Audio
Blu-ray's significant advantages over Audio CDs and DVDs are higher bitrates, better bit resolution for improved sound quality, and eight channels of surround sound for a more immersive audio experience. BD-ROM players are required to play three mandatory audio codecs, PCM, DTS, and Dolby Digital. And must use one of the mandatory codecs for the primary soundtrack for a movie, game or music album.
Each codec is unique and has its advantages and disadvantages. BDs can also play optional audio codecs like Dolby Atmos, DTS X, Auro3D, and DRA.Primary audio is loaded to the Primary memory buffer and the maximum audio bitrate (PCM) is 27.648 Mbps (3.456 MB memory). Only 32 audio streams are allowed for both Primary and Secondary streams, and the mandatory audio codecs are compressed using Constant Bitrate (CBR), while the optional codecs use Variable Bitrate (VBR).
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PCM | Dolby Digital | Dolby Digital Plus | Dolby TrueHD | Dolby Atmos | DTS Digital Surround | DTS-HD High Resolution Audio | DTS-HD Master Audio | DTS X | DRA | DRA extension | Auro 3D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Max. bitrate | 27.648 Mbit/s | 640 kbit/s | 4.736 Mbit/s | 18.64 Mbit/s | ? | 1.524 Mbit/s | 6.0 Mbit/s | 24.5 Mbit/s | ? | 1.5 Mbit/s | 3.0 Mbit/s | ? |
| Compression type | CBR | CBR | CBR | VBR | VBR | CBR | CBR | VBR | VBR | ? | ? | ? |
| Codec type | Uncompressed lossless | lossy | lossy | lossless | lossless | lossy | lossy | lossless | lossless | lossy | lossy | Uncompressed lossless |
| Max. channels | 8 (48kHz, 96kHz), 6 (192kHz) | 5.1 | 7.1 | 8 (48kHz, 96kHz), 6 (192kHz) | ? | 5.1 | 8 | 8 (48kHz, 96kHz), 6 (192kHz) | 8 | 5.1 | 7.1 | 11.1 |
| Bits/sample | 16, 20, 24 | 16, 24 | 16, 24 | 16, 24 | ? | 16, 20, 24 | 16, 20, 24 | 16, 20, 24 | ? | 16 | 16 | ? |
| Sampling Freq. | 48 kHz, 96 kHz, 192 kHz | 48 kHz | 48 kHz | 48 kHz, 96 kHz, 192 kHz | ? | 48 kHz, 96 kHz, 192 kHz | 48 kHz | 48 kHz, 96 kHz | ? | 48 kHz | 48 kHz, 96 kHz | ? |
| Max. streams | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 |
Secondary Audio[1]
Blu-ray also offers an audio mixing component that can play two audio streams simultaneously, Primary Audio and Secondary Audio. Secondary audio is loaded to the Primary memory buffer, it can go up to five channels in Dolby Digital Plus and DTS Express, both at a max bitrate of 256 kbit/s (32 KB memory), in 16-24 bit resolution at 48 kHz. It's usually used with Picture-in-Picture as a bonus feature played alongside the movie. It can also be used for additional sound effects in BD-J games.|
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Dolby Digital Plus | DTS Express |
|---|---|---|
| Max. bitrate | 256 Kbit/s | 256 Kbit/s |
| Compression type | CBR | CBR |
| Codec type | lossy | lossy |
| Max. channels | 5.1 | 5.1 |
| Bits/sample | 16, 24 | 16, 24 |
| Sampling Freq. | 48 kHz | 48 kHz |
Interactive Audio
Interactive Audio is used for real-time interactive sound effects, usually for menus or video games. It's preloaded to the sound memory buffer and exclusively uses PCM. See: Interactive Audio
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PCM |
|---|---|
| Max. Size | 2 MB[2] |
| Compression type | CBR |
| Codec type | lossless |
| Max. channels | 2 |
| Bits/sample | 16 |
| Sampling Freq. | 48 kHz |
Footnotes
[1] Ultra HD Blu-ray unfortunately does not support Secondary Audio. So, for example, if your making a video game for UHD, you'll won't have additional immersive audio.
[2] In HDMV mode, sound clips are stored in a single sound.bdmv file with a 2 MB max file size.
Author(s) : Æ Firestone
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