Turn old AVI videos from cameras, phones and downloads into modern MP4 files that play on every phone, browser, TV and editing app. The conversion runs on your own computer with the ffmpeg engine, so your videos are never uploaded, and you can convert several files in one go.
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Conversion settings
Files
No files yet. Add one or more AVI videos above; you'll see their codec, size and length here before converting.
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How to use the AVI to MP4
Add your AVI files by dropping them on the box or clicking Choose AVI files. Each file shows its codec, size and length.
Pick the settings: Balanced quality and Fast speed suit most videos. Choose a smaller size to get smaller files.
Press Convert to MP4. The first time, the converter (about 31 MB) is downloaded and then cached by your browser.
Wait for the progress bar to finish. Keep the tab open; you can cancel at any time.
Press Download MP4 next to each file, or Download all (ZIP) for several files.
What's inside an AVI file?
AVI (Audio Video Interleave) is a container that Microsoft introduced in 1992. The container only holds the streams; the picture and sound inside can use many different codecs. That is why one AVI plays fine and another shows only sound or an error. When you add a file, this tool reads the AVI header and tells you which codecs it uses before anything is converted.
Video codec in the AVI
Typical source
What happens
Xvid / DivX (MPEG-4 Part 2)
Downloads and rips from the 2000s
Re-encoded to H.264
Motion JPEG (MJPG)
Digital cameras, webcams, dashcams
Re-encoded to H.264, file often becomes 5-10× smaller
DV
MiniDV camcorder captures
Re-encoded to H.264, much smaller
H.264
Newer cameras, screen recorders
Copied without re-encoding (Auto mode)
Uncompressed, Huffyuv, Lagarith, Ut Video
Capture cards, editing exports
Re-encoded to H.264, dramatically smaller
Choosing quality and speed
The quality setting is the x264 CRF value. CRF 23 is the encoder's default and a good balance; use 18-21 for archiving family videos and 27-30 when small size matters more than detail. The speed setting is the x264 preset: Fastest (ultrafast) finishes soonest but makes larger files, Slow (medium) makes the smallest files at the same quality but takes several times longer. Because the converter runs in a single browser thread, downscaling to 720p is the most effective way to speed up long HD videos.
The exact conversion
For re-encoded files the tool runs the equivalent of ffmpeg -i input.avi -c:v libx264 -preset veryfast -crf 23 -pix_fmt yuv420p -c:a aac -b:a 128k -ac 2 -movflags +faststart output.mp4, with your chosen values. The yuv420p pixel format and the fast-start flag make the MP4 play in every browser and start streaming immediately. Odd frame sizes are rounded to even numbers and non-square pixels (common in DV) are converted to square pixels so the picture keeps its shape.
Frequently asked questions
Is it safe to convert AVI to MP4 here?
Yes. The converter is the open-source ffmpeg engine compiled to WebAssembly and it runs inside your browser tab. Your videos are read from your disk and converted on your own computer; they are never uploaded to a server.
Will I lose quality converting AVI to MP4?
If the AVI already contains H.264 video, it is copied into the MP4 container with no quality loss at all. Other AVI codecs such as Xvid, DivX or MJPEG must be re-encoded to H.264. At Balanced (CRF 23) or High (CRF 21) quality the difference is very hard to see, and the MP4 is usually smaller than the AVI.
Why convert AVI to MP4?
AVI is an old container from the 1990s and most AVI files use codecs like Xvid, DivX or MJPEG that phones, web browsers, smart TVs and social networks do not play. MP4 with H.264 video and AAC audio is supported almost everywhere, so converting makes the video easy to watch, share and edit.
How long does the conversion take?
Copying H.264 takes seconds. Re-encoding runs on your CPU in a single thread, so a 480p video converts roughly in real time or faster, while 1080p can take a few times the video length. Choosing Fastest speed or a smaller size makes it quicker.
Is there a file size limit?
The browser gives the converter about 2 GB of memory for the input and output together, so files up to roughly 1 GB convert reliably and the hard limit is about 1.9 GB. For bigger files, use a desktop program such as HandBrake or ffmpeg.
What does CRF mean?
CRF (Constant Rate Factor) is the H.264 quality setting. Lower numbers mean better quality and bigger files: 18 is visually almost lossless, 23 is the standard default, and 28 or more gives small files with visible softening. Each step of about 6 roughly halves or doubles the file size.
Can I convert other formats too?
The converter also reads most other video files, such as WMV, FLV, MKV or MPG, and turns them into MP4 with the same settings. For converting between many formats use the Video Converter.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.