MP4 to MP4 Converter
An MP4 that refuses to play is usually not a bad file but the wrong contents inside a familiar box. This page rewrites the video as H.264 with AAC sound, the pairing every phone, browser, TV and editor decodes.
Video Converter
or drop MP4, MOV, MKV … files here ·
Max 95 MB per file· Up to 20 files· Deleted after 30 minutes
Files are processed on our servers and deleted after 30 minutes.
Lower is better quality and a bigger file. 18 looks identical to the source, 23 is the default, 28 and above shows visible softening.
Frames per second. Keep the source rate unless a platform asks for a specific one; 15–20 fps is plenty for GIFs.
Only used for PowerPoint files and single still images: how long each slide or picture stays on screen.
Auto uses AAC for MP4/MOV and Opus for WebM. Copy keeps the original sound untouched when the new format supports it.
192 kbps is transparent for music; 128 kbps is enough for speech.
Width of the animation in pixels; height follows the aspect ratio. 480 px suits chats, 720 px or more gives a high-quality GIF but a much larger file.
GIF holds at most 256 colors. Fewer colors make a smaller file but cause banding on gradients and skin tones.
Mixes palette colors in a fine pattern to hide banding. Sierra gives the smoothest result; none gives the smallest file.
Whether the animation repeats endlessly or plays one time and stops.
Optional. Seconds (e.g. 75) or minutes:seconds (1:15). Leave empty to start at the beginning.
Optional. Same format as the start time. Leave empty to keep everything up to the end.
The converted file will be at or just under this size.
How to use this tool
- 1
Add the MP4 that misbehaves
Drop it on the upload area or pick it from your device. Up to 20 videos per batch, each up to 95 MB.
- 2
Keep H.264 and quality 20
The page starts on Video codec H.264, Quality (CRF) 20 and AAC audio at 192 kbps. Lower the Resolution only if the file also has to get smaller.
- 3
Convert and download
Press Convert to MP4 and save the new file. Keep the original until the copy plays where you need it.
Why would anyone convert MP4 to MP4?
Because .mp4 says nothing about the codec inside. Re-encoding to H.264 video and AAC audio turns an MP4 that one device rejects into an MP4 every device plays, and fixes a slow-starting or oddly built file along the way.
Convert MP4 to MP4: same extension, different insides
MP4 is MPEG-4 Part 14, a container standardized by ISO in 2003 and built on Apple's QuickTime file layout. A container is only a wrapper: it holds a video stream, audio streams and an index that tells the player where each frame sits. Two files called holiday.mp4 can hold entirely different codecs, and a player that handles one may reject the other.
Since iOS 11 in 2017, iPhones record HEVC by default under Settings → Camera → Formats → High Efficiency, and many drones, action cameras and screen recorders do the same. Windows 10 and 11 play HEVC only after you buy HEVC Video Extensions in the Microsoft Store; older smart TVs and car head units not at all. Converting MP4 to MP4 rewrites the contents as H.264 video, AAC stereo audio and an index at the start of the file.
MP4 problems a re-encode fixes
"This file isn't playable" or error 0xc00d5212 in Windows Films & TV
The codec is HEVC or AV1. Convert with Video codec H.264 and it opens without a store extension.
Sound plays, picture stays black or green
A video codec the player lacks. Re-encode to H.264 and keep the audio settings.
Upload preview spins until the whole file has downloaded
The moov atom is at the end. The converted MP4 is written fast-start, with the index first.
Editor shows the wrong length or audio drifts out of sync
Variable frame rate from a phone or game capture. Set Frame rate to 30 or 60 fps.
TV or car screen says unsupported audio
The track is AC-3, E-AC-3 or Opus. Keep Audio codec on AAC for stereo sound every player accepts.
MP4
MPEG-4 video
MP4 (MPEG-4 Part 14) is a multimedia container standardised by ISO/MPEG and based on Apple's QuickTime format. It usually holds H.264 or HEVC video with AAC audio, and can also carry subtitles, chapters and metadata. It is the most compatible video format in the world, playing on phones, browsers, TVs, game consoles and social platforms. The video inside is almost always lossy, so repeated re-encoding gradually reduces quality.
- Compression
- Lossy
- Transparency
- –
- Animation
- –
- Introduced
- 2001 · Moving Picture Experts Group (MPEG)
MP4
MPEG-4 video
MP4 (MPEG-4 Part 14) is a multimedia container standardised by ISO/MPEG and based on Apple's QuickTime format. It usually holds H.264 or HEVC video with AAC audio, and can also carry subtitles, chapters and metadata. It is the most compatible video format in the world, playing on phones, browsers, TVs, game consoles and social platforms. The video inside is almost always lossy, so repeated re-encoding gradually reduces quality.
- Compression
- Lossy
- Transparency
- –
- Animation
- –
- Introduced
- 2001 · Moving Picture Experts Group (MPEG)
MP4 to MP4 is a repair job: the container is right but the codec, index or audio layout inside it is not, so you rewrite the contents and keep the name everyone recognizes.
Picking a CRF for an MP4 to MP4 re-encode
- CRF 14
Archive copy, often bigger than the source.
- CRF 18
No visible difference on a large monitor.
- CRF 20
This page's default, noticeably smaller.
- CRF 23
The general default, fine for messages.
- CRF 28
Soft grass, water and hair. Only for size caps.
CRF (constant rate factor) holds quality steady and lets the bitrate follow the scene. A step of about six roughly halves or doubles the file size. An HEVC clip re-encoded to H.264 at CRF 20 typically grows by a third to a half, because H.264 is the older, less efficient codec; that is the price of compatibility.
If the copy also has a size limit, lower the Resolution rather than pushing CRF past 26. Every other route to MP4, plus the full list of settings, is on the video converter page.
MP4 to MP4 converter questions
What does converting MP4 to MP4 actually change?
The extension stays the same, but the video and audio streams are written again. HEVC, AV1 or an unusual audio codec comes out as H.264 and AAC, with a fresh index. Picture size and frame rate stay as they were unless you change them.
Why does my MP4 play sound but show a black screen?
The player can read the audio but has no decoder for the video stream, almost always HEVC from a recent iPhone, drone or screen recorder. Re-encoding to H.264 removes the dependency; HEVC to H.264 covers that case in more depth.
Can an MP4 to MP4 converter fix a video that only starts after it has fully downloaded?
Yes. That delay means the index, the moov atom, sits at the end, so a browser must fetch everything before the first frame. The converted file is written with the index at the front, so playback starts while the rest loads.
My MP4 has two audio tracks. What happens to them?
The converted file carries one audio track, the one the source marks as default, re-encoded as AAC. For a phone, a TV or a social upload that is usually what you want, since a second commentary or language track can make some players pick the wrong one.
Does re-encoding the same MP4 several times make it worse?
Each lossy encode drops a little detail, so repeated passes slowly soften texture. One pass at CRF 18–20 is not visible in normal viewing. Always convert from the original, not from an earlier copy.
Can I make the MP4 smaller at the same time?
Yes. Pick a lower Resolution, such as 720p, or raise Quality (CRF) to 23–26. For a hard cap, tick Limit file size; compress video to 100 MB is set up for one common limit.
- HEVC to H.264 ConverterRe-encode HEVC (H.265) video as H.264 for smooth editing, direct play in Plex and older TVs. MP4, MKV or MOV output, original audio kept untouched.
- MP4 to H.264 ConverterConvert an MP4 holding HEVC, AV1, VP9 or old MPEG-4 video to H.264 AVC for upload forms, TVs and editors that require it. CRF 20 and AAC preset.
- Compress Video to 100 MBConvert a video to H.264 MP4 that is guaranteed to end at or under 100 MB, for GitHub, Google Forms and boosted Discord servers. Uploads up to 95 MB.
- MOV to MP4 ConverterConvert iPhone and QuickTime MOV videos to MP4 online. H.264 + AAC by default so the file plays on Windows, Android and every browser. 95 MB per file.
- MP4 to HEVC ConverterShrink H.264 MP4 videos by re-encoding them to HEVC (H.265) at CRF 28, the x265 default. Saves storage on phones, NAS drives and backups. No account.
- 1080p to 720p ConverterDownscale 1080p video to 720p MP4 to cut file size for email, slow uploads and older devices. Width follows the aspect ratio; never upscales. No account.