Multiple devices/instances connected in wi-fi

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Multiple devices/instances connected in wi-fi

Postby vespadj on 07 Sep 2015, 10:52

After reading various threads I would like to purpose my point of view.


Assume that you have a tablet for play, and a phone to pre-listen and/or store music.
In tablet you can active wi-fi Tethering (also without internet) and became IP

1. Pre-Cue listening via Wi-Fi
In the meanwhile we waiting for "USB OTG Audio 2 stereos", if in a dj-set the stereo is much important then precise mix, the solution may be to stream pre-cue listening via wi-fi (link to the same suggestion:
It could be a experimental option in setting, choosing quality of pre-listening (mono/stereo, bit, ...) for then reduction of latency, then the visual waveform complete the accuracy of cue point.
RTP or HTTP protocol or similar, compatible with low performance devices (everybody has once).

2. Connect to music archive/db on a second instance/device.
Now, if you have two devices, probably you synch your music archives, then you Scan and Analise for each device.

My second suggestion is connect to another instance of CrossDJ (or a dedicated app) in the LAN (I mean, wi-fi Tethering, see preamble), using the usual browser rules after selection of source "CrossDJ on Xxxx...". Main instance queries title/bpm on the second instance (its own database), then load mp3 and analysis file (waveform and cache) via LAN to RAM, play, save new cuepoints or analysis to the second database, and also already-played flag.
Another thread on this arguments:

3. BPM-synch via wi-fi.
To complete the scenery of a mixer and two devices with CrossDJ, that browser the same archive, the next step is to synch decks via LAN.
Main music on my device crops a little sometimes during browsering and loading of the next track; so I could be use tablet and phone in One-Deck mode, with the new BPM-synch via LAN, it could be help.

Thanks for attention.
Comments are welcome.

Vespadj - Android user - Italy
Posts: 19
Joined: 07 Sep 2015, 07:24

Re: Multiple devices/instances connected in wi-fi

Postby RoJeC on 07 Sep 2015, 12:53

Thanks for sharing your thoughts.

Main issues with your wifi solution is the latency. First of all Cross cannot make a tethering exclusive feature. So any WiFi should work. Here is the problem that shared accespoints may result in low bandwidth.
Other limitation is that adding a device in the routing will have a difference in latency by definition. So when you e.g. add Main into the headphone signal it will have a delay versus main live.
Third it's not just hardware but also the 'driver of the soundcard' should be capable of handling 4 channels (2 stereo). And it should be able to send to different outputs.
And be aware that it has to work properly for almost all tab/phone combinations...

Regarding sharing tracks a bit similar story. Relying on WiFi isn't really possible in live performance.
Also syncing is not as easy as it seems. Currently the mediabase is used. If a seperate database would be in use it would take quite some space. The mediabase isn't easy to sync (as just tracks syncing won't make the fully synced environment).

Likely using OTG to the full is the route to follow for development. Since Lollipop it is supported, provided the manufacturer added both the hardware as the OS feature to the devices.


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Re: Multiple devices/instances connected in wi-fi

Postby vespadj on 07 Sep 2015, 16:42

I'm happy you understand what I mean.

1. I know about Latency problem (it could be seconds in streaming) but for searching a start cue point , it's better than no audio and only waveform visual aid only. But if Android 4.x needs 'driver of the soundcard' for gesture a background second stereo (3rd and 4th chs) , this problem can not be resolved in anyway. :(

2. I root my tablet and look in db. I see about soundcloud and collection, so how tracks are indexed (media of system). Synchronization of db is not my request (like someone ask) (and I just do it refered by _data field :D ), but I told about use one instance like archive and db (server) and another like client. Client talks directly* to server db.
*: info via JSON , mp3 and cache files tranfering.
Yes, I could be slow, but faster than soundcloud. And cuepoints may be reused.

3. BPM synch via LAN. Some software do it but I never test it, I don't know if they use UDP or TCP, or some calculation of the communication delay. But I would be very cool!
if point 2. and 3. would be avaible + a mixer, point 1. is not necessarily so.
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