HLS & DASH Segment Bitrate Calculator

Calculate streaming segment file size, player buffer duration, and CDN egress bandwidth per concurrent viewer cohort.

Stream Bitrates & Segment Parameters

Video Bitrate (kbps) e.g. 4500 kbps for 1080p60

Audio Bitrate (kbps) e.g. 128 kbps stereo AAC

Segment Target Duration (s) Apple RFC 8216 standard: 6s (or 2s for low-latency)

Container Format & Mux Overhead Container packaging headers

Concurrent Viewers Simultaneous active video sessions

Player Buffer Lookahead (chunks) Default HLS forward buffer: 3 chunks

HLS Segment Chunk Size

-- MB

Per .m4s / .ts chunk transferred by player

Player Buffer Duration

-- s

Buffer Memory Size

-- MB

Peak CDN Egress

-- Mbps

Egress per Viewer Hour

-- GB/hr

Est. Monthly Transfer (4h/day/viewer)

-- TB/mo

How HLS & DASH Segmentation and CDN Bandwidth Work

HTTP Live Streaming (RFC 8216) and MPEG-DASH deliver video by slicing compressed elementary video and audio streams into small, standalone HTTP files (segments or media fragments) referenced in an index playlist (.m3u8 or .mpd).

Primary Formulas

Segment File Size (MB):
Segment Size (MB) = [Total Bitrate (kbps) × Segment Duration (s)] / 8000
Where Total Bitrate incorporates video bitrate, audio bitrate, and container mux overhead (fMP4 CMAF ≈ 1.5%, MPEG-TS ≈ 8%).
CDN Egress Bandwidth (Mbps / Gbps):
Peak Egress (Mbps) = [Total Bitrate (kbps) × Concurrent Viewers] / 1000
Player Buffer Memory Window:
Buffer Duration (s) = Segment Duration (s) × Buffer Chunks Count
Standard HLS players keep a rolling window of 3 target segments in RAM to smooth over network fluctuations.

Frequently Asked Questions

What segment duration should I choose: 2s or 6s?

Apple HLS authoring guidelines historically specified 6-second segments for standard video on demand and live streaming to minimize HTTP request overhead and improve CDN caching efficiency. For Low-Latency HLS (LL-HLS) and interactive sports broadcasts, 2-second segments with CMAF chunked transfer are preferred.

Why does MPEG-TS have higher overhead than fragmented MP4 (fMP4)?

MPEG-2 Transport Stream (MPEG-TS) packets have fixed 188-byte sizes with repetitive 4-byte header prefixes and PES packetization overhead, creating 7% to 10% container bloat. Fragmented MP4 (CMAF ISO-BMFF) uses compact hierarchical box headers, reducing container overhead to roughly 1% to 2%.

How does concurrent viewer count affect CDN costs?

Unlike peer-to-peer or multicast, HLS is unicast HTTP delivery. Each concurrent viewer downloads individual segment chunks. Peak egress bandwidth determines ISP port commit requirements, while total monthly TB determines CDN egress billing charges.