On Sun, Apr 25, 2010 at 02:10:49AM +0200, Lennart Poettering wrote: > > A solution acceptable from VM_HOST's point of view on security is: > > 1) Load module-simple-protocol-tcp in VM_HOST > > 2) Run pulseaudio daemon in VM_USER (and make users connect to it, instead > > to VM_HOST). Load module-pipe-sink, and pass the pipe output over the network > > to port 4711 in VM_HOST (to module-simple-protocol-tcp code). > > That is not workable, as this provides no timing info at all. Video will > be jumpy, and with uncontrolled latencies. What do you think about implementing synchronization by enforcing low buffer size ? [yes, I am aware of http://www.pulseaudio.org/wiki/LatencyControl, but it hardly applies in this case] Tested setup involves: 1) Patch parec-simple and pacat-simple http://0pointer.de/lennart/projects/pulseaudio/doxygen/parec-simple_8c-example.html http://0pointer.de/lennart/projects/pulseaudio/doxygen/pacat-simple_8c-example.html so that they read/write to vchan, not stdin/stdout. Vchan is an interVM pipe, practically latencyless, with only 1024 bytes of internal buffers (it will block if written to more) 2) In parec-simple, change the buffering parameter (in the call to pa_simple_new) to {.maxlength=8192, .fragsize=1024} 3) run parec-simple in VM_USER (it will fetch from auto_null.monitor I assume) 4) run pacat-simple in VM_HOST. The above works fine, at least when judging by a nontrained ear. Note that if we do not patch to use vchan directly, but use vanilla tools and pick data from their stdout/stdin instead, the buffering introduced by the stdin/stdout pipes results in noticeable delay between sound generation in VM_USER and reception in VM_HOST. Known downsides: 1) About 10% of CPU time overhead, because of frequent I/O due to small buffers. 2) Risk of dropouts Let's say 1) is acceptable (and can be probably lowered by tweaking buffer sizes); 2) should be mitigated by elevated scheduling priority ? Do you have any comments ? Particularly, do you see any scenario when desynchronization can occur ? RW
