Video and subtitle guide: frames, WebM clips and timing
Extract frames, inspect video, trim or mute supported WebM, and convert SRT or WebVTT subtitles. Check keyframe boundaries and subtitle offsets before delivery.
Choose an operation for your task
Extract frames, inspect video, trim or mute supported WebM, and convert SRT or WebVTT subtitles. Check keyframe boundaries and subtitle offsets before delivery.
| Your task | Where to start |
|---|---|
| Create a cover image | Extract a frame and inspect the saved PNG |
| Trim a short clip | Use supported WebM; a compatible browser can keep one supported Opus track, otherwise choose Video only and compare the keyframe range |
| Adjust subtitle synchronization | Shift a small sample first, then check the first and last cue |
Work in order and retain the original
Inspect the source first and test a short clip. Keep subtitles beside the video and shift a copy when the lead-in changes. Plain SRT and WebVTT conversion must preserve cue text and duration; unsupported styling or region blocks should be rejected, not silently discarded. Negative cue times are a signal to revise the offset.
A cue from 1.000 to 3.000 seconds shifted by +1.5 seconds becomes 2.500 to 4.500 seconds; its duration stays two seconds.Separate processing success from acceptance
A partial cut can keep one supported Opus track by re-encoding audio locally in a compatible browser; unsupported Opus layouts, multiple audio tracks and Vorbis require Video only, which removes all audio tracks. Play and listen to the output, check the saved range and first and last subtitle cue. Trimming does not imply universal codec conversion.
Before you finish
Expand a tool below for its steps, options and limits. Choose the tools needed for your task; you do not need to use every one.
- Play the output, listen for sync and check the first and last cue. Removing a track or trimming a file does not imply universal codec conversion.
- Reopen the download and compare it with the example and the meaning of the input.
- When an input exceeds the stated boundaries, retain it and split the task or use a suitable processor; renaming an extension does not make it compatible.
References
- Video — format and implementation reference
Reference for format and processing boundaries. The operating reference states the actual supported scope of this site.
Tools in this category
Expand a tool to see its steps, options and supported formats, then open its workspace.
Save a video frameCapture a still image from a video and save it as PNG.
Choose a moment in a local video, preview it, and save the browser-decoded picture as a PNG at the source video's dimensions.
Steps
- Choose a video that plays in your browser. The file stays in this tab.
- Play or scrub to the moment you want, use the current playback position, or adjust the slider or seconds.
- Select Extract frame. Check the image and its dimensions, then download the PNG.
Available options
- Frame time (seconds)
- 0
Capabilities and limits
- One local video up to 50 MiB. The browser must be able to decode it; frame-accurate seeking is not guaranteed for every codec.
Video informationInspect video duration, resolution, codecs, frame rate and file size.
Inspect the technical fields stored in a local video without uploading it: duration, encoded dimensions, container, video and audio codecs, frame rate, bit rate and file size where reported.
Steps
- Choose a local video. Its working bytes stay in your browser.
- Select Read video information and review the duration, resolution and available track details.
- Copy the readable summary or download the JSON report for your records.
Capabilities and limits
- One local video up to 50 MiB and 128 video/audio tracks in total. The selected technical fields for every supported video and audio track are included in the complete JSON; fields are not limited to the first eight tracks. The JSON is limited to 8 MiB; a file exceeding either report limit is rejected as a whole.
- Common MP4, MOV, WebM, MKV and AVI containers can be inspected. Unsupported or missing measurements are shown as unknown; subtitle and menu tracks are not inventoried. This report does not test playback.
Mute videoRemove every audio track from supported MP4 and WebM videos without re-encoding the picture.
Save a new video with its audio tracks physically removed. Supported H.264 MP4 and VP8, VP9 or AV1 WebM video packets are copied without re-encoding; this does more than mute playback.
Steps
- Choose an MP4 or WebM file; preview its picture and sound if your browser supports the codec.
- Select “Remove audio tracks” to save the video stream in a new file.
- Compare playback when available, then download and check the new video in your intended app.
Capabilities and limits
- One local video, up to 50 MiB and 60 seconds. MP4 requires one H.264/AVC video track; WebM requires finite clusters and one VP8, VP9 or AV1 video track. Unsupported codecs, encrypted video and other containers are rejected.
Trim videoTrim supported WebM video and review its actual export range.
Preview a WebM video and choose the part to keep. The actual start moves back to the previous video keyframe. Keep sound re-encodes a supported single Opus track locally for partial clips; Video only removes every audio track.
Steps
- Choose a local .webm file and preview it in your browser.
- Play or scrub to mark the start and end, or type the times in seconds. Leave end blank to keep the rest; the saved clip may begin before the chosen start.
- Choose Keep sound or Video only. A supported Opus partial cut re-encodes audio in your browser; if the file or browser cannot do that safely, choose Video only to export the same picture range without sound. Preview and listen to the result before downloading.
Available options
- Start (seconds)
- 0
- End (seconds; blank = rest)
- Enter as needed
- Audio in saved clip
- Keep sound · Video only — remove audio
Keep sound is the default. Partial cuts with one supported Opus track re-encode audio locally; if this file or browser is unsupported, choose Video only to remove audio.
Capabilities and limits
- Local video is limited to 50 MiB; finite-cluster WebM with VP8/VP9/AV1 video and optional Opus/Vorbis audio can export up to 60 seconds. Partial cuts can keep one supported Opus track when this browser supports local audio re-encoding. Vorbis, multiple audio tracks and unsupported Opus layouts require Video only, which removes all audio tracks.
Subtitle conversion and timingConvert plain SRT and WebVTT cues and shift their timing with millisecond precision for a changed video lead-in.
Convert plain SRT and WebVTT subtitles and shift every cue by an exact millisecond offset. Choose pasted text or one UTF-8 subtitle file, then download a new SRT or WebVTT file.
Steps
- Choose pasted subtitles or one UTF-8 SRT/WebVTT file. Keep the original.
- Choose SRT or WebVTT output and an offset in seconds with up to three decimal places; positive delays cues and negative advances them.
- Check the cue count and first/last times, then reopen the downloaded subtitle file in the target player.
Available options
- Output format
- SRT · WebVTT
- Time offset (seconds)
- 1.5
Positive values delay subtitles; negative values bring them forward. For example, 1.5 delays them by 1.5 seconds.
Capabilities and limits
- Up to 10,000 plain cues; offsets must be whole milliseconds within ±24 hours. Negative or reversed timings and unsorted starts are rejected. WebVTT cue identifiers and settings, NOTE, STYLE, REGION, rich tags and character references are unsupported rather than silently lost.
- Text stays in the browser. Pasted input is limited to 1 MiB; one UTF-8 .srt, .vtt or .txt file is limited to 10 MiB. The output does not overwrite the original.