PCM转PCMA（pcm_alaw，G711.A率）转换表 PCM转PCMU（pcm_ulaw，G711.U率）转换表
PCM转PCMA（pcm_alaw，G711.A率）转换表 && PCM转PCMU（pcm_ulaw，G711.U率）转换表
文章目录
- PCM转PCMA（pcm_alaw，G711.A率）转换表 && PCM转PCMU（pcm_ulaw，G711.U率）转换表
- ffmpeg源码生成转码表
- 使用方式
- 生成源码
ffmpeg源码生成转码表
最近要做一个功能，int16_t的PCM数据转为uint8的PCMA数据，
网上的不太可信，找ffmpeg库，发现ffmpeg库使用的是查表发实现的，
而且还有现成的生成表数据的源代码，可信度非常高
/** Generate a header file for hardcoded PCM tables** Copyright (c) 2010 Reimar Döffinger <Reimar.Doeffinger@gmx.de>** This file is part of FFmpeg.** FFmpeg is free software; you can redistribute it and/or* modify it under the terms of the GNU Lesser General Public* License as published by the Free Software Foundation; either* version 2.1 of the License, or (at your option) any later version.** FFmpeg is distributed in the hope that it will be useful,* but WITHOUT ANY WARRANTY; without even the implied warranty of* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU* Lesser General Public License for more details.** You should have received a copy of the GNU Lesser General Public* License along with FFmpeg; if not, write to the Free Software* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA*/#include <stdlib.h>
#define CONFIG_HARDCODED_TABLES 0
#include "pcm_tablegen.h"
#include "tableprint.h"int main(void)
{pcm_alaw_tableinit();pcm_ulaw_tableinit();pcm_vidc_tableinit();write_fileheader();WRITE_ARRAY("static const", uint8_t, linear_to_alaw);WRITE_ARRAY("static const", uint8_t, linear_to_ulaw);WRITE_ARRAY("static const", uint8_t, linear_to_vidc);return 0;
}
编译上有些小问题，没太关注，直接使用了注释大法，
没有用的统统干掉，编译通过，执行生成转换映射表。
不用再去研究转换公式，直接对照着表查询结果即可。
拿走不谢
使用方式
可参照ffmpeg源代码pcm.c使用
case AV_CODEC_ID_PCM_ALAW:for (; n > 0; n--) {v = *samples++;*dst++ = linear_to_alaw[(v + 32768) >> 2];}break;case AV_CODEC_ID_PCM_MULAW:for (; n > 0; n--) {v = *samples++;*dst++ = linear_to_ulaw[(v + 32768) >> 2];}break;
PCM有符号，加上32768变成正数除以4查表即可。
生成源码
表数据太大，CSDN不让保存，放到我个人服务器上了（大神手下留情不要攻击）。
http://118.126.97.61:8084/src_libs/ffmpeg_pcm_table/