Validity of visa before stamping

Subject to the border re-opening, they are closed unit May 31 and can be extended, yes you can travel in August.
At the airport you will need proof of funds, return ticket and confirmed hotel reservation for the maximum 90 days.

It's unlikely that any visas will be issued until Brazil begins admitting foreigners again, so you probably will not be able to obtain a visa very far in advance of your intended trip. 

Unlike some countries, Brazilian visas generally do not specify a "first use by" date, so the authorities are reasonably liberal on travel times.  You've said in another thread that you'll be applying for a student visa, which is a VITEM IV.  To obtain a VITEM IV, you'll need to present, among other documents, a travel itinerary to and from Brazil (from an airline or a travel agent), and an acceptance document from a Brazilian educational institution.  Your visa will be granted with your travel dates and your class start dates in mind, so you'll ordinarily be expected to travel on or near those dates.

Remember, as stated elsewhere, a visa only gives you the ability to GO to Brazil, not the right to STAY in Brazil:  you need to obtain that from the Federal Police, within 30 days of your arrival.  The Federal Police will scrutinize the acceptance document from the Brazilian educational institution, and if your arrival date is significantly later than the course dates indicated, you'll need to provide an explanation, and probably a revised acceptance document, as well.  They will also expect your police reports from your country of origin to be no more than 90 days old, so if the time between your visa application abroad and your application for residency authorization to the Federal Police is longer than that, you should obtain a fresh set of police reports before leaving for Brazil.  The Federal Police process is totally separate from the visa process, and the Federal Police will make the final decision, based on your interview and the documents you present,  on whether you can stay in Brazil or need to leave.

Thanks for reply. University issue me the letter for joining me on 1st july but I am bit worried if Covid-19 issue not resolve than I may need to extend this. Yes there also a possibility that Brazilian Embassy will not issue me the visa due to Covid-19.

That is all up to the Brazilian Embassy's/Consulates. The Consulates in BR are working on emergency only issues. DPF is not working on any  extensions migration issue under to same emergency orders.
Not sure if any schools will be open.
Basically recommend checking all Gov. and your school websites .