Source: https://guthlabs.ai/docs/instruments/video-bitrate-file-size-calculator/mechanism/

instrument mechanism / verified-clean

# Video Bitrate / File Size Calculator mechanism

The inspectable method record for Video Bitrate / File Size Calculator, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The arithmetic formulas are standard under the stated decimal-unit assumptions, but the spec needs review because it ambiguously defines audio bitrate handling and file-size units. The honest-label wording is directionally appropriate but should also disclose container and metadata overhead.

- The size formula is correct only when bitrate is the total stream bitrate in decimal Mbps and the result is decimal megabytes (MB).

- The specification lists an audio track bitrate but does not define whether the supplied bitrate already includes audio or whether audio bitrate must be added to video bitrate.

- The inverse formula is correct for required total bitrate, but it does not state whether the result is video-only bitrate or total video-plus-audio bitrate.

- The formulas omit container overhead, headers, metadata, and other non-media data; the honest label mentions codec/VBR variation but does not explicitly mention container overhead.

## Units and conventions

- 1 Mbps means 1,000,000 bits per second.

- 1 MB means 1,000,000 bytes; the formulas do not produce MiB unless a conversion is applied.

- Duration is measured in seconds.

- Bitrate values are measured in Mbps.

- For vectors using separate video and audio bitrates, total bitrate is assumed to be video bitrate plus audio bitrate.

- Required bitrate assumes the target size is a decimal MB value unless explicitly converted from MiB.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "duration_s": 600,
    "bitrate_mbps": 8
  },
  "expected_outputs": {
    "file_size_MB": 600
  },
  "working": "size = bitrate × duration ÷ 8\n= 8 Mbps × 600 s ÷ 8\n= 4,800 ÷ 8\n= 600 MB"
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

A zero-duration inverse calculation produces an undefined result and must be rejected. The specification also leaves audio-bitrate inclusion and decimal-versus-binary size units ambiguous, which can produce materially different displayed results.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/video-bitrate-file-size-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/video-bitrate-file-size-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/video-bitrate-file-size-calculator/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`