FAQ) Why won't VEGAS open my file correctly? Codecs, Converters etc.
How To Fix MP4/AVI File Import Error on Sony Vegas Pro - How to Batch Convert Videos Using HandBrake - YouTube
Cannot open .mp4 files on Sony Vegas 13? : r/VideoEditing
Como solucionar el error de Sony Vegas al abrir video MP4. (Versiones 13, 12, 11, 10 y 9)
Have recently been getting this issue with VEGAS 16 where i cant import any of my mp4 files. The codec for the video file is: MPEG-4 AVC. Any help? : r/ VegasPro
Problem occurred when Vegas open mp4 files? - Techyv.com