[Solved] Choppy playback when dual monitors enabled

drcouzelis · 2017-12-23 14:59:29

I have two "monitors" connected to my desktop: my primary computer monitor, and my TV. I toggle the TV on and off, depending on when I want to watch something.

Sometime within the past month(?) something changed, and now mpv stutters / has choppy playback when both monitors are enabled. This is a new behavior, it has been smooth and "just worked" for years.

If only the TV or only the monitor are enabled (using xrandr) then the video plays smoothly. But if both of them are on, then the framerate drops drastically. It seems to depend on the scene, but I'd eyeball it at about 10 fps maybe?

I have a Radeon HD 5450, using the open source drivers. I've been using this setup for months, and this video card for years.

...Do you have any idea what could be causing such choppy playback when both monitors are enabled, something that used to work perfectly?

EDIT: I just noticed, smaller videos seem to play smoothly all the time... A low resolution h264 file will play smoothly, but a high resolution h264 file won't.

Last edited by drcouzelis (2017-12-23 16:36:12)

R00KIE · 2017-12-23 16:07:52

Make sure that you are not telling mpv to use something they have deprecated upstream (check mpv's console output and your configuration file) and thus making mpv use software decoding or use some slow video path.

Another option is trying the last 4.13 kernel (or one that you are sure worked fine) and see if it starts working fine again, if it does your best bet is to bisect the kernel and complain upstream. If that doesn't work then the problem is caused by something else and it's going to be more tricky to find the culprit (more variables).

drcouzelis · 2017-12-23 16:36:00

R00KIE wrote:

Make sure that you are not telling mpv to use something they have deprecated upstream (check mpv's console output and your configuration file) and thus making mpv use software decoding or use some slow video path.

I ruled this out... I forgot to mention, both mplayer and VLC were also experiencing the issue.

R00KIE wrote:

Another option is trying the last 4.13 kernel (or one that you are sure worked fine) and see if it starts working fine again, if it does your best bet is to bisect the kernel and complain upstream. If that doesn't work then the problem is caused by something else and it's going to be more tricky to find the culprit (more variables).

Solved! You found a workaround! Linux kernel 4.13.13-1 works like a charm.

I tried the kernel before current, and the kernel before that one, which felt like a good test. But I didn't realize going "all the way" back a dozen versions is only one month's worth of kernel updates. Arch Linux, you're crazy.

R00KIE · 2017-12-23 17:32:58

It's not really solved, you have found the culprit but you haven't solved the root cause. The bug will persist unless you are lucky and the bug gets reported by someone else or fixed due to some unrelated work. If you have the time and will to do it, bisect the kernel to find the offending commit and report it upstream. Given that it is a regression, if you pinpoint the cause it should get attention and get fixed quite quickly (usually it does but it's holiday season now so it might take a bit longer).

seth · 2017-12-23 22:24:11

Check the CPU load across all processes and whether you maybe switched from radeon to amdgpu w/ the kernel update.

Arch Linux

#1 2017-12-23 14:59:29

[Solved] Choppy playback when dual monitors enabled

#2 2017-12-23 16:07:52

Re: [Solved] Choppy playback when dual monitors enabled

#3 2017-12-23 16:36:00

Re: [Solved] Choppy playback when dual monitors enabled

#4 2017-12-23 17:32:58

Re: [Solved] Choppy playback when dual monitors enabled

#5 2017-12-23 22:24:11

Re: [Solved] Choppy playback when dual monitors enabled

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