ffmpeg-audio-extraction

name	ffmpeg-audio-extraction
description	Extracts audio tracks from video files using ffmpeg with optimal settings. Supports format conversion, resampling, and channel mixing. Use when extracting audio from video, converting audio formats, preparing audio for speech recognition, or processing media files.
compatibility	Requires ffmpeg command-line tool
metadata	{"author":"video2doc","version":"1.0"}

FFmpeg Audio Extraction

Extract and convert audio from video files using ffmpeg.

When to Use

• Extracting audio track from video files
• Converting audio to specific format/sample rate
• Preparing audio for speech recognition (Whisper)
• Processing media files for further analysis

Prerequisites

Verify ffmpeg installation:

ffmpeg -version

Tip: Getting FFmpeg

• macOS: brew install ffmpeg
• Linux: apt install ffmpeg or dnf install ffmpeg
• Windows: Download from BtbN/FFmpeg-Builds, e.g. ffmpeg-n7.1-latest-win64-gpl-shared-7.1.zip, extract and add bin/ to PATH

Alternatively, set FFMPEG_PATH environment variable to the ffmpeg executable path.

Common Operations

Extract Audio (Keep Original Format)

ffmpeg -i video.mp4 -vn -acodec copy audio.aac

Parameters:

• -vn - No video
• -acodec copy - Copy audio without re-encoding

Extract for Whisper (Recommended)

Whisper expects 16kHz mono audio:

ffmpeg -i video.mp4 -vn -acodec pcm_s16le -ar 16000 -ac 1 audio.wav

Parameters:

• -acodec pcm_s16le - 16-bit PCM (uncompressed)
• -ar 16000 - 16kHz sample rate
• -ac 1 - Mono channel

Extract to MP3

ffmpeg -i video.mp4 -vn -acodec libmp3lame -q:a 2 audio.mp3

Parameters:

• -q:a 2 - Quality level (0-9, lower is better)

Extract to FLAC (Lossless)

ffmpeg -i video.mp4 -vn -acodec flac audio.flac

Python Integration

import subprocess
from pathlib import Path

def extract_audio(
    video_path: Path,
    audio_path: Path,
    sample_rate: int = 16000,
    mono: bool = True,
) -> bool:
    """Extract audio from video using ffmpeg."""
    cmd = [
        "ffmpeg",
        "-i", str(video_path),
        "-vn",                      # No video
        "-acodec", "pcm_s16le",     # 16-bit PCM
        "-ar", str(sample_rate),    # Sample rate
        "-ac", "1" if mono else "2", # Channels
        "-y",                       # Overwrite
        str(audio_path),
    ]
    
    result = subprocess.run(
        cmd,
        capture_output=True,
        text=True,
    )
    
    return result.returncode == 0

Get Media Information

Duration

ffprobe -v quiet -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 video.mp4

Full Metadata (JSON)

ffprobe -v quiet -print_format json -show_format -show_streams video.mp4

Python Helper

import subprocess
import json

def get_video_info(video_path: str) -> dict:
    """Get video metadata using ffprobe."""
    cmd = [
        "ffprobe",
        "-v", "quiet",
        "-print_format", "json",
        "-show_format",
        "-show_streams",
        video_path,
    ]
    
    result = subprocess.run(cmd, capture_output=True, text=True)
    return json.loads(result.stdout)

def get_duration(video_path: str) -> float:
    """Get video duration in seconds."""
    info = get_video_info(video_path)
    return float(info["format"]["duration"])

Batch Processing

PowerShell - All Videos in Directory

Get-ChildItem *.mp4 | ForEach-Object {
    $output = $_.BaseName + ".wav"
    ffmpeg -i $_.FullName -vn -ar 16000 -ac 1 $output
}

Python Batch

from pathlib import Path
import subprocess

def batch_extract(input_dir: Path, output_dir: Path):
    """Extract audio from all videos in directory."""
    output_dir.mkdir(exist_ok=True)
    
    for video in input_dir.glob("*.mp4"):
        audio = output_dir / f"{video.stem}.wav"
        subprocess.run([
            "ffmpeg", "-i", str(video),
            "-vn", "-ar", "16000", "-ac", "1",
            "-y", str(audio)
        ])

Audio Quality Settings

Sample Rates

Rate	Use Case
8000	Telephone quality
16000	Speech recognition (Whisper)
22050	Low-quality music
44100	CD quality
48000	Professional audio

Bit Depth

Format	Bits	Use Case
pcm_s16le	16	Standard, Whisper compatible
pcm_s24le	24	High quality
pcm_f32le	32	Maximum precision

Troubleshooting

No Audio Stream

Stream map '0:a' matches no streams

Video may not have audio. Check with:

ffprobe -v error -select_streams a -show_entries stream=codec_type video.mp4

Encoding Errors

If specific codec fails, try:

ffmpeg -i video.mp4 -vn -acodec aac audio.m4a

Long Videos

For very long videos, consider streaming to temp file:

import tempfile

with tempfile.NamedTemporaryFile(suffix=".wav", delete=False) as f:
    audio_path = f.name
    extract_audio(video_path, Path(audio_path))

Advanced: Extract Specific Time Range

# Extract 30 seconds starting at 1:00
ffmpeg -i video.mp4 -ss 00:01:00 -t 30 -vn -ar 16000 -ac 1 clip.wav

Advanced: Multiple Audio Tracks

List tracks:

ffprobe -v error -select_streams a -show_entries stream=index,codec_name video.mkv

Extract specific track:

ffmpeg -i video.mkv -map 0:a:1 -vn audio_track2.wav