The primary rival to HD DVD is Blu-ray, championed by Sony. Blu-ray has a higher disc capacity per layer (25 GB vs 15 GB). However the majority of Blu-ray titles released before 2007 are in the 25 GB single layer format while almost all HD DVD movies are in the 30 GB dual layer format.The first 50GB release for Blu-Ray was not made until November 2006. So far in 2007 approx half of the new releases for Blu-ray movies were released in 25GB Discs with the other half being released in 50GB dual layer format.
In terms of audio/video compression, HD DVD and Blu-ray are similar on the surface: both support MPEG-2, VC-1, and H.264 for video compression. Virtually every HD DVD released uses an advanced codec (VC-1 or H.264) for video compression, re
ducing the required space for equivalent quality video. The first generation of Blu-ray Disc movies however used the legacy video codec, and many new titles still do. In terms of audio, there are many differences. With HD DVD support for the new Dolby Digital Pluss audio codec is mandatory at a maximum of 3.0 Mbit/s, but for Blu-ray players it is optional at a maximum of 1.7 Mbit/s. Furthermore HD DVD players must be able to decode the new losslesss audio codec Dolby True HD, but this is optional for Blu-ray players.
Both HD DVD and Blu-ray Disc support the 24pp (traditional movie) frame rate, but technical implementations of this mode are different among the two formats. Blu-ray Disc supports 24p with its native timing, while HD DVD uses 60i timing for 24p (encoded progressively, replacing missing fields with "repeat field flags"). Decoders can ignore the “flags” to output 24p. There is no impact on picture resolution or storage space as a result of this, as the HD DVD format uses the exact same video information — it simply adds notational overhead.
In terms of audio/video compression, HD DVD and Blu-ray are similar on the surface: both support MPEG-2, VC-1, and H.264 for video compression. Virtually every HD DVD released uses an advanced codec (VC-1 or H.264) for video compression, re
ducing the required space for equivalent quality video. The first generation of Blu-ray Disc movies however used the legacy video codec, and many new titles still do. In terms of audio, there are many differences. With HD DVD support for the new Dolby Digital Pluss audio codec is mandatory at a maximum of 3.0 Mbit/s, but for Blu-ray players it is optional at a maximum of 1.7 Mbit/s. Furthermore HD DVD players must be able to decode the new losslesss audio codec Dolby True HD, but this is optional for Blu-ray players.Both HD DVD and Blu-ray Disc support the 24pp (traditional movie) frame rate, but technical implementations of this mode are different among the two formats. Blu-ray Disc supports 24p with its native timing, while HD DVD uses 60i timing for 24p (encoded progressively, replacing missing fields with "repeat field flags"). Decoders can ignore the “flags” to output 24p. There is no impact on picture resolution or storage space as a result of this, as the HD DVD format uses the exact same video information — it simply adds notational overhead.
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