This video contains English subtitles put in by MEMRI TV (Middle East Media Research Institute). Memri is an Israeli Zionist propaganda organization that whitewashes Israeli war crimes by misinforming the public with intentional mistranslations of speeches in Arabic. They were caught countless times giving different meaning to the words of Iranian and Palestinian public figures to keep the Muslim sentiment alive. This video however is of little significance, as its sole purpose is to foster the negative image of Muslims, whether they support ISIS or not, which means that in this case it would make little sense for MEMRI to intentionally mistranslate.
The video alleges to depict a public execution of an alleged infidel by ISIS militants in Mosul. The victim is shot in the back of his head at point blank range. There appears to be at least one child in the crowd.
The video also contains a little bit of footage of soldiers captured by ISIS at Camp Speicher.