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

1. 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

[StevenLiu@localhost ffmpeg]$ 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
[StevenLiu@localhost ffmpeg]$

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：

[StevenLiu@localhost ffmpeg]$ head -n 30 ~/Downloads/a.ass
[Script Info]
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

[V4+ Styles]
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

[Events]
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
[StevenLiu@localhost ffmpeg]$

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：

[StevenLiu@localhost ffmpeg]$ 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 : bbs.chinaffmpeg.com 孙悟空
    description : This File is Created by Easy RealMedia Tools@!
  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
[Parsed_ass_0 @ 0x7fad1b40c5e0] 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 : This File is Created by Easy RealMedia Tools@!
    encoder : bbs.chinaffmpeg.com 孙悟空
    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 [q] to stop, [?] for help
Fontconfig warning: ignoring UTF-8: not a valid region tag
[Parsed_ass_0 @ 0x7fad1b40c5e0] fontconfig: cannot find font 'Adobe 黑体 Std R', falling back to 'Verdana106 Negreta'
[Parsed_ass_0 @ 0x7fad1b40c5e0] Glyph 0x656C not found, selecting one more font for (Adobe 黑体 Std R, 200, 0)
[Parsed_ass_0 @ 0x7fad1b40c5e0] fontconfig: cannot find glyph U+656C in font 'Adobe 黑体 Std R', falling back to 'MS Gothic'
[Parsed_ass_0 @ 0x7fad1b40c5e0] Glyph 0x8BFB not found, selecting one more font for (Adobe 黑体 Std R, 200, 0)
[Parsed_ass_0 @ 0x7fad1b40c5e0] 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：