無料動画→音声変換 — 動画からMP3を抽出 | WebConverter

Need to extract the audio track from a video? Whether you want to save the soundtrack from an MP4, rip the dialogue from a screen recording, or convert a video podcast into an MP3 you can listen to on the go, WebConverter's free video-to-audio converter makes it effortless — and it all happens right in your browser. No files are uploaded, no software to install, no account needed.

This guide covers everything you need to know about extracting audio from video: which output format to choose, how bitrate affects quality and file size, step-by-step instructions, and answers to the most common questions. Whether you are a content creator, student, musician, or just someone who wants an MP3 from a video file, this page has you covered.

Why Extract Audio from Video?

There are countless reasons to pull audio out of a video file. Here are the most common scenarios:

• Create portable audio: Turn a lecture recording, conference talk, or tutorial video into an MP3 you can listen to while commuting, exercising, or doing chores.
• Podcast production: Extract the audio track from a video podcast to distribute on audio-only platforms like Spotify, Apple Podcasts, and Google Podcasts.
• Music production: Extract audio from music videos or live performance recordings for sampling, remixing, or personal use.
• Transcription preparation: Extract audio from meeting recordings or interviews before sending to a transcription service or tool.
• Save storage space: Audio files are dramatically smaller than video files. A one-hour MP4 video at 1080p might be 2–5 GB, while the extracted MP3 is just 60–100 MB.
• Sound design: Pull sound effects, ambient audio, or dialogue from video footage for use in other projects.
• Accessibility: Create audio versions of video content for people who prefer or need audio-only access.

Output Format Comparison

When extracting audio from video, you need to choose an output format. WebConverter offers four options, each with different strengths. The table below will help you pick the right one.

Quick recommendations

• For most people: Use MP3. It is the universal standard — plays everywhere, small files, good quality.
• For better quality at the same size: Use OGG. Audibly better than MP3 at equivalent bitrates.
• For editing and production: Use WAV. Uncompressed, lossless, no quality compromise.
• For lossless archival: Use FLAC. Same quality as WAV, half the file size.

Bitrate Guide: Finding the Sweet Spot

For lossy formats (MP3 and OGG), bitrate is the single most important quality setting. Higher bitrate means better audio quality but larger files. Here is a practical guide to choosing the right bitrate:

Rule of thumb: For music, use 192 kbps or higher. For speech and podcasts, 128 kbps is more than enough. If you are unsure, 192 kbps is a great default that balances quality and file size.

Note that for OGG Vorbis, you get slightly better quality than MP3 at the same bitrate, so you can often use a lower bitrate (e.g., 160 kbps OGG instead of 192 kbps MP3) and still get equivalent quality.

How to Extract Audio from Video — Step by Step

The process is quick and straightforward. Here is exactly how to do it:

1. Choose your output format. Decide which audio format you want. For most people, MP3 is the best choice. Visit the converter page for your chosen format.
2. Drop your video file. Drag and drop your video file (MP4, WebM, M4A, MOV, or any browser-supported format) onto the upload area. Alternatively, click the area to open a file browser.
3. Select your bitrate. For MP3 and OGG, choose a bitrate from the dropdown menu. The default (128 kbps) is fine for speech; choose 192 kbps or higher for music.
4. Wait for conversion. The converter decodes the audio from your video using your browser's built-in media decoder, then re-encodes it into your chosen format using a WebAssembly encoder. This typically takes a few seconds, even for long videos.
5. Download your audio file. Click the download button to save the converted audio file to your computer or phone.

That is it — five steps, no uploads, no installs, no waiting for a server to process your file. Everything happens locally on your device.

Supported Input Formats

WebConverter can extract audio from any video or audio format that your browser can decode. This typically includes:

• Video formats: MP4, WebM, MOV, M4V, OGV
• Audio formats: MP3, WAV, OGG, FLAC, M4A, WebM (audio-only), AAC

The exact list depends on your browser and operating system. Chrome, Firefox, Edge, and Safari all support MP4 and WebM. Some browsers support additional formats through the operating system's media framework. If your file does not play in the browser natively, the converter cannot decode it — but this covers the vast majority of video files people work with.

Video to MP3 — The Most Popular Conversion

By far the most common video-to-audio conversion is video to MP3. MP3 is the universal audio format — supported by every device, every music player, every car stereo, and every operating system. When people say "I want the audio from this video," they almost always mean "I want an MP3."

WebConverter's Video to MP3 converter uses a high-quality LAME encoder compiled to WebAssembly. The encoding quality is identical to what you would get from the desktop LAME encoder — the gold standard for MP3 encoding. You can choose from standard bitrates (128, 192, 256, 320 kbps) and get a perfectly encoded MP3 in seconds.

Common video-to-MP3 use cases

• Save lectures and tutorials for offline listening
• Extract music from concert videos or music videos
• Create podcast episodes from video recordings
• Pull audio from screen recordings for voiceover reuse
• Convert video messages to audio for faster consumption

Read our detailed guide: How to Convert Video to MP3 in the Browser.

Video to WAV — For Editing and Production

If you plan to edit the extracted audio — in Audacity, Adobe Audition, Logic Pro, GarageBand, or any other audio editor — you should extract it as WAV. WAV is uncompressed, so you get the full audio quality without any compression artefacts. This gives you the cleanest possible starting point for editing, mixing, and mastering.

WAV files are large (about 10 MB per minute for CD-quality stereo), but that is rarely a problem for editing workflows. You can always convert the edited result to MP3 or FLAC afterward for distribution.

Video to FLAC — Lossless Archival

If you want perfect audio quality but do not need the enormous file sizes of WAV, FLAC is the ideal choice. FLAC uses lossless compression to reduce file sizes by 40–50% compared to WAV while preserving every single sample of audio data. This makes FLAC perfect for archiving audio extracted from videos — you get bit-perfect quality in a reasonable file size, and you can always convert to MP3 or OGG later without generational quality loss.

Video to OGG — The Open-Source Choice

If you are working on a game, web application, or open-source project, OGG Vorbis is an excellent choice. It delivers better audio quality than MP3 at equivalent bitrates, and it is completely royalty-free and open-source. OGG is natively supported by Unity, Unreal Engine, Godot, and most web browsers, making it the de facto standard for game audio and web applications.

How WebConverter Handles Video-to-Audio Conversion

Understanding what happens behind the scenes can help you trust the process and troubleshoot any issues:

1. Decoding: When you drop a video file, WebConverter uses your browser's built-in AudioContext.decodeAudioData() method to decode the audio track. This is the same high-performance decoder your browser uses to play videos normally.
2. Processing: The decoded audio is represented as raw PCM samples in memory — completely uncompressed, full-quality audio data. This happens on the main thread.
3. Encoding: The PCM audio is sent to a Web Worker, which encodes it into your chosen output format. For MP3 and OGG, WebConverter uses wasm-media-encoders — the LAME MP3 encoder and libvorbis OGG encoder compiled to WebAssembly. For WAV, a pure JavaScript encoder writes the RIFF header and interleaved PCM samples. For FLAC, the native AudioEncoder API is used where available (Chrome 107+), with a WAV fallback for other browsers.
4. Download: The encoded audio file is presented as a downloadable blob — a file that exists only in your browser's memory until you save it.

At no point does any data leave your device. The entire pipeline — decode, process, encode, download — runs locally in your browser.

Privacy and Security

Traditional video-to-MP3 websites upload your video file to a remote server, process it, and send back the audio. This approach has serious problems:

• Privacy: Your video is on someone else's server. If it contains private content — a personal video call, a confidential meeting recording, a family moment — it is now in a stranger's hands.
• Speed: Uploading a large video file over the internet takes minutes. The server processing adds more time. Then you have to download the result.
• Limits: Most server-based converters restrict file sizes (often to 100 MB or less), impose daily limits, or require paid subscriptions for larger files.
• Security: There is no guarantee that the server deletes your file after processing. Data breaches at file conversion services have exposed private user files.

WebConverter is fundamentally different. Your files never leave your device. There is no upload, no server, no cloud processing. The conversion engine runs entirely in your browser using WebAssembly and the Web Audio API. You can even disconnect from the internet after the page loads and still convert files.

This makes WebConverter safe for:

• Confidential meeting recordings
• Private video messages
• Legal depositions and court recordings
• Medical dictation and consultations
• Corporate training videos
• Any video containing sensitive or personal content

Learn more: The Privacy Risk of Online File Converters.

Tips for Best Results

Here are some practical tips to get the best audio when extracting from video:

• Start with the highest quality source. The output audio can never be better than the source video's audio track. If possible, use the original, uncompressed video file rather than a compressed or re-encoded copy.
• Choose the right bitrate. Do not use 320 kbps for a podcast that was recorded at 64 kbps — it just wastes space. Match your bitrate to the quality of the source material.
• Use WAV or FLAC if you plan to edit. Never edit lossy audio (MP3/OGG) directly — each save/re-encode degrades quality. Extract as WAV, edit, then encode to your final format.
• For podcasts, 128 kbps MP3 is fine. Human speech does not benefit much from higher bitrates. Save bandwidth and storage with 128 kbps.
• For music, use 192 kbps or higher. Music has more frequency complexity than speech and benefits from higher bitrates. 192 kbps is the sweet spot for most listeners.

All Video-to-Audio Converter Tools

Jump directly to the converter you need:

• Video to MP3 — universal format, plays everywhere, smallest files
• Video to OGG — better quality than MP3, open-source, great for games
• Video to WAV — uncompressed, lossless, perfect for editing
• Video to FLAC — lossless compression, ideal for archival

For a broader overview of audio conversion, visit the Audio Converter hub page. For a deep-dive format comparison, read MP3 vs OGG vs WAV vs FLAC.

Frequently Asked Questions

Is the video-to-audio converter free?

Yes, 100% free. There are no charges, no subscription tiers, no watermarks, and no file-size limits. You can convert as many videos as you want.

Are my video files uploaded to a server?

No. WebConverter processes everything locally in your browser. Your video file never leaves your device. The conversion uses the Web Audio API for decoding and WebAssembly for encoding — all running on your own computer or phone.

What video formats can I extract audio from?

You can extract audio from any format your browser supports, which typically includes MP4, WebM, MOV, M4A, M4V, and OGV. Chrome, Firefox, Edge, and Safari all support MP4 and WebM. The exact list depends on your browser and operating system.

What is the best format for extracting audio from video?

For most people, MP3 is the best choice — it is universally compatible and produces small files. For higher quality at the same file size, use OGG. For editing or production work, use WAV (uncompressed). For lossless archival, use FLAC.

What bitrate should I use?

For speech (podcasts, lectures, audiobooks), 128 kbps is sufficient. For music, use 192 kbps or higher. If you want the absolute best MP3 quality and file size does not matter, use 320 kbps. For OGG Vorbis, you can use slightly lower bitrates for equivalent quality.

Can I extract audio from a YouTube video?

WebConverter does not download videos from YouTube or any other website. You must have the video file on your device. If you have a locally saved video, drag and drop it onto the converter to extract the audio.

How long does conversion take?

Conversion is fast — typically a few seconds for a standard-length video. Long videos (1+ hours) may take 10–30 seconds depending on your device's processing power. Because everything runs locally, there is no upload/download delay.

Does it work on mobile phones?

Yes. WebConverter works in any modern mobile browser, including Chrome and Safari on Android and iOS. You can use the file picker to select video files from your device. The interface adapts to smaller screens for comfortable use on phones and tablets.