Difference between revisions of "Helix MP3 Encoder"
From Hydrogenaudio Knowledgebase
Maikmerten (Talk | contribs) (some initial encoder switch documentation) |
Maikmerten (Talk | contribs) (add some MP3 listening tests with Helix) |
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* LAME headers for gapless playback | * LAME headers for gapless playback | ||
* CBR and VBR encoding | * CBR and VBR encoding | ||
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| + | == Listening tests == | ||
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| + | The Helix MP3 encoder participated in several listening tests and demonstrated to be amongst the highest-quality encoders for MP3 available. | ||
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| + | * [https://listening-tests.hydrogenaud.io/sebastian/mp3-128-1/results.htm Public MP3 listening test, October 2008] | ||
| + | * [https://hydrogenaud.io/index.php/topic,100896.0.html Personal listening test by Kamedo2, ~224 kbps, May 2013] | ||
| + | * [https://hydrogenaud.io/index.php/topic,113324.0.html Personal listening test by Kamedo2, ~192 kbps, December 2016] | ||
Revision as of 11:22, 25 March 2024
The Helix MP3 Encoder was open-sourced by RealNetworks ca. 2005 via the (long-defunct) Helix community project. It originated from the Xing MP3 encoder, which was purchased by RealNetworks.
A current version ("hmp3"), with contributions from HydrogenAudio members, is available as source code over at https://github.com/maikmerten/hmp3. This Wiki page discusses that version.
Features
- Supports MPEG-1 and MPEG-2 modes
- 48 kHz, 44.1 kHz, 32 kHz (MPEG-1)
- 24 kHz, 22.05 kHz, 16 kHz (MPEG-2)
- LAME headers for gapless playback
- CBR and VBR encoding
Listening tests
The Helix MP3 encoder participated in several listening tests and demonstrated to be amongst the highest-quality encoders for MP3 available.
- Public MP3 listening test, October 2008
- Personal listening test by Kamedo2, ~224 kbps, May 2013
- Personal listening test by Kamedo2, ~192 kbps, December 2016
Encoder switches
hmp3 is a command-line operated application. The most basic invocation to generate a MP3 file from WAV:
hmp3 input.wav output.mp3
This creates a ~128 kbps VBR file for 44.1 kHz stereo input.
| Switch | Function | Example |
|---|---|---|
| -B | Set per-channel bitrate. Selects CBR encoding. | -B64 for a 128 kbps stereo CBR file |
| -F | Frequency cutoff for the encoder lowpass filter. To actually encode anything beyond 16 kHz, also specify the -HF switch. | -F19000 for a 19 kHz lowpass |
| -HF | Controls encoding of high frequency content (> 16 kHz). Disabled by default. Valid values are 0 (disabled), 1 (partial, only "mode-1 granules"), 2 (full, "all granules"). Note that high-frequency content will only be encoded if the psychoacoustic model deems encoding high frequencies as beneficial for the given bitrate/quality settings. | -HF2 for unrestricted high-frequency encoding |
| -SBT | Threshold for short-block decisions. Lower values mean more short-block usage. Default is 700. | -SBT500 for more short-blocks (more responsive to transients, might increase bitrate in VBR) |
| -V | Quality setting for VBR encoding. Ranges from 0 to 150. Default is 50. | -V115 for a ~180-200 kbps stereo VBR file |
