Audio File Size Estimator mechanism

Model scope

The formulas are standard under the stated assumptions, but the spec needs an explicit MB/GB convention, a clear distinction between raw PCM payload size and complete WAV file size, and required-input behavior when lossy bitrate is absent. The existing lossy honest label is appropriate but should also mention variable bitrate and container overhead.

• The PCM formula is correct for raw PCM payload bytes when sample rate is in samples/second, bit depth is in bits/sample, channels is a count, and duration is in seconds; it does not include WAV headers, metadata, padding, or other container overhead.
• The lossy formula is correct as a constant-bitrate estimate when bitrate is in bits/second, but it is not exact for variable-bitrate codecs and omits codec/container overhead.
• The output units MB/GB are ambiguous because the specification does not state whether they mean decimal MB/GB or binary MiB/GiB.

Units and conventions

• sampleRate is samples per second, such as 44100 or 48000 Hz.
• bitDepth is bits per sample per channel; dividing by 8 converts it to bytes per sample.
• channels is a dimensionless positive channel count.
• seconds is duration in seconds.
• bitrate is bits per second; a value such as 128 kbps must be converted to 128000 bits/second before applying the formula.
• Test outputs distinguish decimal MB (1 MB = 1000000 bytes) from binary MiB (1 MiB = 1048576 bytes).

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "mode": "PCM/WAV payload",
    "sample_rate_hz": 44100,
    "bit_depth_bits": 16,
    "channels": 2,
    "duration_seconds": 180
  },
  "expected_outputs": {
    "payload_bytes": 31752000,
    "payload_MB_decimal": 31.752,
    "payload_MiB": 30.2810668945
  },
  "working": "16 / 8 = 2 bytes/sample. 44100 samples/s × 2 bytes/sample × 2 channels = 176400 bytes/s. 176400 × 180 s = 31752000 bytes. 31752000 / 1000000 = 31.752 MB. 31752000 / 1048576 = 30.2810668945 MiB."
}

Failure boundary

• A lossy estimate cannot be computed when bitrate is omitted; the interface must require bitrate for lossy mode or clearly report missing input.
• Reject or clearly handle nonpositive sample rates, bit depths, channel counts, and negative durations; zero duration should produce zero bytes.
• Validate that bitrate is positive for lossy mode and that kbps-to-bits-per-second conversion is applied exactly once.
• Very long durations or large sample rates can exceed JavaScript safe integer precision if calculations are not guarded or performed with suitable numeric handling.
• A WAV file's actual size can exceed the PCM payload estimate because of headers, metadata, padding, and container structure.

Other records

Sources and evidence

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

• VERIFIED_LEDGER.json
• evidence-tranche3/tranche3-results.json