```
4. Look for the WEB\_VTT file (“url” is an S3 path).
5. In the WEB\_VTT file, look for any bad or illegal characters.
6. If you cannot find any and are still having issues, please submit an ACS ticket.