Short and branched chain specific acyl-CoA dehydrogenase that catalyzes the proR-proR stereospecific alpha,beta-dehydrogenation of fatty acyl-CoA thioesters using the electron transfer flavoprotein (ETF) as their physiologic electron acceptor, resulting in the formation of trans-2-enoyl-CoA ((2E)-enoyl-CoA) (PubMed:10832746, PubMed:11013134, PubMed:21430231, PubMed:7698750). Among the different mitochondrial acyl-CoA dehydrogenases, acts specifically on short and branched chain acyl-CoA derivatives such as (S)-2-methylbutyryl-CoA as well as short straight chain acyl-CoAs such as butyryl-CoA (butanoyl- CoA) (PubMed:10832746, PubMed:11013134, PubMed:21430231, PubMed:7698750). Plays an important role in the metabolism of L- isoleucine by catalyzing the dehydrogenation of 2-methylbutyryl-CoA, one of the steps of the L-isoleucine catabolic pathway (PubMed:10832746, PubMed:11013134). Can also act on valproyl-CoA, a metabolite of valproic acid, an antiepileptic drug (PubMed:8660691). {ECO:0000269|PubMed:10832746, ECO:0000269|PubMed:11013134, ECO:0000269|PubMed:21430231, ECO:0000269|PubMed:7698750, ECO:0000269|PubMed:8660691}. This is the function of ACADSB (acyl-CoA dehydrogenase short/branched chain, Ensembl gene identifier ENSG00000196177).