A video can have the right picture and still fail at the destination because its container, codec, resolution, or audio track is incompatible. Use the converter above to choose an MP4 or WebM output, keep the existing codec when it fits, or re-encode with a measured quality or file-size goal.
Processing runs in the browser on the current SocialPageAtlas tool. You can add up to five videos, with a current limit of 512 MB and 30 minutes per file. Browser and device encoder support varies, so the available choices on your screen are the authoritative list for that device.
How to convert a video online
- Add a video. Drag a file onto the tool, browse your device, or paste when your browser supports it.
- Choose the destination format. Select Keep codec, an MP4 option, or a WebM option based on where the file must play.
- Choose the size and quality method. Use Smart for measured similarity, Target size for a delivery limit, or Manual bitrate for a fixed encoding rule.
- Set resolution and frame rate. Leave them unchanged unless the destination or file-size goal requires a reduction.
- Decide whether to keep audio. Remove it only when the destination does not need sound.
- Convert, review, and download. Play the result from start to finish before deleting the source.
Container and codec are different decisions
MP4 and WebM are containers: they organize video, audio, timing, and metadata into a file. H.264, H.265, VP8, VP9, and AV1 are codecs: they describe how the video stream is compressed. A player must understand both. The WebCodecs video concepts guide explains why one container can hold more than one codec.
| Choice | Start here when | Trade-off to check |
|---|---|---|
| Keep codec | The existing video codec is valid in the requested container | Fast and lossless for the picture, but it cannot fix an unsupported codec |
| MP4 + H.264 | Broad playback compatibility is the priority | May be larger than newer codecs at similar visible quality |
| MP4 + H.265 | A modern destination explicitly accepts HEVC | Encoding and playback support depend on device and licensing stack |
| MP4 + AV1 | A modern workflow accepts AV1 in MP4 | Encoding can be slower and hardware support is not universal |
| WebM + VP9 | The file is intended for a modern web workflow | Some editing or messaging applications prefer MP4 |
| WebM + AV1 | Delivery efficiency matters and the destination is tested | Older devices may not decode it smoothly |
| WebM + VP8 | A legacy WebM workflow requires VP8 | It is less efficient than newer alternatives |
When the converter can copy instead of compress
If the source already contains a codec that the chosen container accepts, the tool can move that compressed stream into the new container without decoding and encoding the picture again. This is commonly called remuxing. It preserves the existing encoded frames and is usually much faster.
Changing the codec, resolution, frame rate, or other stream properties forces a re-encode. Re-encoding can reduce size or improve compatibility, but most delivery codecs are lossy. Keep the original if the file may be edited again.
Smart, Target size, or Manual bitrate?
| Mode | Best use | What to verify |
|---|---|---|
| Smart | Find a lower bitrate that stays above the selected SSIM threshold | Inspect text, faces, motion, gradients, and scene changes |
| Target size | Meet a known upload or messaging limit | A very small target may require lower resolution or visible loss |
| Manual bitrate | Apply a known delivery specification | The same bitrate does not suit every resolution or type of motion |
The current Smart presets range from Maximum to Smallest and use sampled segments to choose a bitrate before encoding the full video once. SSIM is a repeatable similarity measure, not a guarantee that every important detail is protected. Review demanding scenes at normal speed and pause on fine detail.
Reduce file size in the order that costs least
- Keep the existing stream when only the container must change.
- Remove audio only if the destination does not need it.
- Limit resolution to the real delivery size.
- Lower frame rate only when motion remains acceptable.
- Then reduce bitrate or choose a stronger compression preset.
Resolution often has the largest effect on phone footage because it reduces the number of pixels encoded in every frame. Frame-rate reduction can save additional data, but it changes motion. A target that looks acceptable for a talking head may fail on gameplay, confetti, water, or handheld movement.
Local processing, performance, and privacy
The live tool states that files are read, decoded, encoded, and written inside the page without an upload endpoint. It uses browser-native encoding capabilities such as the WebCodecs API, which can use hardware acceleration when the device exposes it.
Local processing means the result depends on your browser, operating system, available codecs, memory, and hardware. Keep the tab open, prevent the device from sleeping, and process fewer files at once if the browser becomes memory constrained.
Troubleshooting conversion failures
| Problem | Likely cause | Next action |
|---|---|---|
| An output option is missing | The browser or device does not expose that encoder | Choose an available codec or retry in a current browser on supported hardware |
| Keep codec is unavailable | The existing stream is not valid in the selected container | Choose a compatible re-encode option |
| The result is larger | The chosen quality, resolution, or codec costs more than the source | Use Target size, lower dimensions, or retain the source |
| Playback has no sound | Audio was removed or its codec is unsupported at the destination | Convert again with audio enabled and test the receiving app |
| Processing stops | The tab lost resources, the device slept, or the source is unsupported | Keep the tab active, reduce batch size, and try a broadly supported source |
Convert for the player that must open the file
Start with the destination specification, preserve the stream when possible, and change only the variables that solve a real compatibility or size problem. For still images, use the online image converter. For other browser-based production utilities, open the SocialPageAtlas toolbox.