FFmpeg -strict -2 参数详解

FFmpeg -strict -2 的这个参数好多说的不太正确 好多都是说 -strict strictness 跟标准的严格性 解释的和实际含义差别很大 这里详细说明下:

ffmpeg -re -i /Users/Downloads/RelaxingGuitarMusic.3gp -vcodec copy -acodec copy -strict -2 -f flvrtmp://192.168.10.61:1935/zbcs/room

ffmpeg -re -i /Users/Downloads/RelaxingGuitarMusic.3gp -vcodec copy -acodec copy -strict -2 -f flvrtmp://localhost:1935/zbcs/room

ffmpeg -re -i /Users/Downloads/RelaxingGuitarMusic.3gp -vcodec libx264 -acodec aac -strict -2 -f flvrtmp://192.168.10.61:1935/zbcs/room

Native FFmpeg AAC encoder ¶

The native FFmpeg AAC encoder. This is currently the second highest-quality AAC encoder available in FFmpeg and does not require an external library like the other AAC encoders described here. This is the default AAC encoder.

Note: -strict experimental (or -strict -2) was previously required for this encoder, but it is  no longer experimental and these options are unnecessary since 5 December 2015.

-strict -2 之前是实验参数表示 aac音频编码 如果不使用aac音频编码使用使其的编码好像还需要导入第三方的音频编码库 比较麻烦 使用FFmpeg自带的aac音频编码要带上-strict -2 参数就可以了。带这个参数是为了使用aac音频编码。

https://zhidao.baidu.com/question/539258608.html

-sameq 指相同的量级数，常被误用成“相同的画质”，所以被取消。官方推荐用-qscale和-qmax替代

ffmpeg不支持libfaac库，faac库音质也一般。 
另支持2套AAC音频编码，
-acodec aac  是ffmpeg自制的AAC编码器，处在实验阶段，需要开启"-strict experimental"参数，音质也不差。
-acodec libvo_aacenc 是移植自安卓系统的AAC编码器，比较成熟。

追问

我测试发现-qmax或者-qscale 后面需要填一个数字，请问这个数字是什么含义呢？-sameq相同量级数是什么意思呢？谢谢

追答

xvid或x264之类的编码器对编码的程度有量化的级数。-sameq保持和输入时一样的级数，但再次有损编码进行编码，画质肯定会下降，所以不是一样的画质。-qmax n 声明变化级数编码时最大的级数整数n。  n的值由具体编码决定，x264是[0,51]之间。0代表最好，51最差-qscale  n 以固定的量化级数值n编码，x264是[0,51]之间。

追问

非常感谢！

参考地址：

http://trac.ffmpeg.org/wiki/Encode/AAC

Native FFmpeg AAC encoder ¶

The native FFmpeg AAC encoder. This is currently the second highest-quality AAC encoder available in FFmpeg and does not require an external library like the other AAC encoders described here. This is the default AAC encoder.

Note: -strict experimental (or -strict -2) was previously required for this encoder, but it is  no longer experimental and these options are unnecessary since 5 December 2015.

Example using -b:a

ffmpeg -i input.wav -c:a aac -b:a 160k output.m4a

Example using -q:a

ffmpeg -i input.wav -c:a aac -q:a 2 output.m4a

Effective range for -q:a is around 0.1-2. This VBR is experimental and likely to get even worse results than the CBR.