January 6, 2014 Leave a comment
Some users of Skype for Linux have reported that the bottom half of the received video image is corrupted in installations that use the closed-source video driver for ATI GPUs (the AMD Catalyst proprietary Linux driver, also known as the ‘FGLRX’ driver). One user described the lower half of the video image as “covered in small coloured squares like a chequer board”.
From what I have read in a few forums, it seems the problem does not occur when the open-source Radeon driver is used. My own experience corroborates that: I use the Radeon driver on one of my laptops, and received video in Skype is fine.
My main laptop has an AMD ATI Mobility Radeon HD 5650 GPU and I am using the Catalyst driver under Gentoo Linux. In this case there was a problem with received video in most Skype sessions. Either of the following effects usually occurred:
As shown in Snapshot 1, the lower half of the received video image was covered in a grid of thin green lines with areas tinged with purple, blue or green, whereas there was no grid of lines in the upper half of the image but some areas were tinged with red or blue.
As shown in Snapshot 2, the lower half of the received video image was covered in a grid of thin red lines, with a purple tinge in some areas, whereas there was no grid of lines in the upper half of the image, which looked reasonable but had some red-, green- or blue-tinged areas.
In all cases Skype’s thumbnail of my Webcam’s video image looked fine, and the person on the other end of the call said the video image received from me looked fine too.
Because of a bug in a previous version of the Catalyst driver a few years ago — see my blog posts Playing QuickTime videos in Firefox and Chromium + XVideo bug in AMD Catalyst 11.11 and 11.12 driver and AMD Catalyst for Linux driver 12.2 fixes the XVideo bug that crashed X.Org Server 1.11.x — I happen to know that Sykpe uses X11 overlays with the XVideo extension (xv), rather than using the OpenGL renderer (gl) or X11 with the SHM extension (x11). This made me wonder whether the use of XVideo with the Catalyst driver was causing the current problem. Unlike media players such as MPlayer and VLC, it is not possible to configure Skype to use gl or x11 instead of xv, so I thought it would not be possible to test whether the use of gl or x11 instead of xv would make a difference. Until, that is, I came upon a ‘trick’ posted by openSUSE user queequeg in 2009 during the period when an earlier version of the Catalyst driver had the aforementioned bug:
Anybody trying to make a video call with Skype and ATI fglrx drivers has had problems due to Skype using the “xv” video mode with the driver can’t handle. For anyone interested that is affected by this, there is a workaround:
1. Run the xvinfo command and look at the number of xv sessions available. Some cards have only 1, some have as many as 4. This is the number of xv occurances that the card can do at one time.
2. “Use up” all these xv sessions by opening videos in your favorite video player making sure to use xv for the video output. The videos can then be paused.
3. Once this (or they) are open, skype can be started and will default to X11 video and work properly with video calls.
I know this is a goofy way to get around this issue, but until fglrx can handle xv or skype allows an option to choose X11 for video render, I don’t know of any other way to do it.
(From what I hear, the 11.1 fglrx drivers can handle xv, but I haven’t confirmed this.)
So I tried his work-around. I had to launch four media players in order to use all available XVideo sessions. Lo and behold, when I launched Skype and made a video call the received video image was perfect. So it appeared that the Catalyst driver is not able to handle well the XVideo output from Skype. However, playing and pausing four videos every time I want to make a video call in Skype would hardly be practical, would it? And that is not the only downside: when I maximised a Firefox window during the Skype video call, my laptop spontaneously rebooted (I assume the X.Org server crashed).
I did also wonder whether just disabling compositing would solve the problem, so I disabled KWin Desktop Effects, but that didn’t make any difference.
I had also read in several forums that enabling or disabling the TexturedVideo and/or VideoOverlay options in the xorg.conf file have an effect on the video image produced by the Catalyst driver, but I could not find a post mentioning the use of either of those options to fix the specific problem I was seeing. So I decided not to pursue the xorg.conf route.
In my searches of the Web I came across a post somewhere that mentioned using GTK+ UVC Viewer (
guvcview) to adjust video properties and improve video in Skype. I thought
guvcview was only for adjusting the video image from a Webcam connected to my machine, i.e. adjusting the outgoing video image, and would not have any effect on received video. Nevertheless, I decided to install and launch
guvcview to see if I could adjust both incoming and outgoing video properties. To my surprise,
guvcview appeared to have fixed the problem with the received video. These are the steps I followed:
- I launched Skype and started a video call. The received video image had a grid of thin red lines and purple/green/blue tinting (similar to Snapshot 2).
- I Installed
guvcviewusing the package manager.
- I launched
guvcviewin a Konsole (terminal) window. After
guvcviewcreated the file
/home/fitzcarraldo/.config/guvcview/video0and checked various video and audio settings it exited because my Webcam was being used by Skype (‘
libv4l2: error setting pixformat: Device or resource busy‘).
- I clicked on the Webcam icon in the Skype call window, to turn my Webcam off.
- I launched
guvcviewagain. The lower half of the received video image in Skype changed from a grid of thin red lines to a continuous green-coloured band, and the upper half of the image now looked reasonable but still had some red- or blue-tinged areas (see Snapshot 3 below).
- On the ‘Image Controls’ tab in the ‘GUVCViewer Controls’ window I changed the video frequency from 60 Hz to 50 Hz then back to 60 Hz again. I was just tinkering, and I believe this had no bearing on the outcome.
- I clicked on the ‘Quit’ button in the
guvcviewwindow to terminate the application.
- I clicked on the Webcam icon in the Skype call window to turn on again the Webcam, and the received Skype video image changed to a perfect image (see Snapshot 4 below).
It appears that
guvcview had an effect on the received video image in Skype, although, if it did, I do not understand how. To check if the fix was permanent I ended the Skype video call, signed out of Skype and quit the application, rebooted and made a new Skype video call. The received video image in Skype was again perfect. I even deleted the
guvcview configuration file and repeated this check, just in case the configuration file was somehow being used even though I had not launched
guvcview, but the received video in yet another Skype video call was still perfect. I also clicked on the Webcam icon in the Skype call window several times during each call in order to turn my Webcam off and on several times; the received video image of the other person remained perfect.
So there you have it: when using an AMD ATI GPU and the Catalyst driver, it seems that
guvcview can be used — at least in my case — to eliminate the type of image corruption in received Skype video shown in Snapshots 1 and 2. So, if you are also using the AMD Catalyst for Linux driver and are experiencing a similar problem, try
guvcview. It might just do the trick.