My iPhone clip uploaded fine. Telegram showed the spinner, then quietly kept my old photo. No error, no toast, nothing in the logs. I re-recorded the clip twice before realizing the upload wasn't failing, it was being silently discarded.
The reason: iPhones have recorded HEVC (H.265) by default since iOS 11, and Telegram's video avatar pipeline only accepts H.264. Wrong codec means the client drops your file without a word. I lost an evening to this, then built a bot so I'd never have to debug it again.
What Telegram actually wants
The video avatar requirements aren't written down in one place. I pieced them together from the limits page, the Bot API docs, and a pile of trial uploads:
Codec: H.264. HEVC gets silently rejected.
