AVI to MP4
AVI is a Windows-era video container from the 1990s that still shows up in old camcorder footage, screen recordings, and archived clips. The problem is that AVI files are big, often use dated codecs, and don't play cleanly on phones, browsers, or streaming platforms. MP4 fixes all three: modern H.264 compression shrinks the file dramatically while keeping the same visual quality, and virtually every device on earth plays it. Converting AVI to MP4 re-encodes the video into an efficient modern codec, so a bulky AVI can drop to a fraction of its size. FluidConvert handles the conversion in your browser, free, with no account, no software install, and no watermark, turning legacy AVI clips into files you can actually share and stream today.
Drop your file here, or browse
Accepts: video/x-msvideo, .avi · Max 1GB · always free
Your files are encrypted with TLS and automatically deleted after conversion.
Simply upload your .AVI file and we'll convert it to .MP4 format — fast, free, and secure.
Fast & Free
Convert files up to 1GB completely free. No account, no limits.
Secure
Files are encrypted and automatically deleted after conversion.
High Quality
Industry-leading conversion with no quality loss.
How to Convert AVI to MP4
Upload Your File
Click the upload area above or drag and drop your .AVI file. We support files up to 1GB, completely free.
Choose Output Format
Select .MP4 as your target format. Adjust any conversion settings if needed.
Download Your File
Click Convert Now and wait a few seconds. Once complete, download your converted file instantly.
About AVI to MP4
Last updated: August 2026
What is AVI?
AVI (Audio Video Interleave) is a container format Microsoft introduced in 1992 as part of its Video for Windows technology. It interleaves audio and video data in chunks and can hold a variety of codecs, from old DivX and Xvid to uncompressed streams. For its era it was groundbreaking, and it became the default format for early digital camcorders, screen capture tools, and downloaded clips. But AVI is showing its age: it lacks native support for modern features like efficient streaming, chapter markers, and soft subtitles, and files tend to be large because they often use older, less efficient codecs or minimal compression.
Why convert to MP4?
MP4 with H.264 video is the modern standard for a reason. It compresses far more efficiently than the codecs commonly found in AVI files, so the same footage takes up much less space at comparable quality. MP4 also plays natively on smartphones, browsers, smart TVs, and every major social and streaming platform, none of which reliably handle AVI. Converting to MP4 makes an old clip small enough to email or upload and compatible enough to play anywhere. It is the practical way to bring legacy AVI footage into modern workflows without dedicated playback software.
What to expect from the conversion
AVI to MP4 is a re-encoding conversion, not a simple rewrap, because AVI files rarely contain codecs MP4 can copy directly. The video is decoded and re-compressed with H.264, which is lossy: a small amount of detail is discarded during compression. In practice, at sensible quality settings the difference is hard to notice, and the payoff is a much smaller file, often a fraction of the original AVI size, thanks to H.264's superior efficiency. Audio is typically re-encoded to AAC. The result plays smoothly on modern devices where the source AVI would have stuttered or failed to open.
How FluidConvert handles it
Your AVI is decoded and re-encoded to H.264 MP4 on secure servers tuned to preserve visual quality while cutting file size. All uploads are encrypted in transit and automatically deleted from our servers roughly an hour after processing. There is no watermark, no signup, and no charge.
Common reasons to convert AVI to MP4
- Converting old camcorder or webcam AVI footage into small MP4 files you can store and back up easily
- Making a legacy AVI clip playable on an iPhone, Android phone, or in a web browser
- Shrinking a bulky AVI screen recording so it is small enough to email or upload
- Preparing archived AVI videos for YouTube, which processes MP4 far more reliably
- Importing an old AVI into modern editing software that no longer supports DivX or Xvid codecs
Frequently Asked Questions
Why is my MP4 so much smaller than the original AVI?
AVI files often use older codecs like DivX, Xvid, or lightly compressed streams that are far less efficient than H.264. When FluidConvert re-encodes to MP4 with H.264, the same footage is compressed much more effectively, so file size can drop to a fraction of the original with little visible quality difference. The size reduction is a benefit of the modern codec, not a sign that the video was degraded.
Is converting AVI to MP4 lossy?
Yes. Because AVI codecs generally can't be copied straight into an MP4 container, the video is decoded and re-encoded with H.264, which discards some data during compression. At reasonable quality settings the loss is visually negligible for most footage. It is technically lossy, so you won't gain quality, but you gain broad compatibility and a much smaller file.
Why won't my AVI file play on my phone or in my browser?
Modern phones and browsers dropped native support for AVI and the older codecs it usually contains, like DivX and Xvid. The file may show an unsupported-format error or play with no sound or no picture. Converting to MP4 with H.264 video and AAC audio produces a file those devices decode natively, so it plays without installing any extra media player.
Will the audio stay in sync after converting AVI to MP4?
Yes. FluidConvert preserves the timing relationship between the audio and video during re-encoding, so lip sync and sound effects line up in the MP4 exactly as they did in the source. Some very old AVI files with variable frame rates can be tricky, but the conversion normalizes timing so the output plays smoothly on modern players that expect consistent timing.
Can I convert a large AVI file from an old camcorder?
Yes, and it is one of the best reasons to convert. Old camcorder AVI files are typically large and use dated codecs. Re-encoding to MP4 dramatically shrinks them while keeping the footage watchable, making decades of home video easy to store, back up, and share on modern phones and cloud services that never would have played the original AVI.