How to change ffmpeg -threads settings

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]

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.