Run an AWS Transcribe batch job to produce SRT and VTT subtitle files

Steps

1. Upload your source audio or video file to an S3 bucket, then call 'StartTranscriptionJob' with 'MediaFileUri' pointing to the S3 object and 'LanguageCode' set to the spoken language (e.g., 'en-US')
2. Include a 'Subtitles' parameter in the StartTranscriptionJob request: set 'Formats' to an array containing 'srt', 'vtt', or both to generate subtitle files alongside the main transcript JSON
3. Set 'OutputStartIndex' to 1 in the Subtitles parameter if downstream tools expect 1-based cue numbering — AWS Transcribe defaults to 0-based indexing, which differs from standard SRT convention
4. Set 'OutputBucketName' and optionally 'OutputKey' to control where Transcribe writes the transcript and subtitle files — both the JSON transcript and the subtitle file(s) are written to the same S3 destination
5. Poll the job status by calling 'GetTranscriptionJob' with the job name until 'TranscriptionJobStatus' returns 'COMPLETED', then retrieve the subtitle file URIs from the 'SubtitleFileUris' field in 'SubtitlesOutput'
6. Download the SRT or VTT file from S3 using a presigned URL or the AWS SDK — subtitle files are written with the same key prefix as the transcript JSON but with a '.srt' or '.vtt' extension