convert outputs with empty subtitles

Question

We have created a Media Convert job with two audio tracks and three subtitle tracks. The job definition is the attached JSON.
When playing the convert result in VLC or JW Player, the video and audio qualities and the 3 types of subtitles appear, but when clicking on any subtitle, nothing appears. In S3 the 3 subtitle files appear, but they are empty.
[https://drive.google.com/file/d/1Gk_2FxdS98VTP3kPl_3yvNIrELHDEU9M/view?usp=sharing]()
![Enter image description here](/media/postImages/original/IMBdJbxlp_SHe8UjwcgEw5wg)

Answer

Reviewing your job config, it seems you are using 3 separate WebVTT file sources. If the 3 output CC files are being generated, yet contain no information, it may be related to the TimeCode alignment of the video source and the WebVTT captions sidecar files. 
You could run a quick test using, CC Burn-in as the CC output format, with each WebVTT source. (Use clipping do only run an 3-5min job). If the TimeCodes are misaligned you won't see CC burned in.

Please check the CC sidecar output format being selected when creating the CMAF container. (Are they separate sidecar files or included in the CMAF wrapper?) Please see the following list for CC formats supported for output formats.
https://docs.aws.amazon.com/mediaconvert/latest/ug/sidecar-captions-support-tables-by-container-type.html

convert outputs with empty subtitles

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