FormatDrop
How-To Guide

How to Convert AVI to MP4 (Free, Fast, No Software Needed)

AVI (Audio Video Interleave) was created by Microsoft in 1992 and was the dominant video format for over a decade. You'll find AVI files on old camera recordings, digitised VHS tapes, older CCTV footage, and archives from pre-2010 video content. The problem: AVI isn't supported by modern mobile devices, streaming platforms, or web browsers. Converting AVI to MP4 makes your video playable on everything — phone, TV, social media, cloud storage, everywhere.

Open AVI to MP4 Converter

Step-by-step instructions

  1. 1

    Open FormatDrop video converter

    Go to formatdrop.com/avi-to-mp4. This converter uses FFmpeg compiled to WebAssembly and runs entirely in your browser — no software download, no file upload to a server. Works on Windows, Mac, Linux, and mobile browsers.

    Go to converter
  2. 2

    Upload your AVI file

    Drag your AVI file onto the converter or click to browse. AVI files can use many different video codecs internally — DivX, Xvid, MPEG-2, MPEG-4, H.264, and others. The converter handles all common AVI codecs automatically. If the AVI uses a rare or proprietary codec, you may see a processing error — in that case, VLC media player can also convert AVI files via Media → Convert/Save.

  3. 3

    Choose H.264 MP4 for best compatibility

    Select MP4 as output, H.264 as the video codec, AAC as the audio codec. This combination plays on every device made in the last 15 years. If the source AVI is very large and you want smaller output, H.265 gives 30–50% smaller files but requires modern devices to play smoothly.

  4. 4

    Select quality settings

    For archival: use CRF 18 (near-lossless for H.264) or match the source bitrate. For casual playback: CRF 23 (H.264 default, excellent quality). For file-size-constrained sharing: CRF 28 (acceptable quality, significantly smaller). Lower CRF number = higher quality = larger file.

  5. 5

    Convert and download

    Click Convert and wait for processing. AVI-to-MP4 conversion time depends on the video length and codec — for a simple container change (where the AVI contains H.264 video), conversion may be near-instant. If re-encoding is required (DivX, Xvid, old MPEG-4 source), expect roughly 1× real-time processing. Download the MP4 when done.

Why convert AVI to MP4?

AVI is actually a container format, not a codec — it can hold many different video codecs inside it. This is why some AVI files are tiny and others are huge, and why some play correctly while others have missing audio or video. The most common AVI codecs from the 2000s era are DivX and Xvid (both MPEG-4 Part 2 variants), which predate H.264 and are far less efficient. A 2-hour movie in DivX AVI might be 1.4 GB; the same movie in H.264 MP4 could be 700 MB at the same visual quality. Beyond file size, AVI has structural limitations: it doesn't officially support modern audio formats (like AAC), it doesn't support variable frame rate video (common in screen recordings and smartphone videos), and it has no native support for subtitles. MP4 handles all of these. Converting AVI to MP4 doesn't just change the container — when re-encoding, it upgrades the video codec from an early-2000s standard to a modern one, dramatically improving compatibility and often reducing file size.

Your files never leave your device

FormatDrop runs the conversion engine entirely inside your browser using WebAssembly. No file upload. No server. Nothing stored. You can verify this by opening DevTools → Network tab and watching: zero upload requests.

Frequently asked questions

Will converting AVI to MP4 reduce quality?
If re-encoding is needed (when the AVI contains DivX, Xvid, or other codecs that differ from H.264): yes, there's some quality loss, but at CRF 18–23 it's imperceptible in normal viewing. If the AVI already contains H.264 video, the converter can remux (copy) the video stream without re-encoding — zero quality loss, near-instant conversion. The audio almost always needs re-encoding from MP3/PCM to AAC, which at 192 kbps is inaudible.
Why won't my AVI file play on my phone?
AVI is not supported natively by iOS or Android. iPhones don't support AVI at all — you must convert to MP4 first. Android phones support AVI to varying degrees depending on the version and device manufacturer, but it's unreliable. Convert to MP4 H.264 for guaranteed playback on any phone.
How do I convert AVI to MP4 on Windows without software?
FormatDrop runs directly in Chrome, Firefox, or Edge — no installation needed. Alternatively, Windows 10/11 includes the 'Photos' app which can do basic video export, and VLC (free) can convert AVI to MP4 via Media → Convert/Save. For a completely no-install option, the browser-based FormatDrop is the fastest route.
Why is my converted MP4 larger than the original AVI?
This can happen if the AVI was heavily compressed (old DivX files were often compressed to very low bitrates like 700 kbps) and the MP4 is being encoded at a higher quality CRF. The converter targets quality, not a specific bitrate — so if the AVI was very low quality, the MP4 may actually be a better quality file and thus larger. To match or reduce file size: explicitly set a target bitrate or use a higher CRF value (e.g., CRF 26–28).
Convert AVI to MP4 Now — Free

No account. No upload. Works in any browser.

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