The Android app may fail to send certain videos (most often, when they were downloaded from other apps) if you try sharing them by tapping the Paperclip Icon > Gallery. The video will fail to send, and a red exclamation mark will appear next to it in the chat.
This happens due to a failure in the MediaCodec Android component, and is not an issue of the Telegram Android app.
Open the Gallery App on your device > open the video > Share it with Telegram. Alternatively, you can send the video without compression, using Paperclip Icon > File.