Blender multithreaded rendering

Makefile

CHROMASTART=0
CHROMAEND=0

MAINSTART=0
MAINEND=0
NJOBS=8

BATCH=$$(( ($(END) - $(START)) / $(NJOBS) ))
LAST=$$(( $(NJOBS)-1 ))
BLENDFILES=$(wildcard *.blend)

RULES=$(shell seq 0 $(LAST))
CHROMARULES=$(addprefix render/chroma, $(addsuffix .mkv, $(RULES)))
MAINRULES=$(addprefix render/main, $(addsuffix .mkv, $(RULES)))

default:
        @echo "Use render/chroma.mkv or youtube.mkv rules."

clean:
        rm -Rf source/BL_proxy render/*

upload: youtube.mkv thumb.png
        youtube-upload --privacy=private --thumbnail=thumb.png --title=youtube.mkv youtube.mkv

reupload:
        youtube-upload --privacy=private --thumbnail=thumb.png --title=youtube.mkv youtube.mkv

render/chroma.txt: Makefile
        truncate -s 0 $@
        for f in $(notdir $(CHROMARULES)); do echo "file '$$f'" >> $@; done

render/main.txt: Makefile
        truncate -s 0 $@
        for f in $(notdir $(MAINRULES)); do echo "file '$$f'" >> $@; done

render/chroma.mkv: render/chroma.txt $(CHROMARULES)
        nice ffmpeg -y -f concat -i $< -c:v copy -f matroska $@
        rm -f $(CHROMARULES)

youtube.mkv: render/main.txt $(MAINRULES) render/session.flac
        nice ffmpeg -y -f concat -i render/main.txt -i render/session.flac -map 0:0 -map 1:0 -c:v libx264 -preset medium -crf 18 -c:a copy -f matroska $@

render/chroma%.mkv: $(BLENDFILES)
        ./renderpart "Chroma Key" $(NJOBS) $@ $(CHROMASTART) $(CHROMAEND)

render/main%.mkv: $(BLENDFILES)
        ./renderpart "Video Edits" $(NJOBS) $@ $(MAINSTART) $(MAINEND)

.PHONY: default clean upload reupload

renderpart

#!/usr/bin/env php
<?php

list($me, $scene, $njobs, $output, $start, $end) = $argv;

if($end == 0) die(1);

preg_match('%(?<i>[0-9+])([^0-9]*)$%', $output, $match);
$i = (int)$match['i'];
$len = floor(((float)$end - (float)$start) / (float)$njobs);
$last = (int)((int)$njobs - 1);

$command = sprintf(
	'nice blender -noaudio -b %s -S %s -o %s -x 0 -s %d -e %d -a | grep Saving',
	escapeshellarg(substr(shell_exec('find . -maxdepth 1 -name "*.blend" | head -n 1'), 0, -1)),
	escapeshellarg($scene),
	escapeshellarg($output),
	$i === 0 ? $start : ($start + $i*$len+1),
	$i === $last ? $end : ($start + ($i+1)*$len)
);

echo $command."\n";
passthru($command, $r);
die($r);

You should use nproc(1) to determine how many processes to run at once.