How many threads does ffmpeg use by default?

Solution 1:

it depends on codec used, ffmpeg version and your CPU core count. Sometimes it's simply one thread per core. Sometimes it's more complex like:

With libx264 it is cores x 1.5 for frame threads and cores x 1 for slice threads.

Solution 2:

As of 2014, it uses an optimal number.

You can verify this on a multi-core computer by examining CPU load (Linux: top, Windows: task manager) with different options to ffmpeg:

• -threads 0 (optimal);

• -threads 1 (single-threaded);

• -threads 2 (2 threads for e.g. an Intel Core 2 Duo);

• none (the default, also optimal).

2015 edit: on a 12-core CPU, some ffmpeg commands have Linux top showing at most 200% cpu (only 2 cores), no matter what number is given to -threads. So the default may still be optimal in the sense of "as good as this ffmpeg binary can get", but not optimal in the sense of "fully exploiting my leet CPU."