Contacting the nearest Vietnam embassy is the traditional way to apply for a visa to Vietnam
Typically, the visa application procedure at the embassies would require applicants to send off their original passport and fill application form (either in person or by mail). The normal waiting time for processing visa application is around 1 week (shorter time could be arranged for additional fee).
Because unlike applying for visa on arrival where you get a visa pre-approval letter in advance, then get the actual visa stamp at your arrival airport in Vietnam, when you apply for Vietnam visa through the embassy, the visa stamp will already be stamped onto your passport when the embassy send them back to you. That is the reason you need to send off your passport to the embassy, but not when applying for visa on arrival.
The application procedure as well as processing time may vary from one embassy to another. Therefore, if you want to apply for a visa to Vietnam through a Vietnam Embassy, you are highly recommended to contact the nearest embassy to where you are staying in advance to know the correct procedure and required documents to best prepare for your visa application and to save your time and cost as well.
No, you could apply for a visa at any Vietnam Embassy which is most convenient for you. However, as it might take up to several working days at least for the embassy to process your visa, and during that time you have to part with your passport, some might find it somewhat inconvenient. In this case, you could apply for visa on arrival as the process only takes two working days at most and you could apply from anywhere as long as you have access to the internet.
(*) For information of Vietnam embassies in foreign countries, including their addresses, phone numbers and email, please click on the relevant country on the list below.