MP4文件quick start探究

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最近在Flash上实现MP4文件点播时，发现部分MP4文件在原有的播放器上无法播放，经过定位发现，原来是MP4 BOX搞的鬼！

什么是MP4 BOX？

对于一般的MP4文件，BOX顺序为：ftyp-moov-free-mdat.
而对于部分经过视频软件处理后的MP4文件，BOX顺序发生了改变：ftyp-free-mdat-moov.
对于这种顺序的MP4文件，在完整下载文件之前，无法获取moov信息，因此是无法实现边下载边播放的。

解决方案

对源文件进行重新编码
既然BOX顺序有问题，可以从源头上进行处理：调整BOX顺序。工具qt-faststart即是实现该功能的利器。
qt-faststart主页
下载了qt-faststart.exe binary for Windows之后，通过cmd对def.mp4文件进行转化： qt-faststart.exe def.mp4 def_new.mp4
转化后，box顺序果然发生了变化，播放正常。

使用AtomicParsley对MP4文件进行解析：

Atom ftyp @ 0 of size: 32, ends @ 32Atom free @ 32 of size: 8, ends @ 40Atom mdat @ 40 of size: 1025668, ends @ 1025708Atom moov @ 1025708 of size: 13925, ends @ 1039633     Atom mvhd @ 1025716 of size: 108, ends @ 1025824     Atom trak @ 1025824 of size: 6608, ends @ 1032432         Atom tkhd @ 1025832 of size: 92, ends @ 1025924         Atom edts @ 1025924 of size: 36, ends @ 1025960             Atom elst @ 1025932 of size: 28, ends @ 1025960         Atom mdia @ 1025960 of size: 6472, ends @ 1032432             Atom mdhd @ 1025968 of size: 32, ends @ 1026000             Atom hdlr @ 1026000 of size: 45, ends @ 1026045             Atom minf @ 1026045 of size: 6387, ends @ 1032432                 Atom vmhd @ 1026053 of size: 20, ends @ 1026073                 Atom dinf @ 1026073 of size: 36, ends @ 1026109                     Atom dref @ 1026081 of size: 28, ends @ 1026109                 Atom stbl @ 1026109 of size: 6323, ends @ 1032432                     Atom stsd @ 1026117 of size: 167, ends @ 1026284                         Atom avc1 @ 1026133 of size: 151, ends @ 1026284                             Atom avcC @ 1026219 of size: 49, ends @ 1026268                             Atom pasp @ 1026268 of size: 16, ends @ 1026284                 ~                     Atom stts @ 1026284 of size: 24, ends @ 1026308                     Atom stss @ 1026308 of size: 24, ends @ 1026332                     Atom ctts @ 1026332 of size: 3008, ends @ 1029340                     Atom stsc @ 1029340 of size: 40, ends @ 1029380                     Atom stsz @ 1029380 of size: 1532, ends @ 1030912                     Atom stco @ 1030912 of size: 1520, ends @ 1032432     Atom trak @ 1032432 of size: 7104, ends @ 1039536         Atom tkhd @ 1032440 of size: 92, ends @ 1032532         Atom edts @ 1032532 of size: 36, ends @ 1032568             Atom elst @ 1032540 of size: 28, ends @ 1032568         Atom mdia @ 1032568 of size: 6968, ends @ 1039536             Atom mdhd @ 1032576 of size: 32, ends @ 1032608             Atom hdlr @ 1032608 of size: 45, ends @ 1032653             Atom minf @ 1032653 of size: 6883, ends @ 1039536                 Atom smhd @ 1032661 of size: 16, ends @ 1032677                 Atom dinf @ 1032677 of size: 36, ends @ 1032713                     Atom dref @ 1032685 of size: 28, ends @ 1032713                 Atom stbl @ 1032713 of size: 6823, ends @ 1039536                     Atom stsd @ 1032721 of size: 103, ends @ 1032824                         Atom mp4a @ 1032737 of size: 87, ends @ 1032824                             Atom esds @ 1032773 of size: 51, ends @ 1032824                     Atom stts @ 1032824 of size: 24, ends @ 1032848                     Atom stsc @ 1032848 of size: 2524, ends @ 1035372                     Atom stsz @ 1035372 of size: 2644, ends @ 1038016                     Atom stco @ 1038016 of size: 1520, ends @ 1039536     Atom udta @ 1039536 of size: 97, ends @ 1039633         Atom meta @ 1039544 of size: 89, ends @ 1039633             Atom hdlr @ 1039556 of size: 33, ends @ 1039589             Atom ilst @ 1039589 of size: 44, ends @ 1039633                 Atom ?too @ 1039597 of size: 36, ends @ 1039633                     Atom data @ 1039605 of size: 28, ends @ 1039633 ~ denotes an unknown atom------------------------------------------------------Total size: 1039633 bytes; 51 atoms total. AtomicParsley version: 0.9.0 (utf16)Media data: 1025668 bytes; 13965 bytes all other atoms (1.343% atom overhead).Total free atom space: 8 bytes; 0.001% waste.------------------------------------------------------

修改后：

Atom ftyp @ 0 of size: 32, ends @ 32Atom moov @ 32 of size: 13925, ends @ 13957     Atom mvhd @ 40 of size: 108, ends @ 148     Atom trak @ 148 of size: 6608, ends @ 6756         Atom tkhd @ 156 of size: 92, ends @ 248         Atom edts @ 248 of size: 36, ends @ 284             Atom elst @ 256 of size: 28, ends @ 284         Atom mdia @ 284 of size: 6472, ends @ 6756             Atom mdhd @ 292 of size: 32, ends @ 324             Atom hdlr @ 324 of size: 45, ends @ 369             Atom minf @ 369 of size: 6387, ends @ 6756                 Atom vmhd @ 377 of size: 20, ends @ 397                 Atom dinf @ 397 of size: 36, ends @ 433                     Atom dref @ 405 of size: 28, ends @ 433                 Atom stbl @ 433 of size: 6323, ends @ 6756                     Atom stsd @ 441 of size: 167, ends @ 608                         Atom avc1 @ 457 of size: 151, ends @ 608                             Atom avcC @ 543 of size: 49, ends @ 592                             Atom pasp @ 592 of size: 16, ends @ 608         ~                     Atom stts @ 608 of size: 24, ends @ 632                     Atom stss @ 632 of size: 24, ends @ 656                     Atom ctts @ 656 of size: 3008, ends @ 3664                     Atom stsc @ 3664 of size: 40, ends @ 3704                     Atom stsz @ 3704 of size: 1532, ends @ 5236                     Atom stco @ 5236 of size: 1520, ends @ 6756     Atom trak @ 6756 of size: 7104, ends @ 13860         Atom tkhd @ 6764 of size: 92, ends @ 6856         Atom edts @ 6856 of size: 36, ends @ 6892             Atom elst @ 6864 of size: 28, ends @ 6892         Atom mdia @ 6892 of size: 6968, ends @ 13860             Atom mdhd @ 6900 of size: 32, ends @ 6932             Atom hdlr @ 6932 of size: 45, ends @ 6977             Atom minf @ 6977 of size: 6883, ends @ 13860                 Atom smhd @ 6985 of size: 16, ends @ 7001                 Atom dinf @ 7001 of size: 36, ends @ 7037                     Atom dref @ 7009 of size: 28, ends @ 7037                 Atom stbl @ 7037 of size: 6823, ends @ 13860                     Atom stsd @ 7045 of size: 103, ends @ 7148                         Atom mp4a @ 7061 of size: 87, ends @ 7148                             Atom esds @ 7097 of size: 51, ends @ 7148                     Atom stts @ 7148 of size: 24, ends @ 7172                     Atom stsc @ 7172 of size: 2524, ends @ 9696                     Atom stsz @ 9696 of size: 2644, ends @ 12340                     Atom stco @ 12340 of size: 1520, ends @ 13860     Atom udta @ 13860 of size: 97, ends @ 13957         Atom meta @ 13868 of size: 89, ends @ 13957             Atom hdlr @ 13880 of size: 33, ends @ 13913             Atom ilst @ 13913 of size: 44, ends @ 13957                 Atom ?too @ 13921 of size: 36, ends @ 13957                     Atom data @ 13929 of size: 28, ends @ 13957Atom free @ 13957 of size: 8, ends @ 13965Atom mdat @ 13965 of size: 1025668, ends @ 1039633 ~ denotes an unknown atom------------------------------------------------------Total size: 1039633 bytes; 51 atoms total. AtomicParsley version: 0.9.0 (utf16)Media data: 1025668 bytes; 13965 bytes all other atoms (1.343% atom overhead).Total free atom space: 8 bytes; 0.001% waste. Padding available: 8 bytes.------------------------------------------------------

客户端动态加载BOX
对于自有内容网站来说，对自身视频库进行转码并不麻烦。但是对于第三方公司来说，可能无法去对甲方庞大的视频库进行处理，更理想的方式，是从客户端及时获取moov信息并实现播放。

//TODO

参考文章：

http://blog.zhourunsheng.com/2012/05/android-视频播放之流媒体格式处理/
http://stackoverflow.com/questions/19803458/how-to-download-only-the-moov-atom-from-mp4-file

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