How to detect MP3 Stereo eXtended / Surround ?


Is there any Mp3tag systemvar that can display if a mp3 file has been coded as 'MP3 Mono', 'MP3 Stereo', 'MP3 eXtended', 'MP3 Surround' and so on?



Only %_mode% which returns Stereo, Joint Stereo and Mono if I am not mistaken.


Is there a chance to have %_mode% returning 'MP3 eXtended', 'MP3 Surround' too?



Don't think so. I just downloaded a test file and the MP3 frames are marked as Joint Stereo. I guess the surround information is stored somewhere else like SBR data is stored in mp3PRO.


... hmm, the Fraunhofer IIS MP3 Surround Decoder WinAmp Plugin displays the different coding modes.
Maybe there are sources on the internet that describe how to detect those special modes, number of channels and something else.
I would like to see those mode ability in Mp3tag as soon as possible.


I do not know if surround mode is directly coded in the MP3 header bitfields but the quote above sounds to me that there is an 'ancillary data field of the MP3 bitstream' that might be evaluated.



Yep, as I thought - the surround information is stored in more or less the same way as the SBR information is stored in mp3PRO. However, I doubt Florian has any plans to implement support for these MP3s because they are not really wide spread - people who need more audio channels usually encode to Ogg Vorbis or AAC/MP4.

Edit: Oh, by the way - you are right that the Winamp input plugin recognizes the files, but since it's a decoder, it has to parse the ancillary data, while Mp3tag relies on the frame headers which are much easier to spot and decode.