I have a few autographed DVDs and many more autographed CDs. None from conventions. I organized two small conventions and received autographed books from guest authors, and sketches and drawings (and one painting) from guest artists.

All of my autographed DVDs came from meeting either the artist of whom the documentary was about (like Jack Sheldon) or meeting the director or actors of the film (Chris Tashima, Jeff Adachi, etc.)

Most of my autographed CDs came from either buying them at performances by the artists or bringing the inserts to the performances. Some were trades by headliners for CDs signed by me and my band. I still have autographed LPs from decades ago (The LA Four, George Clinton, Pinchas Zukerman, etc.)

When I attended conventions, I sought out autographs and inscriptions in books they had written or edited. When I guest lectured at Comic Con, Russ Manning attended the lecture and traded me a few Tarzan colorkeys for my autograph in his con program. But I haven't attended a con in more than two decades... long before DVDs.