[轉]多媒體封裝格式詳解---MP4
原文 https://www.cnblogs.com/jingzhishen/p/3698570.html
參考 http://www.cnblogs.com/ranson7zop/p/7889272.html
http://blog.csdn.net/pirateleo/article/details/7061452
一、基本概念
1、 檔案,由許多Box和FullBox組成。
2、 Box,每個Box由Header和Data組成。
3、 FullBox,是Box的擴充套件,Box結構的基礎上在Header中增加8bits version和24bits flags。
4、 Header,包含了整個Box的長度size和型別type。當size==0時,代表這是檔案中最後一個Box;當size==1時,意 味著Box長度需要更多bits來描述,在後面會定義一個64bits的largesize描述Box的長度;當type是uuid時,代表Box中的數 據是使用者自定義擴充套件型別。
5、 Data,是Box的實際資料,可以是純資料也可以是更多的子Boxes。
6、 當一個Box的Data中是一系列子Box時,這個Box又可成為Container Box。
結構如下圖:
檔案基本結構描述圖
1、 ftypbox,在檔案的開始位置,描述的檔案的版本、相容協議等;
2、 moovbox,這個box中不包含具體媒體資料,但包含本檔案中所有媒體資料的巨集觀描述資訊,moov box下有mvhd和trak box。
>>mvhd中記錄了建立時間、修改時間、時間度量標尺、可播放時長等資訊。
>>trak中的一系列子box描述了每個媒體軌道的具體資訊。
3、 moofbox,這個box是視訊分片的描述資訊。並不是MP4檔案必須的部分,但在我們常見的可線上播放的MP4格式檔案中(例如Silverlight Smooth Streaming中的ismv檔案)確是重中之重
4、 mdatbox,實際媒體資料。我們最終解碼播放的資料都在這裡面。
5、 mfrabox,一般在檔案末尾,媒體的索引檔案,可通過查詢直接定位所需時間點的媒體資料。
附:Smooth Streaming中ismv檔案結構,檔案分為了多個Fragments,每個Fragment中包含moof和mdat。這樣的結構符合漸進式播放需求。(mdat及其描述資訊逐步傳輸,收齊一個Fragment便可播放其中的mdat)。
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static int mov_read_ftyp(MOVContext *c, AVIOContext *pb, MOVAtom atom)
{
uint32_t minor_ver;
int comp_brand_size;
char minor_ver_str[11]; /* 32 bit integer -> 10 digits + null */
char* comp_brands_str;
uint8_t type[5] = {0};
avio_read(pb, type, 4);
if (strcmp(type, "qt "))
c->isom = 1;
av_log(c->fc, AV_LOG_DEBUG, "ISO: File Type Major Brand: %.4s\n",(char *)&type);
av_dict_set(&c->fc->metadata, "major_brand", type, 0);
minor_ver = avio_rb32(pb); /* minor version */
snprintf(minor_ver_str, sizeof(minor_ver_str), "%"PRIu32"", minor_ver);
av_dict_set(&c->fc->metadata, "minor_version", minor_ver_str, 0);
comp_brand_size = atom.size - 8;
if (comp_brand_size < 0)
return AVERROR_INVALIDDATA;
comp_brands_str = av_malloc(comp_brand_size + 1); /* Add null terminator */
if (!comp_brands_str)
return AVERROR(ENOMEM);
avio_read(pb, comp_brands_str, comp_brand_size);
comp_brands_str[comp_brand_size] = 0;
av_dict_set(&c->fc->metadata, "compatible_brands", comp_brands_str, 0);
av_freep(&comp_brands_str);
return 0;
}
二、MP4檔案格式(ISO-14496-12/14)
MP4檔案概述
MP4檔案就是由各式各樣的Box組成的,下表中列出了所有必選或可選的Box型別,√代表Box必選。
具體列表:
ftyp |
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√ |
file type and compatibility |
pdin |
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progressive download information |
moov |
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√ |
container for all the metadata |
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mvhd |
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√ |
movie header, overall declarations |
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trak |
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√ |
container for an individual track or stream |
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tkhd |
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√ |
track header, overall information about the track |
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tref |
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track reference container |
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edts |
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edit list container |
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elst |
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an edit list |
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mdia |
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√ |
container for the media information in a track |
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mdhd |
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√ |
media header, overall information about the media |
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hdlr |
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√ |
handler, declares the media (handler) type |
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minf |
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√ |
media information container |
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vmhd |
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video media header, overall information (video track only) |
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smhd |
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sound media header, overall information (sound track only) |
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hmhd |
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hint media header, overall information (hint track only) |
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nmhd |
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Null media header, overall information (some tracks only) |
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dinf |
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√ |
data information box, container |
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dref |
√ |
data reference box, declares source(s) of media data in track |
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stbl |
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√ |
sample table box, container for the time/space map |
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stsd |
√ |
sample descriptions (codec types, initialization etc.) |
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stts |
√ |
(decoding) time-to-sample |
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ctts |
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(composition) time to sample |
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stsc |
√ |
sample-to-chunk, partial data-offset information |
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stsz |
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sample sizes (framing) |
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stz2 |
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compact sample sizes (framing) |
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stco |
√ |
chunk offset, partial data-offset information |
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co64 |
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64-bit chunk offset |
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stss |
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sync sample table (random access points) |
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stsh |
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shadow sync sample table |
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padb |
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sample padding bits |
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stdp |
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sample degradation priority |
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sdtp |
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independent and disposable samples |
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sbgp |
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sample-to-group |
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sgpd |
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sample group description |
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subs |
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sub-sample information |
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mvex |
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movie extends box |
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mehd |
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movie extends header box |
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trex |
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√ |
track extends defaults |
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ipmc |
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IPMP Control Box |
moof |
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movie fragment |
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mfhd |
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√ |
movie fragment header |
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traf |
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track fragment |
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tfhd |
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√ |
track fragment header |
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trun |
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track fragment run |
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sdtp |
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independent and disposable samples |
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sbgp |
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sample-to-group |
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subs |
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sub-sample information |
mfra |
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movie fragment random access |
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tfra |
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track fragment random access |
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mfro |
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√ |
movie fragment random access offset |
mdat |
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media data container |
free |
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free space |
skip |
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free space |
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udta |
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user-data |
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cprt |
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copyright etc. |
meta |
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metadata |
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hdlr |
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√ |
handler, declares the metadata (handler) type |
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dinf |
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data information box, container |
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dref |
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data reference box, declares source(s) of metadata items |
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ipmc |
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IPMP Control Box |
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iloc |
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item location |
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ipro |
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item protection |
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sinf |
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protection scheme information box |
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frma |
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original format box |
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imif |
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IPMP Information box |
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schm |
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scheme type box |
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schi |
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scheme information box |
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iinf |
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item information |
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xml |
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XML container |
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bxml |
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binary XML container |
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pitm |
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primary item reference |
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fiin |
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file delivery item information |
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paen |
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partition entry |
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fpar |
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file partition |
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fecr |
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FEC reservoir |
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segr |
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file delivery session group |
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gitn |
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group id to name |
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tsel |
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track selection |
meco |
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additional metadata container |
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mere |
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metabox relation |
正式開始前先對檔案的幾個重要部分巨集觀介紹一下,以便諸位在後續學習時心中有數:
1、 ftypbox,在檔案的開始位置,描述的檔案的版本、相容協議等;
2、 moovbox,這個box中不包含具體媒體資料,但包含本檔案中所有媒體資料的巨集觀描述資訊,moov box下有mvhd和trak box。
>>mvhd中記錄了建立時間、修改時間、時間度量標尺、可播放時長等資訊。
>>trak中的一系列子box描述了每個媒體軌道的具體資訊。
3、 moofbox,這個box是視訊分片的描述資訊。並不是MP4檔案必須的部分,但在我們常見的可線上播放的MP4格式檔案中(例如Silverlight Smooth Streaming中的ismv檔案)確是重中之重。
4、 mdatbox,實際媒體資料。我們最終解碼播放的資料都在這裡面。
5、 mfrabox,一般在檔案末尾,媒體的索引檔案,可通過查詢直接定位所需時間點的媒體資料。
附:Smooth Streaming中ismv檔案結構,檔案分為了多個Fragments,每個Fragment中包含moof和mdat。這樣的結構符合漸進式播放需求。(mdat及其描述資訊逐步傳輸,收齊一個Fragment便可播放其中的mdat)。
http://blog.csdn.net/tx3344/article/details/8476669
MP4(MPEG-4 Part 14)是一種常見的多媒體容器格式,它是在“ISO/IEC 14496-14”標準檔案中定義的。
1.最小組成單元 BOX
像FLV的tag、MKV的EBML、ASF檔案中的 ASF object.mp4 是由一系列的box組成,他的最小組成單元就是box.
size;指明瞭整個box所佔用的大小,包括header部分.
type;表示這個box的型別。(附表1)
largesize;如果box很大超過了uint32的最大數值,size就被設定為1,並用接下來的 largesize來存放大小。
2.mp4檔案整體結構
mp4檔案說白了就是一系列box組成,大box裡面有小box。
接下來會深入到具體的box裡面,來具體分析mp4格式
未完待續.....
附表1
Code | Abstract | Defined in/by |
ainf | Asset information to identify, license and play | DECE |
albm | Album title and track number (user-data) | 3GPP |
auth | Media author name (user-data) | 3GPP |
avcn | AVC NAL Unit Storage Box | DECE |
bloc | Base location and purchase location for license acquisition | DECE |
bpcc | Bits per component | JP2 |
buff | Buffering information | AVC |
bxml | binary XML container | ISO |
ccid | OMA DRM Content ID | OMA DRM 2.1 |
cdef | type and ordering of the components within the codestream | JP2 |
clsf | Media classification (user-data) | 3GPP |
cmap | mapping between a palette and codestream components | JP2 |
co64 | 64-bit chunk offset | ISO |
colr | specifies the colourspace of the image | JP2 |
cprt | copyright etc. (user-data) | ISO |
crhd | reserved for ClockReferenceStream header | MP4V1 |
cslg | composition to decode timeline mapping | ISO |
ctts | (composition) time to sample | ISO |
cvru | OMA DRM Cover URI | OMA DRM 2.1 |
dcfD | Marlin DCF Duration, user-data atom type | OMArlin |
dinf | data information box, container | ISO |
dref | data reference box, declares source(s) of media data in track | ISO |
dscp | Media description (user-data) | 3GPP |
dsgd | DVB Sample Group Description Box | DVB |
dstg | DVB Sample to Group Box | DVB |
edts | edit list container | ISO |
elst | an edit list | ISO |
feci | FEC Informatiom | ISO |
fecr | FEC Reservoir | ISO |
fiin | FD Item Information | ISO |
fire | File Reservoir | ISO |
fpar | File Partition | ISO |
free | free space | ISO |
frma | original format box | ISO |
ftyp | file type and compatibility | JP2, ISO |
gitn | Group ID to name | ISO |
gnre | Media genre (user-data) | 3GPP |
grpi | OMA DRM Group ID | OMA DRM 2.0 |
hdlr | handler, declares the media (handler) type | ISO |
hmhd | hint media header, overall information (hint track only) | ISO |
hpix | Hipix Rich Picture (user-data or meta-data) | HIPIX |
icnu | OMA DRM Icon URI | OMA DRM 2.0 |
ID32 | ID3 version 2 container | inline |
idat | Item data | ISO |
ihdr | Image Header | JP2 |
iinf | item information | ISO |
iloc | item location | ISO |
imif | IPMP Information box | ISO |
infu | OMA DRM Info URL | OMA DRM 2.0 |
iods | Object Descriptor container box | MP4V1 |
iphd | reserved for IPMP Stream header | MP4V1 |
ipmc | IPMP Control Box | ISO |
ipro | item protection | ISO |
iref | Item reference | ISO |
jP$20$20 | JPEG 2000 Signature | JP2 |
jp2c | JPEG 2000 contiguous codestream | JP2 |
jp2h | Header | JP2 |
jp2i | intellectual property information | JP2 |
kywd | Media keywords (user-data) | 3GPP |
loci | Media location information (user-data) | 3GPP |
lrcu | OMA DRM Lyrics URI | OMA DRM 2.1 |
m7hd | reserved for MPEG7Stream header | MP4V1 |
mdat | media data container | ISO |
mdhd | media header, overall information about the media | ISO |
mdia | container for the media information in a track | ISO |
mdri | Mutable DRM information | OMA DRM 2.0 |
meco | additional metadata container | ISO |
mehd | movie extends header box | ISO |
mere | metabox relation | ISO |
meta | Metadata container | ISO |
mfhd | movie fragment header | ISO |
mfra | Movie fragment random access | ISO |
mfro | Movie fragment random access offset | ISO |
minf | media information container | ISO |
mjhd | reserved for MPEG-J Stream header | MP4V1 |
moof | movie fragment | ISO |
moov | container for all the meta-data | ISO |
mvcg | Multiview group | AVC |
mvci | Multiview Information | AVC |
mvex | movie extends box | ISO |
mvhd | movie header, overall declarations | ISO |
mvra | Multiview Relation Attribute | AVC |
nmhd | Null media header, overall information (some tracks only) | ISO |
ochd | reserved for ObjectContentInfoStream header | MP4V1 |
odaf | OMA DRM Access Unit Format | OMA DRM 2.0 |
odda | OMA DRM Content Object | OMA DRM 2.0 |
odhd | reserved for ObjectDescriptorStream header | MP4V1 |
odhe | OMA DRM Discrete Media Headers | OMA DRM 2.0 |
odrb | OMA DRM Rights Object | OMA DRM 2.0 |
odrm | OMA DRM Container | OMA DRM 2.0 |
odtt | OMA DRM Transaction Tracking | OMA DRM 2.0 |
ohdr | OMA DRM Common headers | OMA DRM 2.0 |
padb | sample padding bits | ISO |
paen | Partition Entry | ISO |
pclr | palette which maps a single component in index space to a multiple- component image | JP2 |
pdin | Progressive download information | ISO |