[FFmpeg-trac] #6975(undetermined:new): Recent change to sync video output to screen refresh conflicts with -noframedrop
FFmpeg
trac at avcodec.org
Mon Jan 22 11:03:02 EET 2018
#6975: Recent change to sync video output to screen refresh conflicts with
-noframedrop
-------------------------------------+-------------------------------------
Reporter: Misaki | Owner:
Type: defect | Status: new
Priority: normal | Component:
Version: git-master | undetermined
Keywords: | Resolution:
Blocking: | Blocked By:
Analyzed by developer: 0 | Reproduced by developer: 0
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Comment (by Misaki):
What probably happened is that ffplay now pays attention to the
{{{vblank_mode}}} environment variable. From
https://stackoverflow.com/questions/17196117/disable-vertical-sync-for-
glxgears
{{{
time ( time ffplay -autoexit -noframedrop black.mp4 )
time ( ffplay -autoexit -noframedrop black.mp4 )
}}}
real: 20 seconds
{{{ time ( vblank_mode=0 ffplay -autoexit -noframedrop black.mp4 )}}}
real: 13.4 seconds
I thought that {{{vblank_mode=0 time ffplay [...]}}} reduced it to 10
seconds, but what was actually happening was that I have an alias of
ffplay to 'ffplay -hide_banner -noframedrop', and for some reason the
temporary environment variable and 'time' makes it so the alias isn't
used.
I think it's enough though, and ffplay just doesn't speed late frames up
to 2x speed, only to 1.5x speed.
I assume this environment variable has been set this way for a long time,
since I was familiar with glxgears syncing to vertical refresh.
This may still be a bug, if users don't expect to have to deal with this
non-ffmpeg setting in order to get 60 fps videos to work with
-noframedrop.
--
Ticket URL: <https://trac.ffmpeg.org/ticket/6975#comment:1>
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