ビデオビットレート計算機

Each generation of video codec achieves better compression at equivalent quality. AV1 requires roughly 50% the bitrate of H.264 for equivalent visual quality, H.265/HEVC about 40–50% less than H.264, and VP9 about 30–40% less. This means a 1080p stream that needs 8 Mbps in H.264 might need only 4 Mbps in H.265 or 3 Mbps in AV1. The trade-off is encoding complexity: AV1 encodes much slower than H.264 and requires more capable hardware decoders.

CBR (Constant Bitrate) maintains a fixed bitrate throughout the video, which is predictable for streaming but wastes bits on simple scenes. VBR (Variable Bitrate) allocates more bits to complex scenes (fast motion, detail) and fewer to simple scenes, achieving better quality at the same average bitrate. CRF (Constant Rate Factor) is a quality-based mode where the encoder targets a perceptual quality level and lets the bitrate vary as needed — preferred for offline encoding where file size is less critical than quality.

Higher frame rates require more bits because each additional frame contains new information that must be encoded. However, the relationship is not linear: H.264 and H.265 use temporal prediction (B-frames and P-frames) that references nearby frames, so 60fps at double the frame rate typically requires only about 60–75% more bitrate than 30fps, not double. High frame rates also improve motion clarity, which benefits fast-paced content like sports and gaming.

YouTube recommends for 1080p at 30fps: 8 Mbps for H.264, or 5 Mbps with VP9/AV1. For 4K at 30fps: 35–45 Mbps H.264 or 15–20 Mbps VP9/AV1. Twitch recommends 6 Mbps maximum for 1080p60. Netflix encodes at multiple bitrates (300 Kbps to 16+ Mbps) and delivers the appropriate quality based on viewer bandwidth. Platform-specific recommendations account for re-encoding: always upload at the highest quality your bandwidth allows.