I found a reproducible issue in Telegram for Android that causes certain videos to be downloaded twice, resulting in approximately 2x the network traffic.
The issue specifically occurs with videos whose original message/file has been deleted after the video was sent, while a copy of the video still exists in Saved Messages or another chat.
Normal videos whose original file is still available do NOT have this problem.
Steps to reproduce
Send or receive a video in a Telegram chat.
Keep or forward a copy of the video to Saved Messages.
Delete the original video/message after it has been sent.
Open the saved copy and manually download the video.
Wait until the download reaches 100%.
At this point, the first download is completely finished. The video file is fully downloaded and can be played normally from beginning to end.
However, Telegram does NOT start the inline video preview/autoplay inside the chat.
By "inline video preview/autoplay", I mean the behavior where Telegram automatically plays the video silently inside the message without the user tapping on the video.
Without tapping, opening, or manually playing the video, Telegram starts downloading the same video again in the background.
The second download continues until approximately the entire size of the video has been downloaded again.
Only after the second download is completed does Telegram start the inline video preview/autoplay normally.
For example, with a 19 MB video:
First download: ~19 MB
Second download: ~19 MB
Total network traffic: ~38 MB
The important part is that the first 19 MB download is already complete and the video is fully playable before the second 19 MB download starts.
So, in practice, Telegram appears to download the video once for the actual playable video file, but then downloads the entire file again before it can use it for the inline video preview/autoplay.
Additional observations:
• The second download starts when the chat containing the video becomes visible.
• If I leave the chat, the second download stops.
• If I re-enter the chat, the second download starts again.
• There is no obvious download indicator in Telegram for this second download.
• Telegram's Storage Usage shows the "Miscellaneous" cache increasing by approximately the same size as the video during the second download.
• I verified the additional network traffic using NekoBox's traffic statistics.
• Video streaming is disabled; the issue still occurs.
• Automatic media download is disabled; the issue still occurs.
• Clearing Telegram's cache does not fix the issue.
• Reinstalling Telegram does not fix the issue.
• The issue has occurred across multiple Telegram Android versions, not only the current version.
⚠️ IMPORTANT DIFFERENCE:
This issue occurs in Telegram for Android, but does NOT occur in TurboTel 12.9.0 under the same conditions.
I tested the same type of video with the same Telegram account and the same network/proxy setup. TurboTel downloads the video only once and does not perform the additional full-size download when the chat is opened.
This suggests that the issue is likely related to Telegram Android's handling of the local video file and its inline preview/autoplay when the original Telegram file/message is no longer available, rather than being caused by the network connection or proxy.
Please investigate why Telegram Android cannot reuse the already downloaded video for the inline video preview/autoplay and instead downloads the entire video again.