Bitrate

Bitrate (or bit rate) is the fundamental unit of data throughput. In networking it measures how fast data moves across a link. In media encoding it measures how much data represents one second of audio or video. Both use the same unit — bits per second — but describe different things: one is about transport, the other about quality.

Bitrate vs bandwidth vs throughput

Bandwidth is the maximum capacity of a link — the theoretical ceiling set by the physical medium and protocol. A 1 Gbps Ethernet port has 1 Gbps of bandwidth. Throughput is the actual data rate achieved under real conditions, accounting for protocol overhead, retransmissions, and congestion — typically 85–95% of bandwidth on a healthy connection. Bitrate in the media context refers to the data rate at which a specific stream is encoded or transmitted, which must stay within the available throughput. When your ISP advertises "100 Mbps," that is the bandwidth. What your speed test measures is throughput. What Netflix requires is a minimum sustained bitrate.

CBR vs VBR

Constant Bitrate (CBR) encoding produces a fixed number of bits per second regardless of scene complexity. Simple static scenes waste bits; complex action scenes may look blocky. CBR is used where a predictable, fixed bandwidth allocation is required — live streaming to Twitch, broadcasting over fixed-bandwidth links, or burning video to disc. Variable Bitrate (VBR) allocates more bits to complex scenes and fewer to simple ones, producing better quality at the same average bitrate. VBR is standard for stored video (Netflix, YouTube VOD, Blu-ray). A VBR file might have an average bitrate of 8 Mbps but peak to 40 Mbps during a fast-action scene — your connection's sustained throughput must handle the peaks.

Video codec efficiency: H.264 vs H.265

Codec choice dramatically affects how much bitrate a given quality level requires. H.265 (HEVC) achieves roughly the same visual quality as H.264 at half the bitrate — a 1080p stream that needs 8 Mbps in H.264 needs only 4 Mbps in H.265. AV1, an open royalty-free codec, matches or exceeds H.265 efficiency and is now widely used by YouTube and Netflix for 4K delivery. The trade-off is encoding complexity: H.265 and AV1 require significantly more CPU or GPU to encode and decode, which is why older devices may struggle with high-bitrate H.265 streams.

Streaming platform bitrates

Audio bitrate

Audio requires far less bitrate than video. MP3 at 320 kbps is transparent to most listeners. AAC achieves similar quality at 256 kbps. FLAC and ALAC are lossless formats — a 44.1 kHz stereo FLAC file uses roughly 1,000–1,400 kbps (1–1.4 Mbps). For podcasts and voice calls, 64–96 kbps AAC or Opus is sufficient. Streaming services cap audio at 320 kbps lossy or offer lossless tiers; the difference in required connection speed is negligible compared to video.

Live streaming encoding bitrate

For live streaming to Twitch or YouTube via OBS or similar software, the upload bitrate you configure in the encoder is the sustained upload load your connection must support continuously. Twitch recommends 6,000 kbps (6 Mbps) for 1080p60 using H.264. YouTube Live supports up to 51 Mbps for 4K60. The key difference from VOD is that live encoding uses CBR — the bitrate is fixed and must never exceed what your upload connection can sustain, or the stream will drop frames and rebuffer for viewers. Set your encoder bitrate to no more than 80% of your measured upload speed to leave headroom for other traffic and network variability.

Checking bitrate during playback

On YouTube, right-click the video and select "Stats for nerds" — this shows the current resolution, codec, and connection speed (the bitrate being delivered). On Netflix, use the keyboard shortcut Ctrl+Shift+Alt+D (Windows) or Ctrl+Shift+Alt+S to show a diagnostics overlay including current bitrate and selected quality tier. In VLC, use Tools → Media Information → Statistics for real-time bitrate graphs of local files.

Bitrate to file size conversion

File size = bitrate × duration ÷ 8 (to convert bits to bytes). A 2-hour movie encoded at 10 Mbps = 10,000,000 × 7,200 ÷ 8 = 9,000,000,000 bytes = approximately 9 GB. A 1-hour podcast at 128 kbps = 128,000 × 3,600 ÷ 8 = 57,600,000 bytes = approximately 55 MB. This math is useful for estimating storage requirements and data usage for offline downloads.

Frequently Asked Questions

What is the difference between bitrate and bandwidth?

Bandwidth is the maximum capacity of a link — the theoretical ceiling. Bitrate is the actual data rate at a given moment. A 100 Mbps connection might deliver 80 Mbps of real throughput under typical conditions.

What bitrate do I need to stream 4K video?

Netflix 4K uses 15–25 Mbps; YouTube 4K uses 20–45 Mbps; Disney+ 4K uses around 25 Mbps. Add headroom for other devices sharing the connection.

Why does video quality drop during playback?

Streaming services use adaptive bitrate (ABR) — the player monitors available bandwidth and drops to a lower-quality tier when throughput falls. A sudden drop from 1080p to 720p means your connection bitrate fell below the threshold for the higher tier.