[winswitch] Xpra man page confusion: compression level and compressor

Antoine Martin antoine at nagafix.co.uk
Mon Jun 1 08:31:54 BST 2015

On 29/05/15 12:15, Jiang Qian wrote:
> Perhaps I am missing something, but this line in the entry about
> --compress=LEVEL in the manpage of xpra confuses me:
> "If lz4 compression is available, it will be enabled *when the level
> is set to 1*, lz4 compresses a lot less than zlib but it is also much
> faster."
I have updated the man page to try to make it clearer:
lz4 and lzo only support compress=0 (disabled) and compress=1 (enabled).
> I use RBG encoding, and I certainly have lz4 compression available. I
> enable them in command line by "--encoding=rgb --compressor=lz4"
> Does that mean I need to put "--compress=1" to set compression level
> to 1 in order for xpra to use lz4? What will happen if I put
> --compress=0 --compressor=lz4?
With "0", the compressor will be ignored.
> What about
> --compress=3 --compressor=lz4?
The result with be the same as "--compress=1"
lz4 does not have levels yet, though this may change in the future:
> I am using xpra over a gigabit lan, but on a weaker client side
> processor (the server have very powerful processor). I want rgb for
> display quality. I watch flash videos (e.g. nytimes, daily show) that
> are too slow to play on the client side, obviously with sound.
Note: your videos are already lossy and subsampled when sent to you over 
the Internet, so it is usually best to select the h264 (or vp9 encoding 
with xpra 0.15.x): the video encoding should be used for the video area 
and rgb (or png or whatever) should automatically be used for the rest.
Unless you are absolutely certain that you are CPU constrained and have 
bandwidth to spare.
> So are
> --encode=rgb --packet-encoder=rencode --compress=1 --compresspr=lz4
> --speaker-encoder=wav
> the best options to have?
It also depends on the video size and refresh rate.
480p at 30fps should be fine without any compression at all, but lz4 
will save tons of bandwidth for very little cost.
For 1080p on the other hand... you will probably need h264 (preferably 
via nvenc, but x264 will do too) on its highest speed setting (100). The 
video encoders are extremely efficient, and often underestimated.
Also make sure your client has OpenGL enabled, as this speeds up the 
displaying of your video, which allows for more time doing the decoding 
/ decompression / network.
>   Right now there are occassional lags and out
> of sync in sound.
The syncing of audio and video should land in the next release:
>   I'm running 0.14.24 on both server and clients, both
> running Ubuntu 14.04. I only forward individual window, not whole
> desktop. And yes, I use xvfb.
Try 0.15.0 ;)

> Thanks in advance for any advice.
> Regards
> Jiang
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