7 Oct
2020
7 Oct
'20
9:23 p.m.
does anyone know the right ffmpeg or mencoder commands to speed up an MKV video
file by 20X while reducing its file size accordingly? Bonus if it doesn't take
twice the lifetime of the universe to do it
thank you!
-jake
7 Oct
7 Oct
11:19 p.m.
Hi Jake,
According to my notes...
To double the speed of a video:
$ ffmpeg -i input.mp4 -filter:v "setpts=0.5*PTS” output.mp4
Use -an to disable audio:
$ ffmpeg -i input.mp4 -filter:v "setpts=0.5*PTS" -an output.mp4
Use 0.333 instead of 0.5 for 3x speed. 0.05 for 20x.
cheers
-Carl
8 Oct
8 Oct
8:59 a.m.
On Wed, Oct 07, 2020 at 11:19:36PM -0700, Carl Gorringe wrote:
Some other tricks to squash file size:
If you don't need to do any seeking during playback and the scene is
mostly static, you can extend the keyframe interval with encoder
parameters. You can also tweak the quality target with crf (0 to 63,
higher is lower quality):
$ ffmpeg -i input.mp4 -an -filter:v "setpts=0.125*PTS" -c:v libx264 -x264-params
"keyint=1000:crf=27" out.mkv
And if the contents of the video have truly static portions (like a
screencast, for example), you can use the "-tune animation" option.
For encoding speed, I think the libx264 encoder uses all threads by
default, but there is a -threads N option if it doesn't.
--Sean
9 Oct
9 Oct
1:11 p.m.
OMG thank you so much, this is great help everyone!!!
some operations take a long time and some are quicker, i'm trying to hone in on
the ones that are quick and dirty, rather than re-encoding everything. It's so
hard to understand the documentation!!!
I'll try these commands and take notes on what works and what doesn't. Feel
free to let me know if you're interested in the results!
one thing i've been working with is that i'm doing concatenation at the same
time... so much obscure arcane procedure that you just find on the web and try
until it works.
And i was having troubles until i realized that the hard drives in the server I
was accessing were slowly dying off from overheating...
On Thu, 8 Oct 2020, Sean Greenslade wrote:
1:49 p.m.
On Fri, Oct 09, 2020 at 01:11:12PM -0700, Jake wrote:
Yeah, FFMPEG can be pretty intimidating. Unfortunately, in the case of
doing time lapses, you almost certainly need to re-encode the video. The
one exception would be if your desired speedup exactly matches the rate of
i-frames in the source video. Then you could make a custom script that
just dropped all the p-frames. I have some code that could probably be
adapted for that if you're interested.
I'll try these commands and take notes on what
works and what doesn't. Feel
free to let me know if you're interested in the results!
Yeah, show us!
Concatenation can be tricky. Make absolutely sure all the source videos
have the same format / resolution.
And i was having troubles until i realized that the
hard drives in the server I
was accessing were slowly dying off from overheating...
Lol, yup, hard drives can get pretty toasty when they're being
stressed. Make sure your servers have fans pointed at the drives.
--Sean
2:46 p.m.
the computer i was doing these experiments on had a failed hard drive and got
taken out of service and now the corporation is going through a failure
analysis process to study how hard drives fail at high temperatures.
I have advised that the recording system be reconfigured to save data at the
target framerate rather than do transcoding, since the latter seems
impractical.
but i'll bring updates when i have them
On Fri, 6 Nov 2020, hol(a)gaskill.com wrote:
8 Oct
8 Oct
1:56 a.m.
I'm not sure if it can do what you ask, but I would guess that Shotcut can. It's
free, open source video editing software, and easy to learn, with plenty of online video
tutorials.
Mitch
________________________________
From: sudo-discuss <sudo-discuss-bounces(a)lists.sudoroom.org> on behalf of Jake
<jake(a)spaz.org>
Sent: Wednesday, October 7, 2020 21:23
To: sudo-discuss(a)lists.sudoroom.org <sudo-discuss(a)lists.sudoroom.org>
Subject: [sudo-discuss] how to speed up a video file and reduce its size?
does anyone know the right ffmpeg or mencoder commands to speed up an MKV video
file by 20X while reducing its file size accordingly? Bonus if it doesn't take
twice the lifetime of the universe to do it
thank you!
-jake
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participants (5)
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Carl Gorringe -
hol＠gaskill.com -
Jake -
Mitch Altman -
Sean Greenslade