Free online AVC to WEBM converter

A browser, web application, or video platform may require WebM instead of an H.264/AVC file, especially for HTML5 playback and smaller web-delivery files. Converting requires re-encoding the video because WebM does not normally contain AVC video.

What the AVC format is

AVC usually refers to H.264/MPEG-4 AVC, a video codec used in MP4, MOV, MKV, MTS, TS, and some files with the .avc extension. Cameras, screen recorders, video editors, Blu-ray workflows, streaming systems, and phones commonly create AVC video.

A file named .avc may contain a raw H.264 elementary stream rather than a standard container. Raw AVC files often have no reliable duration, audio track, or metadata, so conversion software may need the codec specified explicitly.

What the WEBM format is

WebM is a Matroska-based container designed for web playback. It commonly contains VP8, VP9, or AV1 video and Vorbis or Opus audio; VP9 with Opus is a practical default for broad modern-browser support.

WebM is useful for HTML5 video, browser-based applications, and web delivery. It can produce smaller files than AVC at comparable quality when using VP9 or AV1, but encoding is usually slower. WebM is not supported equally by older browsers, editing applications, televisions, or hardware players.

How to actually convert AVC to WEBM

Using FFmpeg

Install FFmpeg, then use a command appropriate to the source container:

ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 32 -b:v 0 -c:a libopus -b:a 128k output.webm

Here, -crf 32 controls VP9 quality; lower values improve quality and increase file size. Values around 28–35 are common starting points. -b:v 0 enables constrained-quality mode, while -c:a libopus -b:a 128k encodes stereo audio at 128 kbps.

For a raw H.264 file with no container, specify the input format:

ffmpeg -f h264 -i input.avc -c:v libvpx-vp9 -crf 32 -b:v 0 -an output.webm

Use -an only when the source has no audio. If a separate audio file exists, combine it during conversion:

ffmpeg -f h264 -i video.avc -i audio.wav -c:v libvpx-vp9 -crf 32 -b:v 0 -c:a libopus -b:a 128k -shortest output.webm

For a smaller, faster encode, use VP8:

ffmpeg -i input.mp4 -c:v libvpx -crf 10 -b:v 1M -c:a libvorbis -q:a 5 output.webm

Replace input.mp4 or input.avc with the actual filename. FFmpeg can read many AVC-containing containers without the -f h264 option; use that option only for a raw elementary stream.

Using the online converter

You can convert the file for free on 101convert.com without installing software: open the AVC-to-WEBM converter, choose the source file, start the conversion, and download the resulting .webm file. Upload limits, processing time, and supported source types depend on the service.

Quality, compatibility, and limitations

Because AVC and WebM use different video codecs, ordinary conversion is a lossy re-encode. Avoid repeated conversions, and keep the original AVC file as a master. Inspect the result for synchronization, subtitles, variable frame-rate behavior, and lost metadata.

Use VP9 for general browser compatibility and good compression. Use AV1 only when the playback environment supports it and longer encoding time is acceptable. For maximum compatibility with older devices, AVC in MP4 may remain a better distribution format than WebM.

Raw .avc input may lack frame-rate information. If playback speed is wrong, provide the source frame rate explicitly, for example:

ffmpeg -f h264 -framerate 30 -i input.avc -c:v libvpx-vp9 -crf 32 -b:v 0 -an output.webm

Set -framerate to the rate used when the source was recorded; guessing can produce incorrect duration or audio synchronization.