Tibetan Buddhist canon
There is a long history of oral transmission of teachings in Tibetan Buddhism. Oral transmissions by lineage holders traditionally can take place in small groups or mass gatherings of listeners and may last for seconds (in the case of a mantra, for example) or months (as in the case of a section of the Tibetan Buddhist canon). It is held that a transmission can even occur without actually hearing, as in Asanga's visions of Maitreya.