“The Origin of Ogg Vorbis” Part 2
By the way, there is an item called “stream serial number” in the header. Ogg can handle multiple data streams and OggStream on the Xiph.Org website As shown in the figure at the bottom of the explain page, you can compose a file by mixing three streams of red, light blue, and green.
In this case, it will be shuffled page by page, so it is necessary to indicate “what flow data I have” on each page. This is indicated by the serial number of the sequence.
·Table 1
item name Size Content
capture_pattern Four OggS
stream_structure_version 1 0x00
header_type_flag 1 The Bitstream type that the page stores.
absolute position of granules 8 If Bitstream leaves this page, its location
stream serial number Four Bit stream number
page sequence no Four page number
Checksum Page Four 32-bit CRC Value
page_segments 1 Size of bit stream to store (bytes)
■ Vorbis characteristics
Vorbis, on the other hand, comes from the name of the main character in Terry Pratchett’s novel “Small Gods.” Basically, it has very similar characteristics to MP3s. Specifically, it has the following characteristics, and it is a “slightly better than MP3” number.
-Uses MDCT (Modified Discrete Cosine Transform)
-The sampling rate is 8 KHz to 192 KHz
-Precision
sampling is 16/24
bits -Maximum number of channels is 255 channels Bit rate is not uniquely determined as described below. The goal is to ensure a quality that beats MP3 at the same bit rate compared to the average bit rate, and the quality is generally said to be roughly the same as AAC.
On the other hand, there are some differences. The most important point is that the bit rate is only “VBR (Variable Bit Rate)”. MP3 uses “CBR (constant bit rate)”, so in summary, the playing time and the file size are in a proportional relationship.
In Vorbis, on the other hand, both timbre and play time are related to file size, and as a result, the file size is roughly the same as MP3 for the more complicated timbre and smaller for the more complicated timbre. simple. it is one of the factors for better sound quality than MP3 if it has the same bit rate. However, on the other hand, the fact that the processing required to encode / decode is definitely more than MP3 is a disadvantage of Vorbis.
■ The future of Ogg Vorbis
Ogg Vorbis is implemented on multiple platforms and, in addition to Windows / Mac OS / UNIX / LINUX, OS / 2 and Pocket PC players are available as standard. However, the official source is limited to providing the necessary libraries (and a simple interface).
In addition to this, for example, plugins for Windows Media Player and media players like WinAMP support it as standard, and groundwork is being prepared. However, the following factors can be considered as the reasons why it has not been widely used. -Is not
much better than MP3-There is no
a lot of support in portable players
Especially for the second point, the following problems are likely to exist.
-Since both encoding and decoding have a higher load than MP3, processing with a portable player is a bit heavy, and as a result there are disadvantages such as a reduction in continuous playback time.
-It does not have a copyright protection feature (this is from Xiph.org) as it is not set as a policy), it is unlikely to be used for music distribution which is popular these days,
and although it is not recognized that it is necessary to back it up with a portable player, there are cases in which music is distributed with Ogg Vorbis little by little, I am beginning to see it and I think that little by little it will increase its power in the future. However, to become a major format, you need some kind of opportunity, but it is a bit disappointing that such a move seems not to be that particular so far.
