Having a .mp3 message file format to add a new system recording, what format should I choose (or you choose) for conversion among the nine available at page end , and why, to achieve best quality ?
I think WAV is probably the most universal.
That all depends on what you want to do. wav will be the default format but that always requires transcoding. When Asterisk is looking to playback a file it always looks for the format that matches the codec being used on the channel. So if you’re using g711u, it will look for a .ulaw version of the recording. If you’re doing g722, it will look for .g722 format of the file.
I always used WAV and sure, transcoding uses resources, but how about quality ?
The original high quality mp3 file is converted in less-quality format , but is the converted quality the same despite wav, g711,sln etc ?
Asterisk .wav has the same quality as Asterisk.sln, but has a few extra bytes, as it has metadata, whereas .sln is pure payload.
Asterisk .WAV has a much lower quality than any of them (it is GSM standard rate in a wav wrapper). It’s a vocoder based format, so not suitable for music or pure tones (e.g inband DTMF)
.sln16 is higher quality than .sln, as it is sampled at 16kHz, not 8kHz.
Asterisk alaw (G.711 A-Law) and ulaw (G.711 µ-Law) have similar qualities, which are lower than .sln, but match that of the traditional PSTN.
The .sln* ones are the highest quality ones for their sampling rates. .sln48, and higher, will exceed MP3 quaility.
Thank you