The run-time overhead of threading "seems to be negligible in typical cases" and this FFmpeg multi-threading is great news considering this multimedia library is used practically everywhere.
The mailing list announcement notes:
"You should see significantly better CPU utilization/wallclock speedup on multicore systems whenever transcoding isn't dominated by a a single component and the components aren't themselves already multithreaded."
Given the dominant use of FFmpeg throughout the industry and today's increasingly high core count servers, the culmination of this work landing certainly can't come soon enough.
Those interested in this FFmpeg multi-threading support can see the FFmpeg-devel mailing list . I certainly can't wait for this to land in FFmpeg Git and look forward to benchmarking it.