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Estimate the size of each video
- Convert the duration to seconds. For example, 10 minutes is 600 seconds; 1 hour, 2 minutes, and 30 seconds is 3,750 seconds.
- Choose the export assumptions. Identify the resolution, frame-rate class, and whether the video is SDR or HDR. Use a video bitrate appropriate to those settings.
- Add the audio bitrate. The calculation needs the combined audio and video bitrate, not video bitrate alone.
- Multiply duration by combined bitrate, then divide by eight. The result is an approximate number of bytes.
- Repeat for every video and add the results. If every video uses the same bitrate assumption, you can add the durations first and calculate once.
YouTube’s Data API describes duration and uploaded bitrate as separate video properties, reflecting why duration alone cannot determine file size (YouTube Data API: Videos). For upload handling, the YouTube Data API’s resumable-upload documentation uses the video file’s byte size as the content length (Resumable Uploads).
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Choose a bitrate assumption
YouTube recommends MP4 with H.264 video, matching the frame rate used during recording, and variable bitrate (VBR). Its published rates are references for upload encoding—not guaranteed output sizes. The table shows YouTube’s SDR video bitrate recommendations; add the applicable audio rate separately. Check the current YouTube recommended upload encoding settings before encoding, since recommendations may change.
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|---|---|---|
| 720p | 5 Mbps | 7.5 Mbps |
| 1080p | 8 Mbps | 12 Mbps |
| 2160p (4K) | 35–45 Mbps | 53–68 Mbps |
For audio, YouTube’s references are 384 kbps for stereo, 128 kbps for mono, and 512 kbps for 5.1. HDR recommendations are higher than SDR for the same resolution class; consult YouTube’s current table for those rates rather than applying the SDR figures.
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Worked example: 10 minutes at 1080p, 30 fps
Using YouTube’s 8 Mbps SDR video reference for standard frame rates and 384 kbps for stereo audio gives a combined assumption of 8.384 Mbps, or 8,384,000 bits per second. For 600 seconds: 8,384,000 × 600 ÷ 8 = 628,800,000 bytes. That is about 629 MB using decimal units (1 MB = 1,000,000 bytes), or about 600 MiB using binary units (1 MiB = 1,048,576 bytes). This is arithmetic from YouTube’s reference rates, not a measured encode or an exact file-size promise.
Estimate a playlist without mixing unlike exports
For a playlist with varied clips, calculate each video separately using its own duration and export assumptions. A 4K HDR clip at 60 fps should not be estimated using the same 1080p30 assumption as another item in the playlist. Add the resulting byte estimates, then convert the total into decimal GB (1 GB = 1,000,000,000 bytes) or binary GiB (1 GiB = 1,073,741,824 bytes), labeling which unit you use.
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If you do not yet know the encoder’s average bitrate, make a lower and upper estimate using a bitrate range while holding the duration and other settings constant. This shows how much the assumption affects the storage plan without suggesting a universal safety margin.
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- VBR and quality-targeted encoding: A bitrate reference is an assumption, not a fixed rate. In variable-bitrate or constrained-quality workflows, the encoder can allocate different amounts of data across scenes.
- Motion and detail: Content affects bit allocation in quality-targeted encoding. Google’s VP9 guidance describes allocating more bits to difficult scenes and fewer to easier ones; that illustrates content dependence, not an H.264 recommendation for YouTube MP4 uploads (Google Media: VP9 Encoding Recommendations).
- Resolution, frame rate, and HDR: YouTube’s recommended reference rates differ across these classes, so use assumptions that match each export.
- Audio: Omitting audio understates the estimate; use the rate for the intended channel layout.
- Container overhead and metadata: The simple bitrate formula does not account for every stream, container, or metadata detail.
Common estimation mistakes
- Using duration alone: Two clips with equal durations can have different sizes if their combined average bitrates differ.
- Dividing by eight twice—or not at all: Bitrate is in bits per second; dividing the product by eight converts bits to bytes.
- Mixing Mbps and kbps: Convert to a consistent unit before adding audio and video. For example, 384 kbps is 0.384 Mbps.
- Confusing MB with MiB: State whether the result uses decimal or binary units; the labels are not interchangeable.
- Treating YouTube’s recommendation as a guaranteed encoder output: It is a planning reference. Actual size depends on the export’s average bitrate and other encoding details.
When the playlist is meant to run as a YouTube livestream
File-size estimates help plan storage for uploaded recordings, but they do not calculate livestream bandwidth or guarantee a particular livestream outcome. If the goal is to keep uploaded videos playing as a YouTube livestream, StreamNeo runs the playlist from the cloud, so your computer does not have to stay on. Upload the videos, add your YouTube stream key, and go live. It loops uploaded videos, with one flat price per slot for any quality up to 4K 60fps as uploaded, and automatic recovery if YouTube drops the stream. The first day is free with no card. Monthly: $9.99 per month. Start your free day with StreamNeo.
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