使用ffmpeg将ASS字幕打进视频流中
在某些视频格式标准中（也就是容器中）是不支持字幕的，例如将mkv文件转码成为ts文件或者mp4文件后，有时候会发现字幕不翼而飞了，这对有些英语不是很好，需要看到字幕的人就不那么顺利了。不过没关系，在转码的时候，可以将字幕打入视频流中，这样就可以在播视频时，将字幕输出出来了，具体方法如下：
首先要了解字幕又很多种，例如srt，例如txt，还有其他的格式，不过这里主要分享的时ASS的
[*]首先要使用已经支持ass的ffmpeg，怎么才能确定ffmpeg是否已经支持ass了呢：
可以通过ffmpeg -codecs参数来查看 $ ffmpeg -codecs|grep ass
ffmpeg version N-65018-gad91bf8 Copyright (c) 2000-2014 the FFmpeg developers
built on Jul 27 2014 20:36:24 with Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
configuration: --enable-opengl --enable-libx265 --enable-libx264 --enable-libmp3lame --enable-gpl --enable-libfaac --enable-nonfree --prefix=/usr/ --enable-libfreetype --enable-libass
libavutil 52. 92.101 / 52. 92.101
libavcodec 55. 69.100 / 55. 69.100
libavformat 55. 49.100 / 55. 49.100
libavdevice 55. 13.102 / 55. 13.102
libavfilter 4. 11.102 /4. 11.102
libswscale 2.6.100 /2.6.100
libswresample 0. 19.100 /0. 19.100
libpostproc 52.3.100 / 52.3.100
DES... ass ASS (Advanced SSA) subtitle
$ 从上面的倒数第二行中可以看到，已经支持了ASS的解码，编码；可以找到ass的字幕文件，文件内容大致如下：$ head -n 30 ~/Downloads/a.ass
Title: AMV For Dreamers Subtitle
ScriptType: v4.00+
WrapStyle: 0
ScaledBorderAndShadow: yes
Collisions: Normal
Scroll Position: 37
Active Line: 38
Video Zoom Percent: 0.5
PlayResX: 720
PlayResY: 480
Last Style Storage: Default
Video Aspect Ratio: c1.5
Video Position: 5818
YCbCr Matrix: TV.601
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: Default,Arial,20,&H00FFFFFF,&H000000FF,&H00000000,&H00000000,0,0,0,0,100,100,0,0,1,2,2,2,10,10,10,1
Style: Lyric,Adobe 黑体 Std R,24,&H14FFFFFF,&H000000FF,&H326A31DE,&H32272732,-1,0,0,0,100,100,0,0,1,1.5,1,1,20,20,16,1
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.36,0:00:23.21,Lyric,,0,0,0,,敬启 读着这封信的你
Dialogue: 0,0:00:23.21,0:00:29.22,Lyric,,0,0,0,,你在哪里 做些什么呢？
Dialogue: 0,0:00:30.69,0:00:34.63,Lyric,,0,0,0,,十五岁的我
Dialogue: 0,0:00:34.63,0:00:44.49,Lyric,,0,0,0,,有着无法向任何人诉说的烦恼
Dialogue: 0,0:00:46.05,0:00:53.69,Lyric,,0,0,0,,如果是写给未来的自己的信的话
Dialogue: 0,0:00:53.69,0:00:59.95,Lyric,,0,0,0,,想必一定能坦率地说出口吧
Dialogue: 0,0:01:00.65,0:01:04.62,Lyric,,0,0,0,,此刻 快要认输 快要落泪
$ 找到了对应的文件以后，可以考虑将该文件的字幕打入到对应的视频文件中，下面聚一个例子：$ ffmpeg -i ~/Movies/objectC/facebook.mp4 -i ~/Downloads/a.ass -vf ass=~/Downloads/a.ass a.ts
ffmpeg version N-65018-gad91bf8 Copyright (c) 2000-2014 the FFmpeg developers
built on Jul 27 2014 20:36:24 with Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
configuration: --enable-opengl --enable-libx265 --enable-libx264 --enable-libmp3lame --enable-gpl --enable-libfaac --enable-nonfree --prefix=/usr/ --enable-libfreetype --enable-libass
libavutil 52. 92.101 / 52. 92.101
libavcodec 55. 69.100 / 55. 69.100
libavformat 55. 49.100 / 55. 49.100
libavdevice 55. 13.102 / 55. 13.102
libavfilter 4. 11.102 /4. 11.102
libswscale 2.6.100 /2.6.100
libswresample 0. 19.100 /0. 19.100
libpostproc 52.3.100 / 52.3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Users/StevenLiu/Movies/objectC/facebook.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf55.22.102
description : bbs.chinaffmpeg.com 孙悟空
Duration: 02:00:27.85, start: 0.000000, bitrate: 893 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x480, 797 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 87 kb/s (default)
Metadata:
handler_name : SoundHandler
Input #1, ass, from '/Users/StevenLiu/Downloads/a.ass':
Duration: N/A, bitrate: N/A
Stream #1:0: Subtitle: ssa
Added subtitle file: '/Users/StevenLiu/Downloads/a.ass' (3 styles, 51 events)
Output #0, mpegts, to 'a.ts':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
description : bbs.chinaffmpeg.com 孙悟空
encoder : Lavf55.49.100
Stream #0:0(und): Video: mpeg2video, yuv420p, 640x480, q=2-31, 200 kb/s, 25 fps, 90k tbn, 25 tbc (default)
Metadata:
handler_name : VideoHandler
encoder : Lavc55.69.100 mpeg2video
Stream #0:1(und): Audio: mp2, 44100 Hz, stereo, s16, 384 kb/s (default)
Metadata:
handler_name : SoundHandler
encoder : Lavc55.69.100 mp2
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> mpeg2video (native))
Stream #0:1 -> #0:1 (aac (native) -> mp2 (native))
Press to stop, [?] for help
Fontconfig warning: ignoring UTF-8: not a valid region tag
fontconfig: cannot find font 'Adobe 黑体 Std R', falling back to 'Verdana106 Negreta'
Glyph 0x656C not found, selecting one more font for (Adobe 黑体 Std R, 200, 0)
fontconfig: cannot find glyph U+656C in font 'Adobe 黑体 Std R', falling back to 'MS Gothic'
Glyph 0x8BFB not found, selecting one more font for (Adobe 黑体 Std R, 200, 0)
fontconfig: cannot find glyph U+8BFB in font 'Adobe 黑体 Std R', falling back to 'SimSun'
frame= 3163 fps=461 q=31.0 Lsize= 11136kB time=00:02:06.64 bitrate= 720.3kbits/s
video:3877kB audio:5935kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 13.490704%
根据上面的内容可以看到，在输入的内容中，有音频流，视频流，还有字幕流，但是输出的内容中，只有视频流，音频流，并且输出的文件为ts，接下来看一下效果：
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