Free AVI to MP4 Converter: Rescue Old Videos Online

An AVI to MP4 converter decodes the old AVI file and re-encodes it as H.264 video with AAC audio inside an MP4 container, which plays on phones, smart TVs, browsers and store platforms. On AREM Labs you drop the AVI into the page, pick a quality level, press Convert and download the MP4; nothing is uploaded.

AVI is Microsoft’s container from the early 1990s. It is still everywhere in family archives, old screen captures, DV tape transfers and folders of DivX or Xvid files from the 2000s. The container itself is not the problem. The codecs inside it are: DivX, Xvid, Motion JPEG from old compact cameras, and raw DV from camcorders rarely play on an iPhone, inside a Shopify product gallery or in a modern browser. Changing the file extension does nothing. The picture has to be re-encoded. If you want the wider background on containers versus codecs first, the guide on how to convert video files for any device or platform covers every common format.

Free toolAVI to MP4 ConverterConvert legacy AVI videos into universal MP4 files right in your browser. Re-encode video using H.264 compression without uploading files to any server.Open the tool

How to convert AVI to MP4 step by step

The steps below use the AVI to MP4 Converter. It runs a WebAssembly build of a video engine inside your browser tab, so the file never leaves your computer.

1. Open the converter and drag your file onto the area labeled “Drop your AVI file here”, or click it to browse. The page accepts a single file of up to 1 GB.
2. Check the preview player that appears. If your browser cannot preview the AVI, that is normal for DivX and DV files; the engine can usually still decode them.
3. Pick a value under “Quality (CRF)”. The chips are High (18), Balanced (23), Small (28) and Smallest (32). A lower number keeps more detail and makes a bigger file.
4. Leave “Output format” on “MP4 (H.264) - most compatible”. The same menu also offers WebM, MOV, MKV and AVI if you need them later.
5. Press Convert. On first use the page downloads the video engine once (about 30 MB); the button shows that progress, then a processing percentage.
6. Watch the result in the preview, compare the new size with the source size shown next to the file name, and press Download.

In the current version the converter writes the MP4 at a width of 1,280 pixels and keeps the original aspect ratio, so a 640 x 480 AVI comes out as 1280 x 960. That keeps old clips at a size modern players handle well, but it can make a tiny source file larger. If size matters more than sharpness, choose Small (28) and check the result.

Free toolAVI to MP4 ConverterConvert legacy AVI videos into universal MP4 files right in your browser. Re-encode video using H.264 compression without uploading files to any server.Open the tool

What the MP4 file contains after conversion

It helps to know exactly what changes, because it decides where the file will play and how big it gets.

Property	Typical legacy AVI	MP4 from this converter
Video codec	DivX, Xvid, Motion JPEG, DV or uncompressed	H.264, 8-bit 4:2:0 (yuv420p)
Audio codec	MP3, PCM or AC-3	AAC at 160 kbps
Quality control	Fixed at recording time	CRF 18, 23, 28 or 32
Streaming layout	Index usually at the end of the file	Index moved to the front (fast start)
Playback on iPhone and Android	Often fails or needs an extra app	Plays in the built-in player
Input size limit in the tool	Up to 1 GB	Not applicable

The fast-start layout matters if you plan to put the clip on a website or a product page: the player can start before the whole file has downloaded.

How long does an AVI to MP4 conversion take?

Browser encoding runs on your own processor without server hardware, so expect it to take longer than the clip itself for anything above standard definition. A rough guide:

• Short standard-definition clips (a few minutes of 640 x 480 DivX) usually finish in a few minutes on a recent laptop.
• DV camcorder transfers are heavy. DV records at about 25 Mbps of video, so 1 GB holds only around four to five minutes of footage. Longer tapes need to be split before they fit under the 1 GB limit.
• Keep the tab in the foreground. Browsers slow down background tabs, which stretches the processing time.

If the result is still too large to email or upload, run it through the Video Compressor, which can aim at a target size in megabytes. If an old phone clip was recorded sideways, fix it afterwards with Rotate Video instead of re-recording anything.

AVI files the converter handles differently

Most AVI files convert without surprises, but three kinds need a moment of thought.

Interlaced DV and TV captures

Footage from DV camcorders and TV capture cards is often interlaced. The converter does not deinterlace, so fast motion can show thin horizontal comb lines on a progressive screen. For family archives this is usually acceptable; for professional reuse, deinterlace in an editing program before converting.

Files with several audio tracks

Some AVI rips carry two languages. The engine keeps one audio track in the MP4, normally the default one. If you need the other language, convert a copy with a desktop tool that lets you choose streams.

Batches of many AVI files

The page processes one file at a time. For a folder of mixed formats you can also use the general MP4 Video Converter, which accepts AVI, MOV, MKV, WebM, FLV and 3GP with the same settings. Sister guides show the same idea for other containers, such as the walkthrough on converting MKV to MP4 locally and the one on converting MOV to MP4 privately.

Common mistakes

• Renaming video.avi to video.mp4, which leaves the DivX or DV stream untouched and produces a file most players refuse; convert it properly so the video is re-encoded to H.264.
• Choosing Smallest (32) for archive footage, which adds visible blocking to already soft old video; use Balanced (23) or High (18) for anything you want to keep.
• Dropping a full hour of DV footage into the page, which hits the 1 GB limit and stops the job; split the capture into shorter parts first.
• Deleting the original AVI straight after converting, which leaves you with no clean source if a setting was wrong; keep the AVI until you have watched the MP4 all the way through.
• Converting the same clip twice to shrink it, which stacks compression loss; go back to the original AVI and pick a higher CRF value instead.
• Closing or hiding the tab during processing, which slows or kills the encode; leave the tab visible until the Download button appears.

Frequently asked questions

Is this AVI to MP4 converter free? Yes, the converter is free and needs no account. It runs in your browser, so there is no upload queue, only a 1 GB size cap per file.

Will converting AVI to MP4 lose quality? Yes, a small amount, because H.264 is a lossy codec and the video has to be re-encoded. At Balanced (23) or High (18) the difference is hard to see on typical old footage, while the file is usually much smaller than a DV or Motion JPEG source.

Are my AVI files uploaded to a server? No, the file is decoded and encoded inside your browser tab. Only the video engine itself is downloaded once; your footage stays on your device.

Why does my AVI not play in the preview but still converts? The preview uses your browser’s built-in player, which does not understand DivX, Xvid or DV. The conversion uses a separate engine that includes those decoders, so the MP4 result previews normally.

Give your old AVI files a second life

Old AVI clips do not need special software or a paid service to become usable again. Re-encoding them to H.264 MP4 makes them play on current phones, TVs and store platforms, and doing it in the browser keeps private family footage off other people’s servers. Open the AVI to MP4 Converter, start with Balanced (23), and keep the original until you have checked the result.