Online MP4 Player
Play MP4 videos straight in your browser - drag, drop and play. Built-in codec inspector, subtitle loader and converter for MP4 files your browser cannot decode.
100% local, nothing uploaded
Instant HTML5 playback
Fix unplayable MP4s
Drop your MP4 file here
or click to browse - file is processed locally, never uploaded
MP4
M4V
MOV
WEBM
MKV
3GP
AVI
TS
or paste a URL
Codec Inspector
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Convert to H.264 MP4
Re-encode any video to a universally compatible H.264 + AAC MP4 - playable in every browser, on every phone and in every editor. Conversion runs entirely in your browser using FFmpeg.wasm. Large or 4K files will be slow.
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Which MP4 Codecs Play in Which Browser?
An MP4 is just a container. Whether it plays depends on the video and audio codecs stored inside it. This table covers the codecs you are most likely to find in an MP4 file.
| Codec inside MP4 | Chrome | Edge | Firefox | Safari |
|---|---|---|---|---|
| H.264 / AVC | Yes | Yes | Yes | Yes |
| AV1 | Yes | Yes | Yes | HW only |
| HEVC / H.265 | HW only1 | HW only1 | No | Yes |
| MPEG-4 ASP (Xvid/DivX) | No | No | No | No |
| AAC audio | Yes | Yes | Yes | Yes |
| AC-3 / DTS audio | No | HW only | No | macOS |
- HEVC in Chrome and Edge needs an HEVC-capable GPU; on Windows the HEVC Video Extensions must also be installed. See the HEVC hardware support guide.
- When a file fails, the most common cause is an unsupported codec inside a perfectly valid MP4 - the Convert button above re-encodes it to H.264 + AAC.
My MP4 File Won't Play - What Now?
If an MP4 fails to load, the cause is almost always one of these:
- Unsupported video codec. The file is a valid MP4 but holds HEVC, Xvid, DivX or another codec the browser cannot decode. Use the Convert / Fix MP4 button to re-encode to H.264. For HEVC files specifically, the HEVC Player has a dedicated capability check.
- Unsupported audio codec. H.264 video paired with AC-3, DTS or MP2 audio will fail even though the video is fine. The Codec Inspector flags the audio codec above.
- Faststart / moov atom at the end. Some MP4s store their index at the end of the file, so progressive playback stalls. Re-encoding with this tool rewrites the file with the index at the front.
- Wrong extension. A file named .mp4 may actually be an AVI, MKV or FLV. The Codec Inspector reads the real container format above.
- Remote URL blocked by CORS. A pasted URL only plays if the host allows cross-origin requests. Download the file and drop it in instead.
For deeper diagnosis use the Codec Troubleshooter or run the file through the Codec Finder.
Frequently Asked Questions
Yes. It is free with no sign-up. All playback, codec analysis and conversion run locally in your browser using HTML5 and WebAssembly - your video files are never uploaded to any server. Only URLs you paste are fetched directly by your browser.
MP4 is a container, not a codec. A file can be a valid .mp4 but use a video codec the browser cannot decode - HEVC, MPEG-4 ASP (DivX/Xvid), H.263 - or an audio codec like AC-3 or DTS. The browser reads the MP4 wrapper but chokes on the stream inside. The Convert button re-encodes it to H.264 + AAC, which plays everywhere.
H.264 (AVC) plays in every modern browser. AV1 plays in current Chrome, Edge, Firefox and Opera, and on Safari with hardware support. HEVC (H.265) plays only where the device has a hardware decoder, mainly Safari and capable Chrome/Edge machines. Older MP4 codecs like Xvid and DivX do not play in any browser without conversion.
Yes. Load an external .srt or .vtt file and toggle it on or off. SRT is converted to WebVTT automatically in your browser. Subtitles embedded inside the MP4 are not extracted by the browser, so load them as a separate file.
Re-encoding is lossy, but at the default Balanced quality (CRF 23) the difference is hard to notice for most footage. Choose High (CRF 20) for the closest match to the source, or a higher CRF for a smaller file. There is no way to losslessly change the video codec - that always requires a re-encode.
Browser-based conversion is single-threaded and slower than desktop tools. Expect roughly real-time speed for 1080p and 3-5x real-time for 4K. For long files use the Trim option, or for unattended jobs use a desktop tool like XMedia Recode or FFmpeg Batch AV Converter.
Playback has no fixed limit because the file streams from your own disk. Conversion is bounded by your device memory - FFmpeg.wasm processes the file in RAM, so very large 4K files can run out of memory. Trim long files first, or use a desktop converter for big jobs.
More Free Online Tools
About This Online MP4 Player
MP4 is the most common video format in the world - used by phones, cameras, editors and every streaming service. This free online MP4 player lets you play MP4 files directly in any browser without installing anything, and without uploading your video anywhere.
The tool runs entirely on your device. Drop a file in and it detects the container, video codec, profile, bit depth, resolution, framerate and audio codec, then plays the file with native HTML5 video. If your browser cannot decode what is inside the MP4 - for example an HEVC or Xvid stream - the Convert button transcodes it to H.264 + AAC using FFmpeg.wasm, producing a file that plays everywhere.
Common use cases include playing a downloaded MP4 that silently fails, checking the real codec inside a file before publishing, previewing footage with external subtitles, grabbing a still frame, and rescuing recordings whose audio codec the browser refuses to play.
Desktop MP4 Players & Codec Tools
For long files, 4K content or hardware-accelerated playback, a desktop player is faster than any browser. VLC Media Player, MPC-BE, MPC-HC and mpv player all play MP4 with any codec inside, using hardware acceleration on supported GPUs.
To enable MP4 codecs system-wide on Windows, install the K-Lite Codec Pack. For batch converting MP4 files to H.264, HEVC, AV1 or other formats, XMedia Recode and FFmpeg Batch AV Converter handle multi-file queues with full codec control. Windows users can also browse the codec database or run files through Codec Inspector for detailed analysis.
