Online messaging platforms, email providers, and forums impose hard file size attachment caps: Discord free tier limits uploads to 8MB, Gmail attachments cannot exceed 25MB, and Slack restricts single files to 100MB. This bitrate calculator computes the exact maximum combined video and audio bitrates needed to transcode a clip down to any specific megabyte threshold without exceeding destination limits.

### Target Bitrate Mathematical Formulas

Calculating required bitrates involves converting megabytes to bits and subtracting dedicated audio bandwidth: 1. **Target Budget in Kilobits ($1\text{ Byte} = 8\text{ bits}$):** $$\text{Total Budget (kilobits)} = \text{Target Size (MB)} \times 8 \times 1024$$ 2. **Audio Track Bandwidth Allocation:** $$\text{Audio Budget (kilobits)} = \text{Audio Bitrate (kbps)} \times \text{Duration (seconds)}$$ 3. **Available Video Track Bitrate ($R_{\text{video}}$):** $$R_{\text{video}} = \frac{\text{Total Budget} - \text{Audio Budget}}{\text{Duration (seconds)}}$$ 4. **Safety Margin (2% Container Overhead):** To account for MP4 container metadata (moov atom) and muxing variability, effective recommended video bitrate is reduced by 2%: $$R_{\text{recommended}} = R_{\text{video}} \times 0.98$$

### Worked Compression Example

Targeting an **8MB Discord upload** for a **90-second** video clip with a **128 kbps AAC audio track**: - **Total Budget:** $8 \times 8 \times 1024 = 65,536\text{ kilobits}$ - **Audio Allocation:** $128\text{ kbps} \times 90 = 11,520\text{ kilobits}$ - **Remaining Video Budget:** $65,536 - 11,520 = 54,016\text{ kilobits}$ - **Theoretical Video Bitrate:** $54,016 / 90 \approx 600.18\text{ kbps}$ - **Recommended Bitrate (with 2% margin):** $600.18 \times 0.98 \approx \mathbf{588\text{ kbps}}$ - Setting your encoder (FFmpeg, HandBrake, or Premiere Pro) to a video bitrate of 588 kbps guarantees the exported file lands just under the 8.0MB Discord barrier.

### In-Browser Calculation Guarantee

All bitrate equations and file limit calculations run locally in your web browser. No video clips or transcode parameters are stored or sent across the internet.