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Bitrate to File Sizeの包括的な教育ガイドを準備中です。ステップバイステップの解説、数式、実例、専門家のヒントをお届けしますので、もうしばらくお待ちください。
The Bitrate to File Size Converter estimates final file size from video or audio bitrate × duration. Formula: File Size (MB) = (Bitrate × Duration × 60) ÷ 8 ÷ 1024 ÷ 1024. The division by 8 converts bits to bytes; the two divisions by 1024 convert to megabytes. Essential for streaming planning, video upload preparation, storage management, and bandwidth budgeting. Most users underestimate storage requirements until running out of disk space during a 4K project or streaming budget. Common bitrates by quality tier: **Audio:** AAC 128 kbps (Spotify standard) = 1 MB/min, AAC 320 kbps (high quality streaming) = 2.4 MB/min, FLAC ~1000 kbps lossless = 7.5 MB/min, uncompressed WAV 1411 kbps CD quality = 10.6 MB/min, 96 kHz hi-res 4608 kbps = 34.5 MB/min. **Video:** 720p YouTube 5 Mbps = 38 MB/min, 1080p YouTube 8 Mbps = 60 MB/min, 1080p Blu-ray quality 25 Mbps = 188 MB/min, 4K Netflix 15-25 Mbps = 112-188 MB/min, 4K HDR YouTube 35 Mbps = 263 MB/min, 4K ProRes editing 800 Mbps = 6 GB/min, 8K production 1500+ Mbps = 11 GB/min. Compression context: modern codecs (H.265/HEVC, AV1) achieve 30–50% better compression than older H.264 at same visual quality. Streaming services (Netflix, YouTube, Twitch) use sophisticated per-title bitrate optimization — same visual quality can be achieved at different bitrates depending on content complexity (animation vs live-action, fast vs slow motion). The headline 'Bitrate' in this calculator represents the encoder's setting; actual file size will match closely for constant bitrate (CBR) encoding, but variable bitrate (VBR) encoding produces somewhat different real sizes (lower if scene complexity averages lower than target). Use cases: Twitch streamers checking if their internet upload can sustain target bitrate; YouTubers estimating upload time and storage; video editors planning project storage; podcast producers calculating hosting costs; archivists planning media preservation storage. For streaming: required upload bandwidth in Mbps = stream bitrate in Mbps + 20% overhead headroom. A 6 Mbps stream needs 7.2+ Mbps actual upload capability sustained.
- 1Step 1 — Enter bitrate (in Mbps for video, Kbps usually for audio)
- 2Step 2 — Select unit (Mbps or Kbps to match input)
- 3Step 3 — Enter content duration in minutes
- 4Step 4 — Calculator converts bitrate to bytes per second (divide by 8)
- 5Step 5 — Multiplies by duration × 60 for total bytes
- 6Step 6 — Converts to MB (÷ 1024 × 1024) and GB (÷ 1024) for display
- 7Step 7 — Output displays both MB and GB for different scale comparisons
10 Mbps × 60 min × 60 sec ÷ 8 = 4500 MB. Standard 1080p file size — fits roughly on a DVD.
Standard podcast hosting size
Most podcast hosts charge per GB of bandwidth used; 60-min episode at 128 kbps is the audio sweet spot.
4K streaming bitrate × 2-hour movie. Why Netflix recommends 25 Mbps internet for 4K — that's the streaming bandwidth, not file size.
8K editing requires substantial storage — RAID arrays or fast network storage essential
Production raw bitrates dramatically higher than streaming. Local editing of 8K demands serious infrastructure.
Streaming bandwidth budgeting (Twitch, YouTube Live)
Video upload time estimation
Storage capacity planning for editing projects
Podcast hosting cost calculation
Archival storage requirements
Bandwidth budgeting for video conferencing
What bitrate do I need for streaming on Twitch?
Twitch limits streamers to 6 Mbps bitrate for non-partners (8 Mbps for partners). Setting: 1080p 60fps = 6000 kbps, 1080p 30fps = 4500 kbps, 720p 60fps = 4500 kbps. Upload bandwidth needed = bitrate × 1.2 (20% headroom). Required upload: 7.5 Mbps for 1080p 60. Use speedtest.net to verify your real upload speed before configuring stream.
Why do streaming services use different bitrates than the same content I download?
Streaming uses adaptive bitrate — your player switches between multiple quality versions based on internet speed. Each version is encoded separately. Netflix 1080p high might be 5 Mbps; 4K 15-25 Mbps. Same content downloaded for offline viewing uses different bitrate again. The number you see in the calculator is the encoder setting, not necessarily what gets delivered to your screen.
Is higher bitrate always better quality?
Not always. Newer codecs (H.265/HEVC, AV1) achieve same visual quality at 30–50% lower bitrate than H.264. A 5 Mbps H.265 stream can look better than 8 Mbps H.264. Content type matters: animation needs less bitrate than live-action, slow scenes need less than fast action. Modern streaming services optimize per-title. For uploads, use modern codec at appropriate bitrate rather than maximum bitrate at outdated codec.
How does this differ from internet bandwidth requirements?
Bitrate = data rate of the file itself. Bandwidth requirement = bitrate + protocol overhead (~10–20%) + headroom for variability. 6 Mbps stream needs roughly 7.5–8 Mbps reliable internet. For downloads, internet speed determines download time: 1 GB file at 100 Mbps internet downloads in 80 seconds; at 10 Mbps in 13 minutes.
What about lossless vs lossy compression for archival?
Lossless (FLAC for audio, ProRes/DNxHR for video, Apple ProRes RAW) preserves original data — no quality loss but file sizes 5–20× larger than lossy equivalents. Use lossless for: master copies, source files for editing, archival of irreplaceable content. Lossy (AAC, MP3, H.264, H.265) is fine for: final distribution, streaming, casual playback. Don't archive in lossy format — quality cannot be recovered if needed for re-edit later.
プロのヒント
Match your streaming bitrate to your upload bandwidth's 80% sustained capacity — if your internet provides 10 Mbps actual sustained upload (measured, not advertised), cap stream bitrate at 8 Mbps. Test sustained upload during peak hours, not just speed tests at quiet times.