How to change ffmpeg -threads settings

Question

Working on a tube site. I'm running videos through ffmpeg on a linux dedicated server to convert to mp4.

The server specs:

Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                8
On-line CPU(s) list:   0-7
Thread(s) per core:    2
Core(s) per socket:    4
Socket(s):             1
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 60
Stepping:              3
CPU MHz:               3491.749
BogoMIPS:              6983.49
Virtualization:        VT-x
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              8192K
NUMA node0 CPU(s):     0-7

Issue during testing is that even only doing 4-5 at once, the server load skyrockets to an average of around 36. This is just a single person. I imagine when it opens, many people will be uploading at once.

It seems ffmpeg tries to use all the resources available per conversion.

I've heard there's a -threads setting you can change, but I cannot find it. I have an 8 cpu server. It's only used for conversions, so I've heard the best setting would be between 2 and 4. I can test it out.

But how do I change this setting? Everything I see online discusses this setting, but not the steps to change it.

Answer 1

The option flag you want is really just -threads and you would use it like this (for just one thread):

ffmpeg -i somefile.wmv -c:a libfdk_aac -c:v libx264  -threads 1 transcoded.mp4

However, there are quite a few subtleties that will raise your server load and ops time, such as rescaling, applying filters and final frame quality / frame rate - not to mention the fact that some VM architectures actually read and write everything twice (once natively and once virtually!!!)

Here are a few tips to get your speed up:

1. use a queue, so that only one item is ever being transcoded at a time
2. request smaller files from your users
3. use the full horsepower of your machine by:
   • reading and writing from a ramdisk
   • switching to bare metal for transcoding tasks
   • use -threads 0

Whatever you do, keep your users informed about the transcoding process, because it just takes time. (I.J.T.T.)

[edited command to reflect LordNeckbeard's comment]

Answer 2

This may be a little old but this sounds like a perfect task for a container like docker.

• Let ffmpeg run with full horsepower (as denjello called it)
• but let it run inside docker

Now you can limit how much resources a single ffmpeg instance may consume without even using ffmpeg commandline options. And not just cpu but also memory and IOs.

Even more: Maybe you have different tasks that may run in the background and you don't care how long they take and you have tasks that should run fast, so you can put a weight on different tasks.

See https://docs.docker.com/engine/reference/run/#runtime-constraints-on-resources

There is already a predefined ffmpeg image on github: https://github.com/jrottenberg/ffmpeg

docker run jrottenberg/ffmpeg \
        -i http://url/to/media.mp4 \
        -stats \
        $ffmpeg_options  - > out.mp4

A single conversion will likely run slower because of the overhead but if you run mutliple instances concurrently this could be a huge benefit. Any this will scale very well, not to mention the improved security because each task is isolated from the underlying OS.