使用FFmpeg将字幕文件集成到视频文件

向视频文件里添加字幕是件很常见的事，本文使用FFmpeg将字幕文件集成到视频文件里。

在CentOS上编译安装FFmpeg

字幕文件转换

字幕文件有很多种，常见的有 .srt , .ass 文件等,下面使用FFmpeg进行相互转换。

将.srt文件转换成.ass文件

ffmpeg -i subtitle.srt subtitle.ass

将.ass文件转换成.srt文件

ffmpeg -i subtitle.ass subtitle.srt

集成字幕，选择播放

这种字幕集成比较简单，播放时需要在播放器中选择相应的字幕文件。

ffmpeg -i input.mp4 -i subtitles.srt -c:s mov_text -c:v copy -c:a copy output.mp4

嵌入SRT字幕到视频文件

单独SRT字幕

字幕文件为subtitle.srt

ffmpeg -i video.avi -vf subtitles=subtitle.srt out.avi

嵌入在MKV等容器的字幕

将video.mkv中的字幕（默认）嵌入到out.avi文件

ffmpeg -i video.mkv -vf subtitles=video.mkv out.avi

将video.mkv中的字幕（第二个）嵌入到out.avi文件

ffmpeg -i video.mkv -vf subtitles=video.mkv:si=1 out.avi

嵌入ASS字幕到视频文件

ffmpeg -i video.avi -vf "ass=subtitle.ass" out.avi

不能加载fontconfig文件

Fontconfig error: Cannot load default config file
[Parsed_ass_0 @ 0000000002bfa3e0] No usable fontconfig configuration file found,
 using fallback.
Fontconfig error: Cannot load default config file

出现类似错误的原因是无法加载字体配置文件。

环境变量

FFmpeg使用的默认字体文件是使用系统环境变量中对应的文件位置。

默认文件名：fonts.conf

环境变量 FONTCONFIG_FILE 可以覆盖默认配置文件
环境变量 FONTCONFIG_PATH 可以覆盖默认配置文件目录

Linux 默认配置文件：fonts.conf

使用步骤：

1. 以root权限登录
2. 建立/etc/fonts目录
3. 下载fonts.conf文件到/etc/fonts目录
4. 设置fonts.conf文件权限为可读

Linux/Mac 系统

在~/.bashrc 最后添加：

export FONTCONFIG_PATH=/opt/X11/lib/X11/fontconfig

使之有效：

source ~/.bashrc

编辑 /opt/X11/lib/X11/fontconfig/fonts.conf 在字体目录添加 /Library/Fonts

<!-- Font directory list -->

  <dir>/opt/X11/share/fonts</dir>
  <dir>/usr/X11R6/lib/X11/fonts</dir>
  <dir>~/.fonts</dir>
  <dir>/Library/Fonts</dir>

Windows系统

在系统环境变量中添加：

name: FONTCONFIG_PATH
value: J:/ffmpeg (我本机ffmpeg目录，与fonts.conf同目录即可)

将fonts.conf文件放至上述指定目录。

以下为使用的fonts.conf文件：

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<!-- /etc/fonts/fonts.conf file to configure system font access -->
<fontconfig>

<!--
	DO NOT EDIT THIS FILE.
	IT WILL BE REPLACED WHEN FONTCONFIG IS UPDATED.
	LOCAL CHANGES BELONG IN 'local.conf'.

	The intent of this standard configuration file is to be adequate for
	most environments.  If you have a reasonably normal environment and
	have found problems with this configuration, they are probably
	things that others will also want fixed.  Please submit any
	problems to the fontconfig bugzilla system located at fontconfig.org

	Note that the normal 'make install' procedure for fontconfig is to
	replace any existing fonts.conf file with the new version.  Place
	any local customizations in local.conf which this file references.

	Keith Packard
-->

<!-- Font directory list -->

	<dir>C:/Windows/Fonts</dir>
<!--
  Accept deprecated 'mono' alias, replacing it with 'monospace'
-->
	<match target="pattern">
		<test qual="any" name="family">
			<string>mono</string>
		</test>
		<edit name="family" mode="assign">
			<string>monospace</string>
		</edit>
	</match>

<!--
  Accept alternate 'sans serif' spelling, replacing it with 'sans-serif'
-->
	<match target="pattern">
		<test qual="any" name="family">
			<string>sans serif</string>
		</test>
		<edit name="family" mode="assign">
			<string>sans-serif</string>
		</edit>
	</match>

<!--
  Accept deprecated 'sans' alias, replacing it with 'sans-serif'
-->
	<match target="pattern">
		<test qual="any" name="family">
			<string>sans</string>
		</test>
		<edit name="family" mode="assign">
			<string>sans-serif</string>
		</edit>
	</match>

<!--
  Mark common families with their generics so we'll get
  something reasonable
-->

<!--
  Serif faces
 -->
	<alias>
		<family>Times New Roman</family>
		<default><family>serif</family></default>
	</alias>

<!--
  If the font still has no generic name, add sans-serif
 -->
	<match target="pattern">
		<test qual="all" name="family" compare="not_eq">
			<string>sans-serif</string>
		</test>
		<test qual="all" name="family" compare="not_eq">
			<string>serif</string>
		</test>
		<test qual="all" name="family" compare="not_eq">
			<string>monospace</string>
		</test>
		<edit name="family" mode="append_last">
			<string>sans-serif</string>
		</edit>
	</match>

<!--
 AMT provides metric and shape compatible fonts for these three web font
 families.
 -->
 	<alias>
		<family>Times New Roman</family>
		<accept><family>Thorndale AMT</family></accept>
	</alias>
 	<alias>
		<family>Arial</family>
		<accept><family>Albany AMT</family></accept>
	</alias>
 	<alias>
		<family>Courier New</family>
		<accept><family>Cumberland AMT</family></accept>
	</alias>
 
<!--
  Some Asian fonts misadvertise themselves as monospaced when
  in fact they are dual-spaced (half and full).  This makes
  FreeType very confused as it forces all widths to match.
  Undo this magic by disabling the width forcing code -->
	<match target="font">
		<test name="family"><string>GulimChe</string></test>
		<edit name="globaladvance"><bool>false</bool></edit>
	</match>

	<match target="font">
		<test name="family"><string>DotumChe</string></test>
		<edit name="globaladvance"><bool>false</bool></edit>
	</match>

	<match target="font">
		<test name="family"><string>BatangChe</string></test>
		<edit name="globaladvance"><bool>false</bool></edit>
	</match>

	<match target="font">
		<test name="family"><string>GungsuhChe</string></test>
		<edit name="globaladvance"><bool>false</bool></edit>
	</match>




	<config>
<!--
  These are the default Unicode chars that are expected to be blank
  in fonts.  All other blank chars are assumed to be broken and
  won't appear in the resulting charsets
 -->
		<blank>
			<int>0x0020</int>	<!-- SPACE -->
			<int>0x00A0</int>	<!-- NO-BREAK SPACE -->
			<int>0x00AD</int>	<!-- SOFT HYPHEN -->
			<int>0x034F</int>	<!-- COMBINING GRAPHEME JOINER -->
			<int>0x0600</int>	<!-- ARABIC NUMBER SIGN -->
			<int>0x0601</int>	<!-- ARABIC SIGN SANAH -->
			<int>0x0602</int>	<!-- ARABIC FOOTNOTE MARKER -->
			<int>0x0603</int>	<!-- ARABIC SIGN SAFHA -->
			<int>0x06DD</int>	<!-- ARABIC END OF AYAH -->
			<int>0x070F</int>	<!-- SYRIAC ABBREVIATION MARK -->
			<int>0x115F</int>	<!-- HANGUL CHOSEONG FILLER -->
			<int>0x1160</int>	<!-- HANGUL JUNGSEONG FILLER -->
			<int>0x1680</int>	<!-- OGHAM SPACE MARK -->
			<int>0x17B4</int>	<!-- KHMER VOWEL INHERENT AQ -->
			<int>0x17B5</int>	<!-- KHMER VOWEL INHERENT AA -->
			<int>0x180E</int>	<!-- MONGOLIAN VOWEL SEPARATOR -->
			<int>0x2000</int>	<!-- EN QUAD -->
			<int>0x2001</int>	<!-- EM QUAD -->
			<int>0x2002</int>	<!-- EN SPACE -->
			<int>0x2003</int>	<!-- EM SPACE -->
			<int>0x2004</int>	<!-- THREE-PER-EM SPACE -->
			<int>0x2005</int>	<!-- FOUR-PER-EM SPACE -->
			<int>0x2006</int>	<!-- SIX-PER-EM SPACE -->
			<int>0x2007</int>	<!-- FIGURE SPACE -->
			<int>0x2008</int>	<!-- PUNCTUATION SPACE -->
			<int>0x2009</int>	<!-- THIN SPACE -->
			<int>0x200A</int>	<!-- HAIR SPACE -->
			<int>0x200B</int>	<!-- ZERO WIDTH SPACE -->
			<int>0x200C</int>	<!-- ZERO WIDTH NON-JOINER -->
			<int>0x200D</int>	<!-- ZERO WIDTH JOINER -->
			<int>0x200E</int>	<!-- LEFT-TO-RIGHT MARK -->
			<int>0x200F</int>	<!-- RIGHT-TO-LEFT MARK -->
			<int>0x2028</int>	<!-- LINE SEPARATOR -->
			<int>0x2029</int>	<!-- PARAGRAPH SEPARATOR -->
			<int>0x202A</int>	<!-- LEFT-TO-RIGHT EMBEDDING -->
			<int>0x202B</int>	<!-- RIGHT-TO-LEFT EMBEDDING -->
			<int>0x202C</int>	<!-- POP DIRECTIONAL FORMATTING -->
			<int>0x202D</int>	<!-- LEFT-TO-RIGHT OVERRIDE -->
			<int>0x202E</int>	<!-- RIGHT-TO-LEFT OVERRIDE -->
			<int>0x202F</int>	<!-- NARROW NO-BREAK SPACE -->
			<int>0x205F</int>	<!-- MEDIUM MATHEMATICAL SPACE -->
			<int>0x2060</int>	<!-- WORD JOINER -->
			<int>0x2061</int>	<!-- FUNCTION APPLICATION -->
			<int>0x2062</int>	<!-- INVISIBLE TIMES -->
			<int>0x2063</int>	<!-- INVISIBLE SEPARATOR -->
			<int>0x206A</int>	<!-- INHIBIT SYMMETRIC SWAPPING -->
			<int>0x206B</int>	<!-- ACTIVATE SYMMETRIC SWAPPING -->
			<int>0x206C</int>	<!-- INHIBIT ARABIC FORM SHAPING -->
			<int>0x206D</int>	<!-- ACTIVATE ARABIC FORM SHAPING -->
			<int>0x206E</int>	<!-- NATIONAL DIGIT SHAPES -->
			<int>0x206F</int>	<!-- NOMINAL DIGIT SHAPES -->
			<int>0x3000</int>	<!-- IDEOGRAPHIC SPACE -->
			<int>0x3164</int>	<!-- HANGUL FILLER -->
			<int>0xFEFF</int>	<!-- ZERO WIDTH NO-BREAK SPACE -->
			<int>0xFFA0</int>	<!-- HALFWIDTH HANGUL FILLER -->
			<int>0xFFF9</int>	<!-- INTERLINEAR ANNOTATION ANCHOR -->
			<int>0xFFFA</int>	<!-- INTERLINEAR ANNOTATION SEPARATOR -->
			<int>0xFFFB</int>	<!-- INTERLINEAR ANNOTATION TERMINATOR -->
		</blank>
<!--
  Rescan configuration every 30 seconds when FcFontSetList is called
 -->
		<rescan>
			<int>30</int>
		</rescan>
	</config>

</fontconfig>