Video Bitrate & Storage Calculator – FFmpeg Command Generator
Video Transcoding & Output Settings
Bandwidth, Storage & CDN Budget
Understanding Video Bitrate, Codecs & Storage Budgets
Video bitrate represents the number of data bits processed per unit of time (measured in kbps or Mbps). Balancing bitrate against video resolution, frame rate, and compression efficiency is critical for maintaining pristine visual quality while preventing playback buffering and runaway CDN egress bills.
Codec Comparison: H.264 vs H.265 vs AV1
- H.264 (AVC): The universal standard. Compatible with virtually 100% of browsers, legacy televisions, iOS, and Android devices. Requires approximately 6,000 kbps for clean 1080p 30fps video.
- H.265 (HEVC): Offers roughly 35% to 40% bandwidth savings over H.264 at identical perceptual quality. Ideal for 4K UHD streaming, Apple ecosystem distribution, and high-efficiency archival.
- AV1: The modern open-source, royalty-free codec backed by Google, Netflix, and Amazon. Delivers up to 50% greater compression efficiency than H.264, making 4K and 8K streaming accessible on modern browsers.
Why Does Upload Speed Need a 1.5× Safety Margin?
When broadcasting live video via RTMP or SRT (OBS Studio, vMix, Wirecast), fluctuating cellular or cable ISP throughput causes instantaneous bitrate spikes. Configuring your broadcast encoder with an upload margin of at least 1.5× to 2.0× above your target stream bitrate prevents packet loss and frame drops.
Frequently asked questions
What formula calculates video file size from bitrate?
File size is calculated as: Size (Megabytes) = (Total Bitrate in kbps × Duration in seconds) ÷ (8 × 1024). For example, a 10-minute video at 6,192 kbps total bitrate produces approximately 453 MB.
What is the faststart flag in FFmpeg?
The flag '-movflags +faststart' moves the MP4 metadata index (moov atom) from the end of the file to the beginning. This allows browsers to start instant progressive playback without downloading the entire video first.
When should I choose 2-Pass encoding?
2-Pass encoding scans the entire video during the first pass to identify complex, fast-motion scenes, then dynamically allocates more bitrate where needed during the second pass. It produces optimal quality for fixed file size budgets.
How does frame rate affect required bitrate?
Going from 30 fps to 60 fps increases the temporal information by 100%. Modern inter-frame compression leverages motion vectors, so you generally need a 40% to 50% bitrate increase rather than a full 2× increase to maintain quality.