Convert video to MP4
Free, no sign-up, and nothing is uploaded.
Worked example
MP4 with H.264 is the safe answer whenever you are not sure what will play the file.
| Extension | .mp4 |
|---|---|
| MIME type | video/mp4 |
| Playback | Plays everywhere |
| From MP4 without re-encoding | Yes |
| Video codec | libx264 |
| Audio codec | aac |
The equivalent command
ffmpeg -i holiday-clip.mp4 -c:v libx264 -crf 23 -pix_fmt yuv420p -preset veryfast -c:a aac -b:a 160k -movflags +faststart -threads 1 -y out-holiday-clip.mp4This is exactly what runs in the browser. Copy it to run the same job locally on a file too large for a tab.
What to expect
Size is only predictable when you set a bitrate. These figures are for the bitrate example above:
| At 1500 kbps for 60s | 12.1 MB |
|---|---|
| Rough encode time | 5:38 |
At a constant quality the encoder lets the bitrate follow the content, so the output size genuinely cannot be predicted in advance — a slide deck and handheld footage of leaves differ by an order of magnitude at the same setting.
Why it matters
Two details decide whether an MP4 actually plays everywhere. The pixel format has to be yuv420p, or x264 may choose a 4:4:4 profile that Safari and most hardware decoders refuse. And the index has to be moved to the front of the file with faststart, or a browser cannot begin playing until the last byte has arrived. This tool sets both without being asked.