ffmpeg # probesize & analyzeduration

ffmpeg在avformat_find_stream_info中会读取一部分源文件的音视频数据，来分析文件信息，那么这个 *** 作读取多少数据呢?

答案是： 通过probesize和analyzeduration两个参数来控制 。

直接用命令行查看这两个参数:

-probesize和 -analyzeduration定义在 libavformat/options_table.h 中

可以看到probesize默认为5000000， 而analyzeduration默认为0.

传入的参数保存在 libavformat/avformat.h 中AVFormatContext的probesize和max_analyze_duration变量中。

从上可以看出 probesize是从源文件中读取的最大字节数，单位为字节。

max_analyze_duration是从文件中读取的最大时长，单位为 AV_TIME_BASE units 。

probesize的单位是字节。

最小是32字节。

默认是 5000000字节。

avformat_find_stream_info函数中:

可以看到analyzeduration参数不设置时，即analyzeduration默认等于0时，可以看到 默认的分析时长为5秒 :

而如果是flv文件的时候, 默认为90秒 ：

mpeg和mpegts文件的时候，默认7秒 :

结论是: 谁先达到就听谁的 。

以上的例子是读取50M的数据或100秒的数据，那个标准先达到，那就听谁的，停止probe 。

ffmpeg/doc/ffmpeg-formats.texi

ffmpeg/doc/faq.texi

https://ffmpeg.org/ffmpeg-formats.html

常见的MIME类型 超文本标记语言文本 .html text/html xml文档 .xml text/xml XHTML文档 .xhtml application/xhtml+xml 普通文本 .txt text/plain RTF文本 .rtf application/rtf PDF文档 .pdf application/pdf Microsoft Word文件 .word application/msword PNG图像 .png image/png GIF图形 .gif image/gif JPEG图形 .jpeg,.jpg image/jpeg au声音文件 .au audio/basic MIDI音乐文件 mid,.midi audio/midi,audio/x-midi RealAudio音乐文件 .ra, .ram audio/x-pn-realaudio MPEG文件 .mpg,.mpeg video/mpeg AVI文件 .avi video/x-msvideo GZIP文件 .gz application/x-gzip TAR文件 .tar application/x-tar 任意的二进制数据 application/octet-stream

是对服务器返回数据的一个说明指定浏览器如何解析,

content="text/html" 表示返回的内容是文本格式的html,

下面是不同的格式文件对应的content-type

.ppt - application/mspowerpoint

.ai - application/postscript

.aif - audio/x-aiff

.aifc - audio/x-aiff

.aiff - audio/x-aiff

.asc - text/plain

.au - audio/basic

.avi - video/x-msvideo

.bcpio - application/x-bcpio

.bin - application/octet-stream

.c - text/plain

.cc - text/plain

.ccad - application/clariscad

.cdf - application/x-netcdf

.class - application/octet-stream

.cpio - application/x-cpio

.cpt - application/mac-compactpro

.csh - application/x-csh

.css - text/css

.dcr - application/x-director

.dir - application/x-director

.dms - application/octet-stream

.doc - application/msword

.drw - application/drafting

.dvi - application/x-dvi

.dwg - application/acad

.dxf - application/dxf

.dxr - application/x-director

.eps - application/postscript

.etx - text/x-setext

.exe - application/octet-stream

.ez - application/andrew-inset

.f - text/plain

.f90 - text/plain

.fli - video/x-fli

.gif - image/gif

.gtar - application/x-gtar

.gz - application/x-gzip

.h - text/plain

.hdf - application/x-hdf

.hh - text/plain

.hqx - application/mac-binhex40

.htm - text/html

.html - text/html

.ice - x-conference/x-cooltalk

.ief - image/ief

.iges - model/iges

.igs - model/iges

.ips - application/x-ipscript

.ipx - application/x-ipix

.jpe - image/jpeg

.jpeg - image/jpeg

.jpg - image/jpeg

.js - application/x-javascript

.kar - audio/midi

.latex - application/x-latex

.lha - application/octet-stream

.lsp - application/x-lisp

.lzh - application/octet-stream

.m - text/plain

.man - application/x-troff-man

.me - application/x-troff-me

.mesh - model/mesh

.mid - audio/midi

.midi - audio/midi

.mif - application/vnd.mif

.mime - www/mime

.mov - video/quicktime

.movie - video/x-sgi-movie

.mp2 - audio/mpeg

.mp3 - audio/mpeg

.mpe - video/mpeg

.mpeg - video/mpeg

.mpg - video/mpeg

.mpga - audio/mpeg

.ms - application/x-troff-ms

.msh - model/mesh

.nc - application/x-netcdf

.oda - application/oda

.pbm - image/x-portable-bitmap

.pdb - chemical/x-pdb

.pdf - application/pdf

.pgm - image/x-portable-graymap

.pgn - application/x-chess-pgn

.png - image/png

.pnm - image/x-portable-anymap

.pot - application/mspowerpoint

.ppm - image/x-portable-pixmap

.pps - application/mspowerpoint

.ppt - application/mspowerpoint

.ppz - application/mspowerpoint

.pre - application/x-freelance

.prt - application/pro_eng

.ps - application/postscript

.qt - video/quicktime

.ra - audio/x-realaudio

.ram - audio/x-pn-realaudio

.ras - image/cmu-raster

.rgb - image/x-rgb

.rm - audio/x-pn-realaudio

.roff - application/x-troff

.rpm - audio/x-pn-realaudio-plugin

.rtf - text/rtf

.rtx - text/richtext

.scm - application/x-lotusscreencam

.set - application/set

.sgm - text/sgml

.sgml - text/sgml

.sh - application/x-sh

.shar - application/x-shar

.silo - model/mesh

.sit - application/x-stuffit

.skd - application/x-koan

.skm - application/x-koan

.skp - application/x-koan

.skt - application/x-koan

.smi - application/smil

.smil - application/smil

.snd - audio/basic

.sol - application/solids

.spl - application/x-futuresplash

.src - application/x-wais-source

.step - application/STEP

.stl - application/SLA

.stp - application/STEP

.sv4cpio - application/x-sv4cpio

.sv4crc - application/x-sv4crc

.swf - application/x-shockwave-flash

.t - application/x-troff

.tar - application/x-tar

.tcl - application/x-tcl

.tex - application/x-tex

.texi - application/x-texinfo

.texinfo - application/x-texinfo

.tif - image/tiff

.tiff - image/tiff

.tr - application/x-troff

.tsi - audio/TSP-audio

.tsp - application/dsptype

.tsv - text/tab-separated-values

.txt - text/plain

.unv - application/i-deas

.ustar - application/x-ustar

.vcd - application/x-cdlink

.vda - application/vda

.viv - video/vnd.vivo

.vivo - video/vnd.vivo

.vrml - model/vrml

.wav - audio/x-wav

.wrl - model/vrml

.wml - text/vnd.wap.wml

.xbm - image/x-xbitmap

.xlc - application/vnd.ms-excel

.xll - application/vnd.ms-excel

.xlm - application/vnd.ms-excel

.xls - application/vnd.ms-excel

.xlw - application/vnd.ms-excel

.xml - text/xml

.xpm - image/x-xpixmap

.xwd - image/x-xwindowdump

.xyz - chemical/x-pdb

.zip - application/zip

charset="utf-8"要求浏览器以utf-8这种编码解析内容

常用的编码还有gbk即 charset="gbk"

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