Free online AVI to H264 converter

A phone, browser, smart TV, or editing application may reject an AVI file because its internal codec is unsupported. Converting it to H.264 video in an MP4 container usually improves compatibility and can reduce size for sharing, editing, or archiving.

What the AVI format is

AVI (Audio Video Interleave) is a Microsoft container format introduced in the 1990s. It can store video and audio encoded with different codecs, including DivX, Xvid, and Motion JPEG, so two .avi files can have very different quality, size, and playback requirements.

AVI remains common in older Windows software, legacy cameras and camcorders, screen-recording applications, archived footage, and older editing workflows. The container has limited support for modern streaming features, and many AVI files use codecs that are inefficient or unsupported by current phones, browsers, televisions, and editors.

What the H.264 format is

H.264, also called AVC, is a video codec rather than a container. It provides efficient lossy compression and broad support across browsers, mobile devices, televisions, game consoles, media players, and editing software.

H.264 video is usually stored in an MP4 container with the .mp4 extension, commonly alongside AAC audio. It can also be stored in containers such as MKV or MOV. Therefore, converting an AVI file to H.264 normally means decoding the AVI, re-encoding its video with H.264, and saving the result as MP4/H.264 rather than creating a standalone H.264 file.

How to convert an AVI file

You can convert the file on 101convert.com for free without installing software. Select the AVI file, choose H.264 as the video codec or MP4 as the output format when those options are available, start the conversion, and download the result. If codec information is shown, confirm that the output uses H.264 video; an .mp4 extension alone does not identify the video codec.

For private files, large inputs, batch jobs, or precise settings, use local software such as HandBrake or FFmpeg.

Using HandBrake

1. Open HandBrake and choose Open Source, then select the .avi file.
2. On the Summary tab, set the format to MP4.
3. On the Video tab, select H.264 (x264) as the video encoder.
4. Set Constant Quality to about RF 20–23 as a starting point. Lower RF values increase quality and file size; higher values increase compression and reduce quality.
5. Keep the source dimensions and frame rate unless the destination device requires different values. Select AAC audio when broad MP4 compatibility matters.
6. Choose a destination ending in .mp4 and click Start Encode.

Using FFmpeg

FFmpeg provides command-line control and supports automation. This command creates an MP4 file with H.264 video and AAC audio:

ffmpeg -i input.avi -c:v libx264 -crf 23 -preset medium -c:a aac -b:a 160k -movflags +faststart output.mp4

-crf 18–20 generally preserves more quality with larger files, while -crf 26–28 creates smaller files with more visible compression. Use -preset slow for better compression at the cost of encoding time, or -preset fast for a quicker encode at a usually larger size. The -movflags +faststart option moves MP4 metadata to the beginning for faster playback while downloading in compatible players.

You can copy the audio without re-encoding by replacing the audio options with -c:a copy, but only if the source audio codec is supported by MP4 and the target devices. AAC is the safer choice when the AVI contains an unusual audio codec.

Quality and compatibility caveats

• Re-encoding is normally lossy. H.264 cannot restore detail already lost in the AVI, and converting a compressed AVI may introduce another generation of loss. Use a lower CRF or RF value when quality matters.
• H.264 compression does not guarantee a smaller file. Size depends on the source codec, resolution, frame rate, motion, quality setting, and audio.
• Interlaced AVI footage may show comb-shaped edges during motion. Enable deinterlacing when the source is interlaced, especially for progressive phone, web, and computer playback.
• Very old AVI files may use obsolete codecs that current software cannot decode. FFmpeg or HandBrake may need an additional compatible decoder, and a damaged file may fail in every converter.
• Subtitles, chapters, metadata, multiple audio tracks, and unusual AVI features may not transfer exactly. Check the output before deleting the source.
• MP4/H.264 with AAC is generally more compatible than a raw .h264 elementary stream. A raw stream has no normal container for audio, timing, subtitles, or metadata and is mainly useful when a specific production or hardware system requires it.