Free online H264 to AVI converter

Legacy video editors, surveillance systems, and older playback devices may require an AVI container instead of H.264 video in MP4, MKV, or MOV. Converting the video and, when necessary, the audio creates a file those applications can open, but it can increase size and reduce quality.

What the H264 format is

H.264, also called AVC, is a video compression standard rather than a complete container format. Cameras, smartphones, screen recorders, CCTV systems, and video editors commonly store H.264 video in .mp4, .mkv, .mov, or .ts files. A raw H.264 elementary stream may use the .h264 extension and usually contains no audio; it may also lack reliable timing information.

H.264 produces relatively small files at a given visual quality, which makes it common for recording, streaming, distribution, and archiving. The extension identifies the container, not necessarily the codec: an AVI file can contain H.264, although many older AVI applications cannot decode that combination.

What the AVI format is

AVI, or Audio Video Interleave, is a Microsoft container based on the RIFF specification. It can hold video and audio streams, but its original design predates modern streaming, variable-frame-rate timing, and many current metadata features.

AVI remains useful when older Windows software, industrial equipment, or an editing workflow explicitly requires it. For broad legacy compatibility, AVI is commonly paired with MPEG-4 Part 2, Motion JPEG, or uncompressed video rather than H.264. Motion JPEG and uncompressed AVI files can be much larger than the original H.264 file.

Convert with FFmpeg

FFmpeg is the most flexible desktop option. It accepts raw .h264 input as well as H.264 video inside MP4, MKV, MOV, and other containers. Run the command from a terminal in the folder containing the source.

ffmpeg -i input.mp4 -c:v mpeg4 -q:v 3 -c:a libmp3lame -b:a 192k output.avi

This encodes video as MPEG-4 Part 2 and audio as MP3, a combination supported by many older AVI programs. With FFmpeg's native MPEG-4 encoder, lower -q:v values generally provide higher quality and larger files; values from 2 to 5 are a practical starting range. Replace input.mp4 with the actual MP4, MKV, MOV, or TS filename.

For a raw H.264 file that has no audio, use:

ffmpeg -i input.h264 -c:v mpeg4 -q:v 3 -an output.avi

A raw elementary stream may not contain frame-rate information. If the recording rate is known, supply it so FFmpeg does not assume an incorrect timing value:

ffmpeg -r 30 -i input.h264 -c:v mpeg4 -q:v 3 -an output.avi

Replace 30 with the recording's actual frame rate. A raw .h264 file cannot regain audio that was stored separately or omitted during recording; mux the separate audio source explicitly if one exists.

If the receiving program supports H.264 in AVI and only the container must change, try stream copying:

ffmpeg -i input.mp4 -c:v copy -c:a copy output.avi

This avoids re-encoding and preserves quality, but the command can fail or produce an unusable file when the audio codec, H.264 stream, timestamps, or AVI support in the target program is incompatible. For older software, re-encoding to MPEG-4 Part 2 or Motion JPEG is usually safer.

Use a graphical converter

A desktop front end such as Avidemux can perform the same conversion without command-line options. Open the file with File → Open, select an AVI-compatible MPEG-4 Part 2 or Motion JPEG video encoder, select MP3 or another codec supported by the target application for audio, choose AVI as the output container, and save the result. Menu names and available codecs vary by version.

You can also convert the file on 101convert.com for free without installing software: upload the source, choose AVI as the output format, start the conversion, and download the generated file. Check that the service accepts the source's container and audio stream before relying on the result.

Quality and compatibility limits

Re-encoding H.264 to MPEG-4 Part 2 or Motion JPEG is lossy. The AVI file cannot restore detail already discarded by the original H.264 encoding, so keep the source and use a higher-quality setting when visual fidelity matters.

Dimensions and frame rate normally remain unchanged during conversion, but older AVI software may reject variable-frame-rate video, unusual pixel formats, high resolutions, or audio with unsupported timing. To create a constant 30 fps file with standard audio, for example, use:

ffmpeg -i input.mp4 -vf fps=30 -c:v mpeg4 -q:v 3 -c:a libmp3lame -ar 48000 -b:a 192k output.avi

AVI has limited support for chapters, multiple subtitle tracks, HDR metadata, and variable-frame-rate timing. If the target application accepts MP4 or MKV, retaining the original H.264 file or remuxing it into a modern container avoids unnecessary quality loss and usually provides better compatibility.