Free online FLV to AAC converter

Older FLV downloads and archived Flash media may contain audio needed by an editor, player, or device that accepts AAC but cannot use FLV. Removing the video stream also creates a smaller audio-only file.

What FLV is

FLV (Flash Video) is a multimedia container created for Adobe Flash web streaming and playback. Older websites, Flash-based players, screen-recording software, and downloaded web videos used it; current browsers no longer support Flash.

An FLV file can contain video such as H.264, VP6, or Sorenson Spark and audio such as AAC, MP3, Nellymoser, or Speex. The audio codec inside the container determines whether the sound can be copied directly or must be re-encoded.

What AAC is

AAC (Advanced Audio Coding) is a lossy audio codec used in MP4 and M4A files, mobile devices, streaming services, and many media players. AAC generally delivers better audio quality than MP3 at similar bitrates, particularly at lower bitrates.

A filename ending in .aac normally contains an AAC elementary stream with ADTS headers. Use this format only when the receiving program specifically requests AAC; use .m4a when the player expects an MP4-based audio file or needs standard support for artwork and metadata.

Convert the file

Upload the FLV file to the converter on 101convert.com, choose AAC as the output format, start conversion, and download the resulting .aac file. The service removes the video stream and encodes the selected audio stream as AAC when required.

For local conversion, FFmpeg provides explicit stream selection and bitrate control:

ffmpeg -i input.flv -map 0:a:0 -vn -c:a aac -b:a 192k output.aac

-map 0:a:0 selects the first audio stream, -vn excludes video, and -b:a 192k sets the AAC bitrate. A bitrate around 128k is often sufficient for speech; 192k is a common choice for music. Inspect a file with ffprobe input.flv if it has multiple audio tracks.

If the FLV already contains AAC audio, copy it instead of encoding a second lossy version:

ffmpeg -i input.flv -map 0:a:0 -vn -c:a copy output.aac

Confirm the source codec first:

ffprobe -v error -select_streams a:0 -show_entries stream=codec_name -of default=nw=1 input.flv

Quality and compatibility limits

Converting MP3, Speex, Nellymoser, or low-bitrate AAC to AAC cannot improve the original sound. Re-encoding lossy audio adds another generation of loss, so retain the original when possible and avoid choosing a bitrate merely to make a poor source sound better.

Stream copying works only for AAC audio. A copied .aac file may still be rejected by software that expects AAC inside an M4A container; in that case, create M4A instead:

ffmpeg -i input.flv -map 0:a:0 -vn -c:a aac -b:a 192k output.m4a

If the FLV source is already AAC and the destination accepts M4A, replace -c:a aac -b:a 192k with -c:a copy to avoid re-encoding.