sendVoice - mkotb/Telegram-Errors GitHub Wiki
Uh... this is an interesting one. No matter what file you provide, it will be shown to the client as a voice message. On Telegram Desktop, the file will be downloaded as an ogg file and if the default player in-app cannot open it, the client will open it in the default application for .ogg.
An XML file sent using this method with specified duration of 5 seconds