mpv step forward is fast but step back is slow

in mpv keyboard shortcuts:

.      Step forward. Pressing once will pause, every consecutive press will play one frame and then go into pause mode again.
,        Step backward. Pressing once will pause, every consecutive press will play one frame in reverse and then go into pause mode again.

Step forward is faster but step backward is slow. Because i am using some lua scripts to trim video.

how to make both work easily.

If i re encode the video to mjpeg format then it its vert smooth

Playing back prores (all I-frame) shows the same behaviour.

Djvview has the option of caching decoded frames in memory, is this possible with mpv? Maybe with a user specifiable RAM cache, like djvview? I use mpv for previewing renders and so on, the ability to smoothly play backwards would be really useful.

http://djv.sourceforge.net/

--demuxer-seekable-cache=yes --cache=yes --demuxer-max-back-bytes=10000M --hr-seek=yes --demuxer-cache-wait=yes

In addition to the tip above I could seek precisely in mts streams using the --hr-seek-deumuxer-offset=1.5 option solved it.

wow u dev guys r0ck ~ what u write here and in man page !!

with play-dir hack, and tuning the demuxer options,
got it to work with 4K HEVC x265 smooth backwards playback,
video synced with reverse audio, using cpu or gpu decode : -)

best video player feature ever ; -)

cache=yes
demuxer-readahead-secs=60
demuxer-seekable-cache=yes
demuxer-max-bytes=1000MiB
video-reversal-buffer=500MiB
audio-reversal-buffer=200MiB
demuxer-max-back-bytes=700MiB
hwdec-extra-frames=256
demuxer-cache-wait=yes
#hr-seek=yes
#demuxer-backward-playback-step=

what might be nonsensical in the above config?

thx 4 all the code

--demuxer-seekable-cache=yes --cache=yes --demuxer-max-back-bytes=10000M --hr-seek=yes --demuxer-cache-wait=yes

I don't know why this has so many positive reactions, doesn't look like it did anything. Doesn't mpv use a cache already? Increasing the cache size doesn't do anything. Depending on the video, stepping back , continues to take on second or more, yet stepping forwards is instant. seek -0.05 exact is just as slow too. These configurations don't change that mpv still does what @/Mia-0 said at the start of the thread, mpv has to decode forwards since the last keyframe to find the frame just one frame ago.

I would prefer if mpv could have a small cache of previous frames.

with the options i mentioned, it works for me on most video files to go any direction one frame. there is even a hotkey for playing backwards. and that works instantly u can go back and forth in video in any playback speed. if its 4k and x265 one needs a GPU that supports that decoding. in my simple setup mpv can play most video files any speed and any direction. even with reverse sound and pretty instant no delay. hook up a usb playstation controller to controll it, and it is the coolest media player ever. have to experiment with tuning these options to your system though ;)

with the options i mentioned, it works for me on most video files to go any direction one frame. there is even a hotkey for playing backwards. and that works instantly u can go back and forth in video in any playback speed.

Those sets of options don't do anything for me. This might depend on the video codec and mpv configuration. I will test with a sample video and report back. Meanwhile I came up with a funny hack:

, cycle-values play-dir - +
. frame-step

ah yes with ur file Buck Bunny single step back is about half the framerate of single frame forward.
but what works for me as a hack is, switching to reverse playback mode, and then single step forward :)

Meanwhile I came up with a funny hack:
, cycle-values play-dir - +
. frame-step  

That's a great hack, it works like a charm, thanks! However, I think the . frame-step might be unnecessary? I've tried with and without it and there's no difference, I'm not sure I understand why it's used here.

Meanwhile I came up with a funny hack:
, cycle-values play-dir - +
. frame-step  
That's a great hack, it works like a charm, thanks! However, I think the . frame-step might be unnecessary? I've tried with and without it and there's no difference, I'm not sure I understand why it's used here.

Yeah . frame-step is the default already, I just included it as a reminder.

Update step-back keybind

I fixed by uncommenting the RIGHT seek 5 and LEFT seek -5 lines in input.conf
and also by adding hr-seek=yes in mpv.conf

Those sets of options don't do anything for me. This might depend on the video codec and mpv configuration. I will test with a sample video and report back. Meanwhile I came up with a funny hack:
, cycle-values play-dir - +
. frame-step               

This is cute, but is it possible to create a faster keybind to only step back one frame by switching the direction, doing a frame-step, then switching direction again?
I tried , set play-dir -; frame-step; set play-dir +, but it does not work as expected.

play-dir - need to cache frames in memory, and changing direction of play probably kills previous state.

sorry to necro this but i got really annoyed by the slow , backstepping that i made a script to "fix" it

backstep.lua

-- backstep.lua
--
-- Faster frame-back-step for mpv

local mp = require('mp')

function change_direction(direction)
	if mp.get_property('play-direction') ~= direction then
		mp.command('cycle play-direction')
		osd_message = string.format('P: %s', direction:gsub('^%l', string.upper))
		mp.osd_message(osd_message)
	end
end

function frame_step(event, direction)
	change_direction(direction)
	if event.event == 'down' or event.event == 'repeat' then
		mp.command('frame-step')
	elseif event.event == 'up' then -- counters imprecision of 'repeat'
		mp.set_property('pause', 'yes')
	end
end

mp.add_key_binding(nil, 'frame-forestep', function(event)
	frame_step(event, 'forward')
end, {complex = true})

mp.add_key_binding(nil, 'frame-backstep', function(event)
	frame_step(event, 'backward')
end, {complex = true})

mp.add_key_binding(nil, 'fore-play', function(event)
	change_direction('forward')
	mp.command('cycle pause')
end)

input.conf changes

# backstep.lua - frame stepping
, script_binding frame-backstep
. script_binding frame-forestep

# backstep.lua - pause cycling
MBTN_RIGHT script_binding fore-play
p script_binding fore-play
SPACE script_binding fore-play
PLAY script_binding fore-play
PAUSE script_binding fore-play
PLAYPAUSE script_binding fore-play

there's just a few issues:

prolonged or too much playback on play-direction backward can sometimes cause reversal frame queue overflow
- i've read that increasing video-reversal-buffer or demuxer-max-back-bytes helps but it can still occur every now and then
it's prone to audio-video desync
it takes two inputs to properly begin stepping frames after changing play-direction (i never understood why) but it's better than waiting 20 seconds just to go back 5 frames
- in case you want to observe this, add a line to your osd-status-msg to display video frame count like so:

nvenc_h264_1080p_Q25.mp4

despite the small problems, it's more than enough for my use case, i hope this helps(:

@nucspl

@nucspl Awesome script, thank you :)

@nucspl

@nucspl Hi, the solution for me is to not use the scripts forward seeking and just leave it at default, and only keybind the backward seeking to the script. This way you don't have to press the key twice. Awesome script, thank you :)

mpv seek
. frame-step
#, frame-back-step
script seek
, script_binding frame-backstep
#. script_binding frame-forestep

sorry to necro this but i got really annoyed by the slow , backstepping that i made a script to "fix" it

backstep.lua
input.conf changes
there's just a few issues:

prolonged or too much playback on play-direction backward can sometimes cause reversal frame queue overflow

i've read that increasing video-reversal-buffer or demuxer-max-back-bytes helps but it can still occur every now and then

it's prone to audio-video desync

it takes two inputs to properly begin stepping frames after changing play-direction (i never understood why) but it's better than waiting 20 seconds just to go back 5 frames

in case you want to observe this, add a line to your osd-status-msg to display video frame count like so:

nvenc_h264_1080p_Q25.mp4
despite the small problems, it's more than enough for my use case, i hope this helps(:

I used to use a script then reverted to using the mpv input file and playdir which worked much better. I will try your script and see what how well it works in comparison. Well worth the necro if it works. Even if it doesn't, it's definitely something that I hope one day can be improved :)

@netExtra

@netExtra what do you mean by playdir?

@netExtra

@netExtra what do you mean by playdir?

From the mpv manual

--play-direction=<forward|+|backward|->
Control the playback direction (default: forward). Setting backward will attempt to play the file in reverse direction, with decreasing playback time. If this is set on playback starts, playback will start from the end of the file. If this is changed at during playback, a hr-seek will be issued to change the direction.

It then goes on to explain why backward playback will usually be slow and always be problematic.

@nucspl

@nucspl Hi, the solution for me is to not use the scripts forward seeking and just leave it at default, and only keybind the backward seeking to the script. This way you don't have to press the key twice. Awesome script, thank you :)
mpv seek
. frame-step
#, frame-back-step
script seek
, script_binding frame-backstep
#. script_binding frame-forestep
sorry to necro this but i got really annoyed by the slow , backstepping that i made a script to "fix" it
backstep.lua
input.conf changes
there's just a few issues:

prolonged or too much playback on play-direction backward can sometimes cause reversal frame queue overflow

i've read that increasing video-reversal-buffer or demuxer-max-back-bytes helps but it can still occur every now and then

it's prone to audio-video desync

it takes two inputs to properly begin stepping frames after changing play-direction (i never understood why) but it's better than waiting 20 seconds just to go back 5 frames

in case you want to observe this, add a line to your osd-status-msg to display video frame count like so:

nvenc_h264_1080p_Q25.mp4
despite the small problems, it's more than enough for my use case, i hope this helps(:

I used to use a script then reverted to using the mpv input file and playdir which worked much better. I will try your script and see what how well it works in comparison. Well worth the necro if it works. Even if it doesn't, it's definitely something that I hope one day can be improved :)

I've just tried it and it's very smooth. But I still prefer playdir because I don't want to have to hold down the key all the time. So I'm modifying to play continuously in reverse to compare and since it's basically using the same mechanism, the results are the same. I'm also running through the SVP frame interpolation software. Without that, playdirection works perfectly well. With SVP both playdir and you script which uses playdir perform the same. But when holding down the key, that seems to get around the issue.

How do you keybind it?

I find this to be nice. Then you can still step back 1 frame if you need to.
/ cycle-values play-dir - +
. frame-step

One thing I wouldn't mind would be if MPV would use as many resources as it needs. My computer is barely jogging while MPV is lagging.

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mpv step forward is fast but step back is slow #4019

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mpv step forward is fast but step back is slow #4019

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