Free online 264 to ASF converter

What the 264 format is

.264 usually identifies a raw H.264/AVC elementary video stream, not a complete container format. It contains compressed video bitstreams but normally has no audio track, filename metadata, reliable timestamps, or standard frame-rate declaration.

Security cameras, DVRs, video encoders, FFmpeg, and some editing or capture applications create these files. Camera-generated files can also use the extension for a proprietary stream that only resembles standard H.264; such files may fail in general-purpose converters even when their names end in .264.

What the ASF format is

ASF, or Advanced Systems Format, is a Microsoft container designed for streaming and storing synchronized audio and video. The usual extension is .asf; Windows Media Video files commonly use the related .wmv extension.

ASF stores timestamps, stream information, metadata, and error-resilience data that a raw H.264 stream lacks. It is useful when a legacy Windows application, media server, or device specifically requires ASF. Compatibility is generally better with Windows Media codecs such as WMV2 than with H.264 carried inside ASF.

How to convert 264 to ASF

Using 101convert.com

1. Open the video converter on 101convert.com; it can be used free without installing software.
2. Upload the .264 file and select ASF or .asf as the output format.
3. If the converter asks for a frame rate, enter the rate used by the camera or encoder, such as 25 or 30 fps.
4. Start the conversion, download the resulting .asf file, and test it in the target application.

Do not upload sensitive surveillance footage unless the service's file-handling and retention terms meet your requirements.

Using FFmpeg on a desktop

FFmpeg is suitable when the source is a standard raw H.264 stream. First identify the recording frame rate; raw .264 files commonly do not contain it. Then run:

ffmpeg -f h264 -framerate 25 -i input.264 -c:v wmv2 -b:v 2M -pix_fmt yuv420p -an output.asf

Replace 25 with the actual source rate and adjust 2M to the required video bitrate. The command encodes the video as WMV2, which is usually more compatible with ASF readers. Because the source is normally video-only, -an prevents FFmpeg from expecting an audio stream.

If the target software accepts H.264 in ASF, you can try remuxing without re-encoding:

ffmpeg -f h264 -framerate 25 -i input.264 -c:v copy -an output.asf

This preserves the original video quality, but the ASF muxer or playback device may reject H.264, and the missing source timestamps can produce incorrect duration or seeking. Use the WMV2 command when broad legacy compatibility matters more than avoiding a second encode.

Quality, compatibility, and limitations

• Transcoding from H.264 to WMV2 is lossy. Increasing the bitrate reduces additional quality loss but does not restore detail already lost in the source.
• A raw .264 file generally has no audio. Converting it to ASF does not create audio; an audio track must be supplied separately and synchronized before muxing.
• If playback speed is wrong, the input frame rate is probably incorrect. Reconvert using the camera's actual rate rather than relying on FFmpeg's default assumptions.
• Some DVR files contain proprietary headers, encryption, interleaved audio, or multiple camera streams. FFmpeg may report invalid NAL units or produce a short, silent output; the manufacturer's export utility may be required first.
• Check the output with the exact application or device that requires ASF. ASF support varies, and some readers accept only particular Windows Media codecs, resolutions, or bitrate ranges.