philippe_44 wrote:
> Let me try to explain and if you tell me how to tell the story in better
> english, that would be great:
>
> pcm = raw uncompressed audio data, no header to describe what the data
> are
> wav = file containing uncompressed audio data, but with a header to
> describe sample rate, size and channels. On 2+ bytes sample size, least
> significant byte is sent first
> aif = same as wav, but byte order are reversed
>
> When using compressed, self described formats like mp3 and flac, LMS
> sends the header of the file together with the audio data, so the
> receiving player extract critical information like channels, sample rate
> and size are read from the header.
> When using uncompressed format, LMS only sends raw pcm, without a
> header, just bytes. The critical parameters like number of channels,
> sample_size and sample_rate are sent in a LMS protocol separated
> message.
>
> On their side, and for uncompressed data, UPnP players can receive a
> stream made of either raw pcm, wav or aif.
>
> When receiving raw pcm data, sq2u could ideally, just forward it to the
> UPnP player and that would be easy ... except that some players do not
> support raw pcm, it must be encaplusated into a wav or aif file. Some
> support all options, some pcm and aif, some wav and aif, some pcm only,
> some wav only etc ... all permutation and combination
>
> So what sq2u does is adding a header on-the-fly when players do not
> allow raw pcm data. One of the difficulty here is that these wav and aif
> format header requires the "full file size to be set" and obviously I
> don't know it.
>
> So, when a UPnP player supports pcm, wav and aif, what to send ? the
> easy answer is pcm but sometimes UPnP players accept more rate and
> sample size combination through wav than through pcm (I know, this
> sounds silly ...). On top of that, when LMS sends raw pcm from a wav
> file and sq2u forwards that as raw pcm, it requires byte re-ordering
> which is CPU-consuming for nothing, really. Using wav could have avoided
> that
>
> So the idea here is to let the user specifiy the uncompressed format he
> wants to try to send to its UPnP player AND with which order of
> preference (don't worry, ultimately only supported format will be used).
> The Byte Ordering option is also to allow sq2u to choose, in the
> authorized list, the format that avoid byte-re-ordering. When disabled,
> the first format that is accepted by the UPnP player is used
>
> Does that help ?
Somewhat. However, as a relatively ignorant user I'm still not sure
what are valid combinations in all 3 fields. So:
- codecs can be pcm, mp3, flc and aac only? Is that right? And only
those specified will be used, in the order specified - is that right?
('pcm' here effectively means 'raw')
- if the pcm codec is chosen, it can effectively be sent in one of 3
forms - pcm, wav or aif in the RAW format preference - is that right? If
left blank, sq2u will work it out to be the most efficient - if any
other codec is chose from the valid set above, this field is irrelevant
- the byte order baffles me, but I assume sq2u will sort it out - I'm
not sure in what use-case I would want to specify it myself
Note I use pcm on one of my renderers because it is full specified (by
the player) and supported, but on my other one it is not so I use wav on
that one
LMS 7.9 on VortexBox Midi, Xubuntu 14.04, FLACs 16->24 bit,
44.1->192kbps. LMS plugin UPnP/DLNA Bridge to MF M1 CLiC (to MF amp &
ESLs) & Marantz CR603 UPnP renderers. Minimserver (server) & upplay
(control point) to same & to upmpdcli/mpd PC renderers. Squeezelite to
Meridian USB Explorer DAC to speakers/phones. Wireless Xubuntu 15.04
laptop with firefox/upplay or Android 'phone with
Squeeze-Commander/BubbleUPnP controls LMS/Minimserver. Have a Touch
with EDO, plus spare, but unused.
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