MKV parser and quick seek.

最新推荐文章于 2021-02-23 19:47:15 发布

原创最新推荐文章于 2021-02-23 19:47:15 发布 · 1.1k 阅读

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文章标签：

#class #system #file #each #basic #search

本文深入探讨了MKV文件格式的组成结构，包括元数据索引、轨道信息、章节、集群等部分，并详细解释了如何通过元数据索引进行高效定位与解码关键元素。同时介绍了MKV文件中数据大小的编码方式，以及如何计算数据大小。最后讨论了MKV文件格式在技术应用中的优势与局限性。

1： seek the File's problem.

文件各个部分介绍：

The Metaseek section contains an index of where all of the other groups are in the file are located, such as the Track information, Chapters, Tags, Cues, Attachments, and so on. This element isn't technicaly required, but you would have to search the entire file to find all of the other Level 1 elements if you did not have it. This is because any of the items can occur in any order. For instance you could have the chapters section in the middle of the Clusters. This is part of the flexibility of EBML and Matroksa.

The Track section has basic information about each of the tracks.

The Clusters section has all of the Clusters. These contain all of the video frames and audio for each track.

解码关键：

判断标志位size. 例如：1A 45 DF A3 1A = 0001 1010 . size = 4. (000 +1)

Element ID coded with an UTF-8 like system :

bits, big-endian

1xxx xxxx                                  - Class A IDs (2^7 -1 possible values) (base 0x8X)

01xx xxxx  xxxx xxxx                       - Class B IDs (2^14-1 possible values) (base 0x4X 0xXX)

001x xxxx  xxxx xxxx  xxxx xxxx            - Class C IDs (2^21-1 possible values) (base 0x2X 0xXX 0xXX)

0001 xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx - Class D IDs (2^28-1 possible values) (base 0x1X 0xXX 0xXX 0xXX)

同样道理。计算data size.

比如：1A 45 DF A3 A3 . size = 1010 0011 size = 1, value = 10 0011= 35!

Data size, in octets, is also coded with an UTF-8 like system :

bits, big-endian

1xxx xxxx                                                                              - value 0 to  2^7-2

01xx xxxx  xxxx xxxx                                                                   - value 0 to 2^14-2

001x xxxx  xxxx xxxx  xxxx xxxx                                                        - value 0 to 2^21-2

0001 xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx                                             - value 0 to 2^28-2

0000 1xxx  xxxx xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx                                  - value 0 to 2^35-2

0000 01xx  xxxx xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx                       - value 0 to 2^42-2

0000 001x  xxxx xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx            - value 0 to 2^49-2

0000 0001  xxxx xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx - value 0 to 2^56-2



MKV 文件格式类似一个单链表。顺序解析方便。

但是seek就很不方便。

Meta seek infomation 往往没有实际意义。