[Icecast] Delay on preroll

[Geoff Shang]

On Wed, 4 Dec 2019, Javier Fuentes wrote:

> I have a problem when I use the intro to send a pre-roll, the main stream
> generates a 20 second delay, when the main stream is played it has no delay.
> Is there any parameter I can use to eliminate the delay?
> with pre-rolli: https://radiomarca-rrcast.flumotion.com/radiomarca/live.mp3
> without pre-rolli:
> https://radiomarca-rrcast.flumotion.com/radiomarca/live-np.mp3

Are you saying that the listener is further behind on the stream with the 
pre-roll?

I believe that this happens because the pre-roll is sent as quickly as 
possible by Icecast to the client, rather than at the rate of the audio. 
So it will take much less time to send than it does to play.  Once it has 
finished sending the pre-roll, it starts sending the live audio.  The 
player still has to play the pre-roll and will therefore be further behind 
the live audio when it gets to it.

Note that I'm only guessing but it makes sense.

My advice, use a shorter pre-roll.  As a listener, this will get very 
annoying very quickly.  40 seconds is a long time to listen through a 
pre-roll if your connection drops for a second.  I would limit it to 10 
seconds max.

BTW: At time of writing, the live audio is out of phase (see 
https://www.audiocheck.net/audiotests_polaritycheck.php for explanations 
and examples).  this will cause the encoder to work much harder than it 
has to and will not sound as good as it should.  It will also cause anyone 
listening through a single speaker not to be able to hear the announcer 
and anything else that is panned centre (e.g. song vocals).

this is most likely caused by an incorrectly wired cable or an RTS plug 
which is not fully inserted into the jack.

HTH,
Geoff.