I would like to ask if there are best practices for choosing audio/video formats for websites to get the widest platform and browser support given limited resources especially in development time (for HTML coding, file format conversion, etc.).

I have Googled the answer without success (for example, there was vague or conflicting information) and I have also asked around but the answers I got were there are no best practices in this respect. If so, I would like to know if there has been any study or survey about how the majority of leading companies choose the audio/video formats for their websites.

Thank you very much for your help.