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Subtitles and media

Fix subtitle timing and prepare media previews

Written by CovertonPublished Updated

Adjust subtitle timing when captions drift from a video, then check the actual playback. Format conversion and reading transcripts are separate tasks. Video thumbnails and audio waveform images provide previews rather than full video editing.

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Timing is scaled before the offset

The timing tool first multiplies each subtitle start and end time by the chosen factor, then adds the time offset. An output time below zero, or a start time later than its end time, causes an error. Check speech and subtitles near the beginning, middle and end of the video.

Review SRT/VTT conversion and warnings

Input supports UTF-8 text SRT/VTT files up to 5 MB. VTT position and style settings are omitted in SRT. Quality inspection reports potential problems without editing cues, so review intentional overlaps against the video.

Create transcripts and preview images

Transcript output follows cue order and removes tags and styling. Video thumbnails save selected scenes as images; audio waveforms visualize sound. Media requires browser-supported codecs. These tools do not automatically transcribe speech.

Choose the right tool

Example inputs illustrate the workflow; they do not promise a particular file size, recognition accuracy or compatibility.

Create an audio waveform image

Visualize audio amplitude for reference or documentation. This is not speech transcription.

Example

supported audio → waveform image
  1. Choose files in MP3, WAV, M4A, OGG, FLAC, AAC format. Maximum files per batch: 1.
  2. Review Width (px), Height (px), Background color, then start processing.
  3. Download the PNG result and check its content and quality.
What to check

The browser must decode the audio codec. A waveform shows amplitude, not a frequency spectrum or transcript.

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Extract a video thumbnail

Save a frame from a playable video as a cover image. Compare the selected time with the exported frame.

Example

video + selected timestamp → frame image
  1. Choose files in MP4, WEBM, MOV, M4V format. Maximum files per batch: 1.
  2. Review Frame time (seconds), Output format, Output quality (%), then start processing.
  3. Download the JPGPNG result and check its content and quality.
What to check

Browser seeking is not guaranteed to be frame-accurate. The source codec must be supported.

Open the tool →

Subtitle sync

Adjust subtitle offsets or timing scale and verify synchronization near the start, middle and end.

Example

SRT/VTT cues + timing adjustment → retimed subtitlesOpen the tool →

Subtitle checker

Find potential overlaps, long lines and fast reading rates, then review them against the video before editing.

Example

SRT/VTT → timing/readability issue reportOpen the tool →

Subtitle converter

Convert text subtitles for an SRT or VTT player. VTT positioning and styling are not preserved in SRT.

Example

captions.vtt → captions.srtOpen the tool →

Subtitle transcript

Read subtitle content as a transcript without cue times or tags. This does not transcribe audio.

Example

SRT/VTT cues → reading transcript.txtOpen the tool →

This guide describes the public web tools and their support limits. Keep your original and check the downloaded result. Coverton · Corrections and contact