This great video must be around 15 years old. It's been on VHS for years and I guess they decided to upload it to YouTube. It starts off with good instruction about posture, breathing and holding the instrument. Then moves on to tonguing, phrasing, etc. There's a comical skit about the difference between a euphonium and baritone by Carlyle Weber (who is now retired and lives in S. Florida). Some excellent solo and ensemble playing too. It's almost 1:30 long but excellent!

Tuba & Euphonium: The Individual & The Ensemble

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Spoke with Carlyle Weber today (4-13). He told me they made that video in 1997 at Maryland's PBS TV station, so it was professionally done. He retired in 1998.