CONVERT OPUS → GSM (OPUS to GSM)
Fast, secure OPUS to GSM conversion. No registration required.
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HOW TO CONVERT OPUS → GSM
Give us the OPUS
Select a OPUS (or several for batch). We read the header to pick decoder settings automatically.
Re-encode to GSM
The audio is decoded, optionally resampled, and re-encoded as GSM at transparent default bitrate.
Retrieve your GSM
Grab the download as soon as it is ready. Typical jobs finish in seconds for short clips.
Here is the short version — Opus is the modern low-latency royalty-free codec used in VoIP, streaming, and WebRTC. Hence the need for GSM. Moving audio from OPUS into GSM is a routine job for podcasters, musicians, transcribers and anyone who needs a file to play somewhere the original would not. KaijuConverter reads the OPUS once, re-encodes through FFmpeg at the bitrate you choose, and returns a polished GSM in seconds. Worth knowing: Opus is the modern low-latency royalty-free codec used in VoIP, streaming, and WebRTC. Meanwhile GSM is an audio format with specific trade-offs between file size, bitrate flexibility, and device support.
Why convert OPUS to GSM
The motivation for a OPUS → GSM conversion is almost always practical: a playback device, hosting platform or editing suite that insists on GSM. The audio quality trade-off is controllable via bitrate; the compatibility win is immediate and unambiguous.
OPUS vs GSM — Technical specifications
Side-by-side comparison of the technical details.
OPUS
- MIME type
- audio/opus
- Extensions
- .opus, .ogg (container)
- Standard
- RFC 6716 (2012)
- Sample rates
- 8, 12, 16, 24, 48 kHz
- Latency
- 5-60 ms (configurable)
- MIME Type
- audio/opus
- Extension
- .opus
- Category
- Audio Files
- Full Name
- Opus Audio
- Conversion Engine
- FFMPEG
GSM
- MIME type
- audio/gsm
- MIME Type
- audio/gsm
- Extension
- .gsm
- Category
- Audio Files
- Full Name
- GSM Audio
- Conversion Engine
- FFMPEG
- Codec
- GSM 06.10 (RPE-LTP)
- Sample rate
- 8 kHz
- Bitrate
- 13 kbps
| Specification | OPUS | GSM |
|---|---|---|
| MIME type | audio/opus | audio/gsm |
| Extensions | .opus, .ogg (container) | — |
| Standard | RFC 6716 (2012) | — |
| Sample rates | 8, 12, 16, 24, 48 kHz | — |
| Latency | 5-60 ms (configurable) | — |
| MIME Type | audio/opus | audio/gsm |
| Extension | .opus | .gsm |
| Category | Audio Files | Audio Files |
| Full Name | Opus Audio | GSM Audio |
| Conversion Engine | FFMPEG | FFMPEG |
| Codec | — | GSM 06.10 (RPE-LTP) |
| Sample rate | — | 8 kHz |
| Bitrate | — | 13 kbps |
OPUS vs GSM — Strengths and limitations
What each format does best, and where it falls short.
OPUS Strengths
- Best-in-class quality across the entire bitrate range.
- Royalty-free and patent-free.
- Ultra-low latency — suitable for live voice and music.
- Handles speech and music equally well — no need to switch codecs.
- Mandatory codec in WebRTC, so supported in every browser by design.
Limitations
- Very low hardware decoder adoption — software-only on most phones.
- Older platforms (legacy Windows apps, old cars) may not play .opus files.
- Container semantics confusing — Opus lives inside Ogg, WebM, or MP4.
GSM Strengths
- Tiny bitrate (13 kbps) — hours of speech in a few MB.
- Speech-optimized — clear voice reproduction.
- Universal cellphone decoder adoption 1991-2015.
- Stable since 1987.
Limitations
- Speech-only — music sounds distorted.
- 8 kHz sampling — narrowband, muffled by modern standards.
- Legacy — LTE VoLTE moved to AMR-WB, Opus, or EVS.
Quality & Compatibility
The GSM output is as good as the OPUS source allows. If the OPUS was encoded at 96 kbps, the GSM cannot reconstruct detail the encoder already dropped; picking a very high GSM bitrate just produces a larger file. Match GSM bitrate to the OPUS quality for the best balance.
Tips for Best Results
- Sample-rate mismatches between OPUS and target device (48 kHz phone output from a 44.1 kHz track) are handled automatically; no manual resampling needed.
- For audiobook delivery, match the platform spec exactly — ACX requires 192 kbps CBR 44.1 kHz stereo, for example.
- Batch-convert an album in one job so every track shares identical encoder settings and loudness normalisation.
Frequently Asked Questions
Lossy-to-lossy conversions (most combinations) re-compress the audio, which technically introduces some loss. At a 192 kbps or higher target it is inaudible on normal equipment. Lossy-to-lossless conversions freeze the existing quality but cannot improve it; lossless-to-lossy transcodes are only as good as the target bitrate you choose.
For voice content (podcasts, audiobooks, lectures) 128 kbps is indistinguishable from higher bitrates. For music, 192-256 kbps covers most listening; 320 kbps is the ceiling for GSM and the right choice for audio you plan to edit further. Above that, prefer a lossless target instead.
Yes. Title, artist, album, year and cover art travel from the OPUS container to the GSM container automatically where both formats support them. If a tag field has no GSM equivalent, it is dropped silently. Use any tag editor (Mp3tag, MusicBrainz Picard) to fine-tune afterwards.
Opus Audio
Source formatOpus is a versatile, open-source audio codec optimized for both speech and music at very low bitrates. It is the standard for WebRTC voice calls and excels at real-time communication.
GSM Audio
Target formatGSM 06.10 is a speech compression standard designed for the Global System for Mobile Communications. It encodes speech at 13 kbps using Regular Pulse Excitation with Long Term Prediction, optimized for voice intelligibility over cellular networks.
Going the other way? Convert GSM back to OPUS with the same engine.
Common Use Cases
Share across platforms
Send GSM files to anyone without worrying about whether they have the right software for OPUS.
Embed in documents
Drop GSM output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
GSM often produces smaller files than OPUS for web, email and storage.
Archive & future-proof
Store in a widely-supported format that will still open on future operating systems without legacy plugins.
OPUS vs GSM — Typical file sizes
Approximate file sizes for common scenarios.
- Voice call (24 kbps) 180 KB/min
- Podcast (48 kbps) 21 MB/hour
- Music (128 kbps) ~1 MB/min
- 1 min of voice ~100 KB
- 1 hour voicemail archive ~6 MB
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Related comparisons
See these formats side by side to understand which fits your use case best.
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