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mpeg1 layer 2 audio (mp2 or m2a) files
28-07-2017, 12:07
Post: #1
mpeg1 layer 2 audio (mp2 or m2a) files
I have a fair number of these files from off-air radio recordings. (From a Psion Wavefinder via DAB, and from DVB) As far as I can tell, MinimServer will support these files, but I need to rename the extension from mp2 to mp3 to get that to work. mp3tag seems happy to tag the files with either extension.

I could simply convert the files to flac format, which would make handling them easy, at a cost of disk space, and have the advantage of making it easier to support my non-compliant mpeg1 audio renderer (a google chromecast audio). Alternatively, I could use on-the fly transcoding to .wav format from mp2/3. I don't have any mp3 files, so it wouldn't matter that I was pointlessly transcoding those, although it would prevent the use of my Pure DAB radio, whose wifi isn't reliably up to the bit rate of a 48kHz wave file, but is ok with a 192kb mp2 stream.

I should add that there are no advantages for editing (that is trimming for the part I want) in converting to a different format, lossless cutting works well with mp2 files.

I don't think there's any particularly elegant solution. The best I could think of would be to have a feature in MinimServer that allowed you to define transcoding rules by renderer name. I'd choose name because the reported capabilities often aren't accurate, or in the case of mpeg 1 audio compliance aren't available, and in any case, there may be other reasons such as available connection speed, or tailoring of the sound for specific systems.

e.g.
my portable radio: everything to 44/48kHz 256kb mp3
my living room stereo: everything to (tuned) wav
my chromecast audio: mp2/3 to flac
anything else: as the renderer (claims to) support

I think I could achieve (more or less) this, by running multiple instances of MinimServer preferably with carefully tailored outgoing firewall rules, but that doesn't seem attractive.

So, I was wondering whether any community members have considered this problem, and if so what they have done or would suggest.
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28-07-2017, 22:53
Post: #2
RE: mpeg1 layer 2 audio (mp2 or m2a) files
The UPnP protocol doesn't permit the server to change the transcoding target type depending on what renderer you are using. This is because the server is required to state the stream MIME type to the control point before the control point has selected the renderer. By the time the control point has selected the renderer and the renderer has contacted the server, it is too late for the server to change the stream MIME type.
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29-07-2017, 12:44
Post: #3
RE: mpeg1 layer 2 audio (mp2 or m2a) files
I ended up transcoding all my mp2 files to flac. It always feels wrong to keep lossy data in a lossless container, but in the end it was just easier. But mp2 was a relatively small part of my library; I might have tried harder if it were a larger part.
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