FLAC vs SPX
A detailed comparison of FLAC Audio and Speex Audio — file size, quality, compatibility, and which format to choose for your workflow.
FLAC Audio
Audio FilesFLAC is an open-source lossless audio codec that compresses audio to roughly 50-60% of its original size without any quality loss. It is the preferred format for audiophiles and music archival.
About FLAC filesSpeex Audio
Audio FilesSpeex is an open-source audio compression format specifically designed for speech encoding. It uses Code-Excited Linear Prediction (CELP) and supports narrowband, wideband, and ultra-wideband modes for different speech quality requirements.
About SPX filesStrengths Comparison
FLAC Strengths
- Lossless — decoded audio is bit-exact identical to the source.
- 40-60% smaller than uncompressed WAV/AIFF.
- Free, patent-free, open-source reference implementation.
- Built-in error detection via MD5 checksums.
- Streaming-friendly — seek tables let you jump to any timestamp instantly.
SPX Strengths
- Patent-free voice codec.
- Three sample-rate modes for voice.
- Low CPU decode.
Limitations
FLAC Limitations
- File sizes still large compared to lossy codecs (5-10× bigger than AAC for same audio).
- Not suitable for low-bandwidth scenarios like streaming on mobile data.
- Older MP3 players and car stereos may not decode FLAC.
- Slower to encode than lossy codecs.
SPX Limitations
- Deprecated in favor of Opus.
- No music support.
- Rarely used in new projects.
Technical Specifications
| Specification | FLAC | SPX |
|---|---|---|
| MIME type | audio/flac | audio/speex |
| Extension | .flac | .spx |
| Standard | Open-source reference implementation (Xiph.Org) | — |
| Max bit depth | 32 bits per sample | — |
| Max sample rate | 655 350 Hz | — |
| Max channels | 8 | — |
| Container | — | Ogg |
| Modes | — | Narrowband/Wideband/Ultra-wideband |
| Successor | — | Opus |
Typical File Sizes
FLAC
- 3-min song (CD quality) 20-30 MB
- Full album (10 tracks, CD) 250-400 MB
- 3-min song (hi-res 24-bit/96 kHz) 80-120 MB
- Live concert recording (24-bit) 2-10 GB
SPX
- 1 min voice (wideband 24 kbps) ~180 KB
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Frequently Asked Questions
FLAC (Free Lossless Audio Codec) is an open-source audio format that compresses audio without any quality loss. Developed by the Xiph.Org Foundation, it typically reduces file sizes by 40-50% compared to WAV while preserving bit-perfect audio.
SPX (Speex Audio) is an audio file format used to store sound recordings — music, voice, podcasts, sound effects. The format defines how the audio samples are compressed (or stored raw), what bitrates are supported, and how metadata such as title, artist, album, and cover art is embedded. It is part of the audio files family.
FLAC files play in VLC, foobar2000, Winamp, and most modern music players. Streaming services like Tidal and Amazon Music HD use FLAC. Android supports it natively, and Apple devices support it via third-party apps.
VLC, foobar2000, and the default media players on Windows and macOS handle SPX natively. On mobile, iOS Music and Android media apps vary in their support — popular formats work everywhere; niche ones may need a dedicated app. If playback fails on a device, converting to MP3 or AAC usually solves it.
Both are lossless with similar compression ratios. Use FLAC for universal compatibility and open-source support. Use ALAC if you are fully invested in the Apple ecosystem since iTunes and Apple Music handle ALAC natively.
Upload the SPX to KaijuConverter and pick MP3, WAV, FLAC, AAC, OGG, or any other target. Our FFmpeg pipeline decodes the audio and re-encodes to the target format at sensible default bitrates (VBR ~190 kbps for music, 96 kbps for speech). Metadata and cover art travel with the audio where both formats support them.