This is a “vocalise”, a wordless piece designed to exercise the player’s “singing style”. You know the famous “Trololol” meme? That’s a vocalise — in fact, the last word on the title card is “Vocalise” in Russian.
This particular one is by Marco Bordogni, who wrote a lot of them. In the 1920s, Joannès Rochut collected and edited them, publishing them as “Melodious Études for Trombone”. It’s a standard of the literature: Most high-school classical trombonists have played some before they graduate. (Here’s the sheet music.)
The series of 120 is arranged progressively, (arguably) from easiest to hardest. This is No. 16, so still fairly “easy”, as they go. Recorded without any cuts or effects. Enjoy!