In Islam, does it permit a male a who is video recording himself at a gym that is not mixed of the opposite gender demonstrating certain exercises, while in the background there are males who are wearing shorts that are in the middle of the thigh or lower of the thigh and to upload them online for others to benefit from?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

It is not permissible to record or publish video clips that show the ‘Awrah or part of it, neither in the background nor in the picture itself.

The man's thigh is part of his 'Awrah (parts of the body that must be covered in Islam) according to the view of the majority of the scholars, because of the Hadeeth by ‘Abdur-Rahmaan ibn Jarhad, on the authority of his father who said: “The Prophet sat with us and my thigh was uncovered. He said: “Do you not know that the thigh is (part of the) ‘Awrah?” [Abu Daawood and others]

Moreover, the Fiqh Encyclopedia reads:

“The majority of jurists are of the view that the man's thigh is part of the 'Awrah and it must be covered, whether during the prayer or outside it.” [End of quote]

For more benefit, please refer to Fataawa 355957 and 88250.

Allah knows best.