The Telegram iOS app plays videos with stereo audio as mono, with the left and right channels being identical. The same video plays correctly in stereo in Telegram Web and after being saved to the device and played in another player.
The issue is reproducible with both wired and Bluetooth headphones. It has also been reproduced on iPad Air (6th gen) and previously on iPhone 14 Pro Max. Reinstalling the app does not resolve the issue, and a third-party iOS Telegram client shows the same behavior.
Steps to reproduce
Open the Telegram iOS app and go to any chat or channel containing a video with stereo audio.
Connect headphones, either wired or Bluetooth, and play the video in the app.
Listen to the left and right audio channels: both channels play identical audio.
For comparison, play the same video in Telegram Web, or save it to Photos and play it there.
Current result
The video audio is played as mono in the Telegram iOS app: the left and right channels are identical.
Expected result
The video should play with its original stereo audio, with distinct left and right channels, as it does in Telegram Web and when the saved video file is played in another player.
The same issue also occurs on iPhone 15 Pro Max running iOS 27.0.1 and Telegram version 13.0. Videos only play in mono when viewed directly in Telegram, but stereo audio works correctly after downloading the videos to the device.