Audio and video formats: quality, size and compatibility

WAV stores every sound sample uncompressed: one minute of CD-quality stereo (44.1 kHz, 16-bit) takes about 10 MB. FLAC compresses those same samples the way ZIP compresses text: playback recovers the exact signal, in a file 40% to 60% the size of the WAV. MP3, AAC, OGG Vorbis and OPUS discard detail the ear notices less to take up far less space; that loss can't be undone.

• Going from MP3 to WAV or FLAC doesn't improve the sound: it just stores what survived the MP3 without compression, in a bigger file.
• Going from one lossy format to another (AAC or OPUS to MP3) adds a second loss; whenever you can, convert from the lossless original.
• Raising an MP3's bitrate from 128 to 320 kbps doesn't recover quality: it only increases the size.

Convert WAV to FLAC without losing quality

Convert MP3 to WAV

QuickToolio's audio tools encode MP3 with LAME. If you don't choose a bitrate they use its level-2 variable quality (VBR), which gives more data to complex passages; you can also set a constant bitrate of 64, 96, 128, 160, 192, 256 or 320 kbps.

• Speech, podcasts and voice notes: 64 to 96 kbps is usually enough.
• Music for listening on a phone: 128 kbps is a good balance.
• Music where quality matters: 192 to 256 kbps, hard to tell from the original for most listeners.
• 320 kbps only makes sense if you start from a lossless original.

Change an audio file's bitrate

Reduce an MP3's size

AAC (inside M4A files) sounds slightly better than MP3 at the same bitrate and is the default for iPhone voice memos. OPUS was designed for real-time speech and sounds clear with very little data, which is why WhatsApp, Telegram and Discord use it. OGG Vorbis is patent-free and common in video games. The problem with all three is compatibility with car stereos and older software: there, MP3 is still the safe choice.

Convert M4A to MP3

Convert OPUS to MP3

Convert OGG to MP3

MP4, MOV, MKV and WEBM are containers: boxes that hold one or more video, audio and subtitle tracks. Whether a device can play the video depends on the codec of those tracks. iPhones record MOV (often with HEVC), browser screen recordings are usually WEBM (VP8, VP9 or AV1 with Opus audio), and downloaded films often come as MKV with several tracks.

When converting to MP4, QuickToolio re-encodes the video to H.264 and the audio to AAC (128 kbps), the combination practically every phone, TV and social network plays. It's a slow process because every frame is recalculated; from an MKV, only the first video and first audio track are kept, with no subtitles.

Convert MOV to MP4

Convert MKV to MP4

Convert WEBM to MP4

H.264 doesn't work towards a target size but a constant rate factor (CRF): the higher it is, the more compression. The video compressor offers three profiles, CRF 19 (high quality), 23 (balanced) and 28 (small file), and can lower the resolution to 2160, 1440, 1080, 720, 480 or 360 pixels tall, but never raises it. Because CRF measures quality, the final size depends on the content: a video with lots of motion takes more space than a static one of the same length.

• For sharing over messaging apps: balanced at 720p usually shrinks it a lot without being noticeable on a phone.
• For keeping a memory: high quality at the original resolution.
• If only the audio is unwanted, removing the audio track copies the video without re-encoding: fast and lossless.

Compress a video

Remove the audio from a video

A GIF stores every frame as an image with at most 256 colours and without a video's inter-frame compression, so a few seconds of GIF can take more space than a minute of MP4. That's why the MP4 to GIF conversion uses only the first 30 seconds and first computes a colour palette specific to the video, to reduce banding.

Convert an MP4 video to GIF

The first conversion downloads the FFmpeg engine (about 7 MB), which runs on a single WebAssembly thread inside your browser: the file never leaves your device, but a long video can take several minutes to re-encode on a modest laptop. Each file can be up to 300 MB; extracting the audio from a video is much faster than converting the whole video.

Extract the audio from an MP4 as MP3