How I Built a Telegram Video Avatar Bot With Python and FFmpeg

I tried to set a video avatar on Telegram last month. Recorded a short clip on my iPhone, uploaded it, and nothing happened. No error message. No toast notification. Telegram just silently rejected it. Turns out iPhone records in HEVC (H.265) by default since the iPhone 7. Telegram's video avatar system only accepts H.264. When you upload HEVC, the server validates it, fails, and tells you absolutely nothing. I spent two hours thinking my internet connection was broken before I figured this out.