Transcoding combinations UPnP and Internet Radio

[simoncn]

(12-03-2015 12:19)Pastim Wrote:  I have struggling to understand the different transcoding combinations available. Apologies for the length of the following, but I would be grateful if someone could confirm, or correct, my understanding.

So this is an attempt to understand the subtleties of transcoding with UPnP and Internet Radio. I will only mention aac and 'unspecified' stream types where the underlying type is in fact aac, for the sake of simplicity. I believe other stream types will all follow the same logic as that for aac.

1. Internet Radio Only

If the only service used is Internet Radio, no transcoding should be specified at all. However, I believe a converter like ffmpeg or avconv may still be needed for HLS streams.

It shouldn't be needed for an internet radio, as this should be able to receive an untranscoded AAC ADTS stream (same as the previous BBC streams).

Quote:2. UPnP Streams Only

If the only radio service used is Internet Radio streaming via UPnP, then I believe the options are as follows:

a) aac is specified in the stream url or in the m3u file

This should always be specified in the m3u file, not by "hand-editing" the URL. If the URL doesn't match what's in the m3u file, the results are undefined. In what follows, I am assuming that it was specified in the m3u file.

Quote:aac:L16/wav24/-

- aac can be transcoded to any one of the supported output stream types (eg. L16 or wav24), and also made available unchanged (-). A '^' has no effect since the Control Point or Renderer makes the choice, not minimstreamer.

*:L16/wav24/-

- has no effect, since the codec is known

Correct.

Quote:b) aac is not specified, but minimstreamer finds out that it is aac on inspection:

aac:L16/wav24/-

- the Control Point or renderer will choose amongst the defined codecs

Not correct. The control point will see a single stream and MinimStreamer will choose L16.

Quote:
aac:L16/wav24^/-

- minimstreamer will always transcode to wav24 (I can't see why this is a useful combination, why not just use aac:wav24? )

Correct. It is a useful setting because you might have other streams of type a).

Quote:*:L16/wav24/-

- the Control Point or renderer will choose amongst the defined codecs

*:L16/wav24^/-

- as above - the '^' has no effect since '*' is specified

Correct.

Quote:3. Both Internet Radio and UPnP devices available

a) aac is specified in the stream url or in the m3u file

This should always be specified in the m3u file, not by "hand-editing" the URL. If the URL doesn't match what's in the m3u file, the results are undefined. In what follows, I am assuming that it was specified in the m3u file.

Quote:aac:L16/wav24/-

- for UPnP, aac can be transcoded to any one of the supported output stream types (eg. L16 or wav24), and also made available unchanged (-).

Correct.

Quote:- what happens for Internet Radio? Does it fail?

For internet radio, MinimStreamer will choose L16 (first in list). This might succeed if the internet radio can play an L16 stream.

Quote:aac:L16/wav24/-^

- for UPnP, aac can be transcoded to any one of the supported output stream types (eg. L16 or wav24), and also made available unchanged (-).

- for Internet Radio no transcoding will take place.

*:L16/wav24/-

- has no effect, since the codec is known

*:L16/wav24/-^

- has no effect, since the codec is known

Correct.

Quote:b) aac is not specified, but minimstreamer finds out that it is aac on inspection:

aac:L16/wav24/-

- for UPnP, minimstreamer will default to L16 – I'm not sure if the other values have any effect at all?

The control point will see a single stream and MinimStreamer will always choose L16.

Quote:- what happens for Internet Radio? Does it fail?

For internet radio, MinimStreamer will choose L16 (first in list). This might succeed if the internet radio can play an L16 stream.

Quote:aac:L16/wav24/-^

- for UpnP, minimstreamer will default to no transcoding – I'm not sure if the other values have any effect at all?

For this stream, the other values are ignored.

Quote:- for Internet Radio no transcoding will take place

*:L16/wav24/-

- for UPnP, aac can be transcoded to any one of the supported output stream types (eg. L16 or wav24), and also made available unchanged (-).

Correct.

Quote:- what happens for Internet Radio? Does it fail?

Internet radio will not be transcoded.

Quote:*:L16/wav24/-^

- for UPnP, aac can be transcoded to any one of the supported output stream types (eg. L16 or wav24), and also made available unchanged (-).
- for Internet Radio no transcoding will take place.

Correct.