Console gaming on a remote X display
I have recently ended up in a situation where creating something like this (see diagram) would allow me to play my Game Cube on my laptop display before I finalise my purchase of a nice new LCD display for my desktop system.
Game Cube -> Tv Card -> Linux Box (no display) -> 100Base-t Network -> Laptop (with display)
Playing a console game over a remote X display is slightly more challenging than simply watching TV. With TV you can capture your video and audio input, compress it, send it over the network in a nice format and decompress it at the other end. Sure, you’ll be watching TV that is maybe one second to a minute behind whats actually being broadcast but its in sync and it looks good. If you’re attempting to play a game in a similar fashion even 500ms (1/2 a second) delay would make most console games totally un-playable, with this in mind I set about console gaming over remote X with ssh.
It should be noted that:
- While attempting this I had no access to the internet, just to whatever documentation came with my debian / ubuntu installs
- My desktop runs debian testing and my laptop runs ubuntu edgy eft
- If you just want the solution, skip down to Attempt 4.
Attempt 1 - tvtime
Usually when playing Game Cube on a local display attached to my desktop I use a fantastic application called tvtime, To run this I SSH’ed from my laptop to my desktop with X display forwarding and compression enabled:
iain@laptop ~> ssh -X -C -o CompressionLevel=9 desktop
iain@desktop ~> tvtime
Unfortunately for me tvtime does not appear to work via X display forwarding, it appears to be looking for an xvideo port to connect to and fails upon startup, most likely tvtime was not designed for this.
Attempt 2 - xawtv
Xawtv is a tried and tested linux tv viewing tool, its almost guaranteed to work and it did:
iain@laptop ~> ssh -X -C -o CompressionLevel=9 desktop
iain@desktop ~> xawtv -remote
Attempt 3 - ffmpeg, mplayer, pipes & a network (madness)
After the failure of xawtv I had determined that the bottleneck was the network. I could see from my network / cpu utilisation graphs that the cpu was hardly getting used and the network was pegged at 100% usage. This made me think of compressing the video “on the fly” and then sending it over the network to my laptop - due to the latency involved in encoding this was not my greatest idea but getting it to work was an interesting experiment.
It was obvious that I needed to keep the latency as low as possible, this meant getting as few components in my encoding -> network -> decoding chain as possible. After the reading of some man pages I realised that ffmpeg and mplayer could encode and play from standard input / output, this sent the unix geek in me a little bit crazy. Even though the sane voice in my head was saying “this is stupid, its never going to work as you want it” but the unix geek in me simply retorted with “but wouldn’t it be cool if it worked!”. In the end unix geek won, it was a sad moment for my sanity.
Some time and many many command line arguments later, it was working. By using ssh keys to avoid any input on my part I had managed to redirect the standard output of a remote ffmpeg command over ssh and into the standard input of mplayer, the command looks something like this…
iain@laptop ~> ssh desktop “/home/iain/src/ffmpeg-0.4.9-pre1/ffmpeg -vd /dev/video0 -an -f mpeg1video -aspect 4:3 -tvstd pal - 2> /dev/null” | mplayer -
Attempt 4 - mplayer, or what should really have been Attempt 3
After reading the mplayer manual (the parts useful to me anyway) I noticed that mplayer could play from v4l2 (video for linux) devices. Hoping that it would employ a more intelligent technique than xawtv when displaying in full screen mode I set about configuring mplayer. It is fairly easy to configure and work with once you’ve found the relevant options, I opted to put the options in a config file (usually located in ~/.mplayer/config) instead of typing them each time I wanted to use a v4l device. The entry in the config file looks something like this:
tv=driver=v4l2:input=2:width=256:height=192:device=/dev/video0:normid=1:noaudio=1:fps=30
As you can see, that’s going to play at a fairly small resolution (256×192) and limit the fps to 30 with no audio. The steps to run this are fairly similar to xawtv:
iain@laptop ~> ssh -X -C -o CompressionLevel=9 desktop
iain@desktop ~> mplayer tv://
After mplayer had started and expecting the worst I tapped ‘f’ to put mplayer into full screen mode. Shockingly it worked, some how mplayer appears to get the remote x server to stretch the image to full screen size, keeping the source resolution fixed. This method works really well, I played about with some higher resolutions but the delay increased too much, 256×192 appears to be a happy medium. After several hours of gaming I’m happy to say that it is possible to play console games on a remote X display