When encoding video for streaming or physical media, balancing quality and file size is critical. This Video Rate Calculator helps you determine the exact bitrate required to fit a specific video duration into a target file size (like 700MB for a CD, 4.7GB for a DVD, or an upload limit).
The Formula:
The basic relationship between file size, duration, and bitrate is:
File Size = (Video Bitrate + Audio Bitrate) × Duration
Key Metrics Used:
Target File Size: The maximum space you have available (e.g., 50 MB for an email attachment or 4 GB for a USB drive).
Duration: The exact length of the video in hours, minutes, and seconds.
Audio Bitrate: Often overlooked, audio consumes a portion of your total bandwidth. Standard AAC audio is usually 128 kbps or 192 kbps. Subtracting this from the total allowed data rate gives you the remaining budget for video.
Overhead: File containers (like .mp4, .mkv, .avi) require a small amount of data for headers and indexing, typically 1% to 2% of the total file size.
Using this calculator ensures you maximize video quality without exceeding your storage or bandwidth limitations.
function calculateVideoBitrate() {
// 1. Get Inputs
var hours = parseFloat(document.getElementById('vrc_hours').value) || 0;
var minutes = parseFloat(document.getElementById('vrc_minutes').value) || 0;
var seconds = parseFloat(document.getElementById('vrc_seconds').value) || 0;
var targetSize = parseFloat(document.getElementById('vrc_size').value);
var sizeUnit = document.getElementById('vrc_size_unit').value;
var audioBitrate = parseFloat(document.getElementById('vrc_audio').value);
var overheadPercent = parseFloat(document.getElementById('vrc_overhead').value) || 0;
// 2. Validation
if (!targetSize || targetSize <= 0) {
alert("Please enter a valid target file size.");
return;
}
var totalSeconds = (hours * 3600) + (minutes * 60) + seconds;
if (totalSeconds total size
if (videoBitrateKbps <= 0) {
document.getElementById('vrc_result').style.display = 'block';
document.getElementById('res_vid_kbps').innerHTML = "Error";
document.getElementById('res_vid_mbps').innerHTML = "File size too small";
document.getElementById('res_total_kbps').innerText = totalBitrateKbps.toFixed(0) + " kbps";
document.getElementById('res_space_vid').innerText = "N/A";
document.getElementById('res_space_aud').innerText = "N/A";
return;
}
// Calculate Size Distribution for display
var audioTotalBits = audioBitrate * 1000 * totalSeconds; // bits
var videoTotalBits = videoBitrateKbps * 1000 * totalSeconds; // bits
// Convert back to MB for display
var audioSizeMB = (audioTotalBits / 8) / (1024 * 1024);
var videoSizeMB = (videoTotalBits / 8) / (1024 * 1024);
// 4. Output Results
document.getElementById('vrc_result').style.display = 'block';
document.getElementById('res_vid_kbps').innerText = Math.floor(videoBitrateKbps) + " kbps";
document.getElementById('res_vid_mbps').innerText = (videoBitrateKbps / 1000).toFixed(2) + " Mbps";
document.getElementById('res_total_kbps').innerText = Math.floor(totalBitrateKbps) + " kbps";
document.getElementById('res_space_vid').innerText = videoSizeMB.toFixed(1) + " MB";
document.getElementById('res_space_aud').innerText = audioSizeMB.toFixed(1) + " MB";
}