How big is a 3-minute Short at YouTube's 8 Mbps? About 189 MB

A 3-minute Short at YouTube's recommended 1080p rate of 8 Mbps is 180 MB of video, plus about 8.6 MB of 384 kbps stereo audio: roughly 189 MB. That figure is arithmetic on YouTube's example bitrates, not a limit. Sume's video inspect returns size_bytes and duration_seconds, so you can compute your own file's average rate with one division and compare it with the examples.

The numbers YouTube gives

YouTube Help: Recommended upload encoding settings, read 2026-10-04, lists example SDR bitrates of 8 Mbps at 1080p, 5 Mbps at 720p and 35 to 45 Mbps at 4K, with stereo audio at 384 kbps. The Shorts requirements page, YouTube Shorts requirements, says Shorts can be uploaded at a maximum of 1080p, so the 4K row does not apply to a Short.

The formula and the check

Size in megabytes is rate in Mbps times seconds divided by 8. Audio at 384 kbps over 180 seconds adds 0.384 x 180 / 8 = 8.64 MB. Going the other way, average rate is size_bytes x 8 / duration_seconds. Video inspect returns both fields in probe, each nullable, so guard for None.

def avg_mbps(size_bytes, duration_seconds):
    if not size_bytes or not duration_seconds:
        return None
    return size_bytes * 8 / duration_seconds / 1_000_000

print(round(avg_mbps(188_640_000, 180), 2))  # 8.38

TikTok ad caps change the answer

For a non-Spark TikTok in-feed ad, the TikTok Ads Help page, read 2026-10-04, lists up to 10 minutes, a file size at or under 500 MB, and a bitrate of at least 516 kbps. At 8.384 Mbps total, 500 MB lasts 4,000 Mb / 8.384 Mbps, about 477 seconds, so a 10-minute file at that rate (about 629 MB) is over the cap. At the 516 kbps floor, 600 seconds is 38.7 MB.

Sume cannot set a bitrate: encode keys such as crf and codec are refused with ffmpeg_fields_rejected. What you can control is length and geometry. Video trim shortens a clip, and its output option conforms width, height and fps on exact trims. If the probe says you are over a cap, cut the length.