multithreading ffmpeg

spezticle · 05-18-2012, 04:26 PM

so i've been using

Code:

for f in *.flac; do ffmpeg -i "$f" -acodec alac "${f/.flac/}".m4a; done

it works great to encode all the files that are .flac to apples lossless with the m4a container.

is there a way for me to tell it to run on multiple threads so i can encode more files, faster?

pan64 · 05-19-2012, 09:03 AM

no, multithreading will not work, but you can try multitasking. To do this you need to add a & at the end of the command:
for f in *.flac; do ffmpeg .... &; done

lej · 05-20-2012, 02:04 AM

ffmpeg supports threads, see the -threads option. This is unlikely to provide a linear increase in performance, however. I would rather run one instance per cpu/core.

The problem with using a simple & is that you lose control over how many intances are started. Running more instances than you have cpus will slow things down. The shell doesn't have any builtin support for doing this, though there are ways to work around it.

Alternatively, you could always write a little Makefile and use make -j N. This will also have the advantage of skipping files that have already been encoded.

Code:

files:= $(patsubst %.flac,%.m4a,$(wildcard *.flac))

all: $(files)

%.m4a : %.flac
        @ffmpeg -i $< -acodec alac $@

edit: you need to make sure that the '@ffmpeg ...' line is indented with a tab, since the tab is expanded to spaces when posted/pasted.

lazardo · 05-21-2012, 09:17 PM

Versions > 8.10 are multi-threaded.

http://www.ffmpeg.org/

Cheers,

pan64 · 05-22-2012, 01:04 AM

actually ffmpeg itself may or may not be multithreaded, but it can process only one file. So based on the original post:

Quote:

is there a way for me to tell it to run on multiple threads so i can encode more files, faster

In general if you have several cores you can speed up the conversion by ffmpegs' internal multithreading. In case you want to convert several files this kind of multithreading will have no meaning because you can start all the conversions at the same time and they will surely eat up all your resources (this was described in my previous post).
As lej wrote you can write a simple makefile to control the number of instances, but using this together with multithreading will not give you the expected result.