如何将FFmpeg音频的声道布局和声道数修改为特定长尾词配置？

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前言：FFmpeg在libavutil模块封装了获取声道布局、声道名称与声道数的API，包括声道布局、单声道、立体声、环绕声道等。具体声道包括：5.0声道、5.1声道、7.0声道、7.1声道等。声道编码包包括：前方左、前方右等。

前言

FFmpeg在libavutil模块封装有获取声道布局、声道名字与声道数的API

声道布局

包括：单声道、立体声道、环绕声道、5.0声道、5.1声道、7.0声道、7.1声道等。声道掩码包括：前方左边、前方右边、前方中央、低频、后方左边、后方右边、后方中央、左环绕、右环绕等。声道布局、声道数和声道名字可以互相转换

FFmpeg相关宏定义

libavutil/channel_layout.h

/** * @} * @defgroup channel_mask_c Audio channel layouts * @{ * */ #define AV_CH_LAYOUT_MONO (AV_CH_FRONT_CENTER) #define AV_CH_LAYOUT_STEREO (AV_CH_FRONT_LEFT|AV_CH_FRONT_RIGHT) #define AV_CH_LAYOUT_2POINT1 (AV_CH_LAYOUT_STEREO|AV_CH_LOW_FREQUENCY) #define AV_CH_LAYOUT_2_1 (AV_CH_LAYOUT_STEREO|AV_CH_BACK_CENTER) #define AV_CH_LAYOUT_SURROUND (AV_CH_LAYOUT_STEREO|AV_CH_FRONT_CENTER) #define AV_CH_LAYOUT_3POINT1 (AV_CH_LAYOUT_SURROUND|AV_CH_LOW_FREQUENCY) #define AV_CH_LAYOUT_4POINT0 (AV_CH_LAYOUT_SURROUND|AV_CH_BACK_CENTER) #define AV_CH_LAYOUT_4POINT1 (AV_CH_LAYOUT_4POINT0|AV_CH_LOW_FREQUENCY) #define AV_CH_LAYOUT_2_2 (AV_CH_LAYOUT_STEREO|AV_CH_SIDE_LEFT|AV_CH_SIDE_RIGHT) #define AV_CH_LAYOUT_QUAD (AV_CH_LAYOUT_STEREO|AV_CH_BACK_LEFT|AV_CH_BACK_RIGHT) #define AV_CH_LAYOUT_5POINT0 (AV_CH_LAYOUT_SURROUND|AV_CH_SIDE_LEFT|AV_CH_SIDE_RIGHT) #define AV_CH_LAYOUT_5POINT1 (AV_CH_LAYOUT_5POINT0|AV_CH_LOW_FREQUENCY) #define AV_CH_LAYOUT_5POINT0_BACK (AV_CH_LAYOUT_SURROUND|AV_CH_BACK_LEFT|AV_CH_BACK_RIGHT) #define AV_CH_LAYOUT_5POINT1_BACK (AV_CH_LAYOUT_5POINT0_BACK|AV_CH_LOW_FREQUENCY) #define AV_CH_LAYOUT_6POINT0 (AV_CH_LAYOUT_5POINT0|AV_CH_BACK_CENTER) #define AV_CH_LAYOUT_6POINT0_FRONT (AV_CH_LAYOUT_2_2|AV_CH_FRONT_LEFT_OF_CENTER|AV_CH_FRONT_RIGHT_OF_CENTER) #define AV_CH_LAYOUT_HEXAGONAL (AV_CH_LAYOUT_5POINT0_BACK|AV_CH_BACK_CENTER) #define AV_CH_LAYOUT_6POINT1 (AV_CH_LAYOUT_5POINT1|AV_CH_BACK_CENTER) #define AV_CH_LAYOUT_6POINT1_BACK (AV_CH_LAYOUT_5POINT1_BACK|AV_CH_BACK_CENTER) #define AV_CH_LAYOUT_6POINT1_FRONT (AV_CH_LAYOUT_6POINT0_FRONT|AV_CH_LOW_FREQUENCY) #define AV_CH_LAYOUT_7POINT0 (AV_CH_LAYOUT_5POINT0|AV_CH_BACK_LEFT|AV_CH_BACK_RIGHT) #define AV_CH_LAYOUT_7POINT0_FRONT (AV_CH_LAYOUT_5POINT0|AV_CH_FRONT_LEFT_OF_CENTER|AV_CH_FRONT_RIGHT_OF_CENTER) #define AV_CH_LAYOUT_7POINT1 (AV_CH_LAYOUT_5POINT1|AV_CH_BACK_LEFT|AV_CH_BACK_RIGHT) #define AV_CH_LAYOUT_7POINT1_WIDE (AV_CH_LAYOUT_5POINT1|AV_CH_FRONT_LEFT_OF_CENTER|AV_CH_FRONT_RIGHT_OF_CENTER) #define AV_CH_LAYOUT_7POINT1_WIDE_BACK (AV_CH_LAYOUT_5POINT1_BACK|AV_CH_FRONT_LEFT_OF_CENTER|AV_CH_FRONT_RIGHT_OF_CENTER) #define AV_CH_LAYOUT_OCTAGONAL (AV_CH_LAYOUT_5POINT0|AV_CH_BACK_LEFT|AV_CH_BACK_CENTER|AV_CH_BACK_RIGHT) #define AV_CH_LAYOUT_HEXADECAGONAL (AV_CH_LAYOUT_OCTAGONAL|AV_CH_WIDE_LEFT|AV_CH_WIDE_RIGHT|AV_CH_TOP_BACK_LEFT|AV_CH_TOP_BACK_RIGHT|AV_CH_TOP_BACK_CENTER|AV_CH_TOP_FRONT_CENTER|AV_CH_TOP_FRONT_LEFT|AV_CH_TOP_FRONT_RIGHT) #define AV_CH_LAYOUT_STEREO_DOWNMIX (AV_CH_STEREO_LEFT|AV_CH_STEREO_RIGHT)

libavutil/channel_layout.c

static const struct { const char *name; int nb_channels; uint64_t layout; } channel_layout_map[] = { { "mono", 1, AV_CH_LAYOUT_MONO }, { "stereo", 2, AV_CH_LAYOUT_STEREO }, { "2.1", 3, AV_CH_LAYOUT_2POINT1 }, { "3.0", 3, AV_CH_LAYOUT_SURROUND }, { "3.0(back)", 3, AV_CH_LAYOUT_2_1 }, { "4.0", 4, AV_CH_LAYOUT_4POINT0 }, { "quad", 4, AV_CH_LAYOUT_QUAD }, { "quad(side)", 4, AV_CH_LAYOUT_2_2 }, { "3.1", 4, AV_CH_LAYOUT_3POINT1 }, { "5.0", 5, AV_CH_LAYOUT_5POINT0_BACK }, { "5.0(side)", 5, AV_CH_LAYOUT_5POINT0 }, { "4.1", 5, AV_CH_LAYOUT_4POINT1 }, { "5.1", 6, AV_CH_LAYOUT_5POINT1_BACK }, { "5.1(side)", 6, AV_CH_LAYOUT_5POINT1 }, { "6.0", 6, AV_CH_LAYOUT_6POINT0 }, { "6.0(front)", 6, AV_CH_LAYOUT_6POINT0_FRONT }, { "hexagonal", 6, AV_CH_LAYOUT_HEXAGONAL }, { "6.1", 7, AV_CH_LAYOUT_6POINT1 }, { "6.1(back)", 7, AV_CH_LAYOUT_6POINT1_BACK }, { "6.1(front)", 7, AV_CH_LAYOUT_6POINT1_FRONT }, { "7.0", 7, AV_CH_LAYOUT_7POINT0 }, { "7.0(front)", 7, AV_CH_LAYOUT_7POINT0_FRONT }, { "7.1", 8, AV_CH_LAYOUT_7POINT1 }, { "7.1(wide)", 8, AV_CH_LAYOUT_7POINT1_WIDE_BACK }, { "7.1(wide-side)", 8, AV_CH_LAYOUT_7POINT1_WIDE }, { "octagonal", 8, AV_CH_LAYOUT_OCTAGONAL }, { "hexadecagonal", 16, AV_CH_LAYOUT_HEXADECAGONAL }, { "downmix", 2, AV_CH_LAYOUT_STEREO_DOWNMIX, }, };

FFmpeg相关参数

AVCodec *pAudioCodec = avcodec_find_encoder(AV_CODEC_ID_AAC); AVCodecContext *pAudioCodecContext = avcodec_alloc_context3(pAudioCodec); pAudioCodecContext->sample_fmt = AV_SAMPLE_FMT_FLTP; pAudioCodecContext->sample_rate = 8000; pAudioCodecContext->channel_layout = AV_CH_LAYOUT_MONO; pAudioCodecContext->channels = av_get_channel_layout_nb_channels(pAudioCodecContext->channel_layout);

当前的音频数据采样频率是8000，单声道，浮点型采样位深

单声道AV_CH_LAYOUT_MONO，然后根据声道布局获取声道个数av_get_channel_layout_nb_channels，避免了使用数字1，2，3这种写法