Bjørn H Jespersen of the excellent .processing blog assisted greatly in identifying this as a BETAB-500M62 free-fall 500kg bomb, primarily used to attack concrete and hardened structures, as seen here [source]
According to Jane's the "bombs are believed to be cleared for carriage on MiG-21 'Fishbed', MiG-27 'Flogger', MiG-29 'Fulcrum', Su-22 'Fitter', Su-24 'Fencer', Su-25 'Frogfoot', Su-27 'Flanker', Tu-95 'Bear', Tu-16 'Badger', Tu-22 'Blinder' and Tu-22M 'Backfire'", which includes the aircraft used by the Syrian Air Force.
Update September 19th The second half of this video shows the same BETAB as filmed above
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