介绍
mp4⽂件格式⼜被称为MPEG-4 Part 14，出⾃MPEG-4标准第14部分 。它是⼀种多媒体格式容器，⼴泛⽤于包装视频和⾳频数据流、海报、字幕和元数据等。（顺便⼀提，⽬前流⾏的视频编码格式AVC/H264
定义在MPEG-4 Part 10）。
概述
mp4⽂件由box组成，每个box分为Header和Data。其中Header部分包含了box的类型和⼤⼩，Data包含了⼦box或者数据，box可以嵌套⼦box。
下图是⼀个典型mp4⽂件的基本结构：
MP4⽂件的基本组成单元是box，也就是说MP4⽂件是由各种各样的box组成的，有parent box，还有children box。因此，这些boxes之间存在⼀定的层次关系，总结如下表所示，表中标记出了各个box必选或可选特性，√代表Box必选。
| ftyp | √ | file type and compatibility ⽂件类型和兼容性 | |||||
| pdin | progressive download information | ||||||
| moov | √ | container for all the metadata 所有元数据的容器 | |||||
| mvhd | √ | movie header, overall declarations 电影头，整体声明 | |||||
| trak | √ | container for an individual track or stream 单个轨或流的容器 | |||||
| tkhd | √ | track header, overall information about the track 轨的头部，关于该轨的概括信息，⽐如视频宽⾼ | |||||
| tref | track reference container | ||||||
| edts | edit list container | ||||||
| elst | an edit list | ||||||
| mdia | √ | container for the media information in a track 轨媒体信息的容器 | |||||
| mdhd | √ | media header, overall information about the media 媒体头，关于媒体的总体信息 | |||||
| hdlr | √ | handler, declares the media (handler) type 媒体的播放过程信息 | |||||
| minf | √ | media information container 媒体信息容器 | |||||
| vmhd | video media header, overall information (video track only) | ||||||
| smhd | sound media header, overall information (sound track only) | ||||||
| hmhd | hint media header, overall information (hint track only) | ||||||
| nmhd | Null media header, overall information (some tracks only) | ||||||
| dinf | √ | data information box, container 数据信息box，容器 | |||||
| dref | √ | data reference box, declares source(s) of media data in track 如何定位媒体信息 | |||||
| stbl | √ | sample table box, container for the time/space map 包含了track中的sample的所有时间和位置信息，以及sample的编解码等信息。利⽤这个表可以解析sample的时序、类型、⼤⼩以及在各⾃存储容器中的位置。 | |||||
| stsd | √ | sample descriptions (codec types,initialization etc.) 如果是视频，包含：编码类型、宽⾼、⻓度等信息；如果是⾳频，包含：声道、采样率等信息 | |||||
| stts | √ | (decoding) time-to-sample描述了sample时序的映射⽅法，我们可以通过它找到任何时间的sample。 | |||||
| ctts | (composition) time to sample。 | ||||||
| stsc | √ | sample-to-chunk, partial data-offset information ⽤chunk组织sample可以⽅便优化数据获取，⼀个chunk包含⼀个或多个sample。 | |||||
| stsz | sample sizes (framing) 每个sample的⼤⼩。虽然这⾥没有打勾，但对于mp4还是⾮常必要的。 | ||||||
| stz2 | compact sample sizes (framing) | ||||||
| stco | √ | chunk offset, partial data-offset information 定义了每个chunk在媒体流中的偏移位置 | |||||
| co64 | 64-bit chunk offset | ||||||
| stss | sync sample table (random access points) ⽤于确定media中的关键帧 | ||||||
| stsh | shadow sync sample table | ||||||
| padb | sample padding bits | ||||||
| stdp | sample degradation priority | ||||||
| sdtp | independent and disposable samples | ||||||
| sbgp | sample-to-group | ||||||
| sgpd | sample group description | ||||||
| subs | sub-sample information | ||||||
| mvex | movie extends box | ||||||
| mehd | movie extends header box | ||||||
| trex | √ | track extends defaults | |||||
| ipmc | IPMP Control Box | ||||||
| moof | movie fragment | ||||||
| mfhd | √ | movie fragment header | |||||
| traf | track fragment | ||||||
| tfhd | √ | track fragment header | |||||
| trun | track fragment run | ||||||
| sdtp | independent and disposable samples | ||||||
| sbgp | sample-to-group | ||||||
| subs | sub-sample information | ||||||
| mfra | movie fragment random access | ||||||
| tfra | track fragment random access | ||||||
| mfro | √ | movie fragment random access offset | |||||
| mdat | media data container | ||||||
| free | free space | ||||||
| skip | free space | ||||||
| udta | user-data | ||||||
| cprt | copyright etc. | ||||||
| meta | metadata | ||||||
| hdlr | √ | handler, declares the metadata (handler) type | |||||
| dinf | data information box, container | ||||||
| dref | data reference box, declares source(s) of metadata items | ||||||
| ipmc | IPMP Control Box | ||||||
| iloc | item location | ||||||
| ipro | item protection | ||||||
| sinf | protection scheme information box | ||||||
| frma | original format box | ||||||
| imif | IPMP Information box | ||||||
| schm | scheme type box | ||||||
| schi | scheme information box | ||||||
| iinf | item information | ||||||
| xml | XML container | ||||||
| bxml | binary XML container | ||||||
| pitm | primary item reference | ||||||
| fiin | file delivery item information | ||||||
| paen | partition entry | ||||||
| fpar | file partition | ||||||
| fecr | FEC reservoir | ||||||
| segr | file delivery session group | ||||||
| gitn | group id to name | ||||||
| tsel | track selection | ||||||
| meco | additional metadata container | ||||||
| mere | metabox relation |
本⽂使⽤mediainfo和mp4box进⾏分析
图中看到mp4⽂件由⼏个主要组成部分，下⾯以
标签：10,3780,Sample,--,chunk,bytes,音视频,sample,flag From： https://www.cnblogs.com/waitmoon/p/17375337.html