语音助手开发小记（2023.9.25）

通道问题

       在使用函数swr_alloc_set_opts给SwrContext传递输入输出的音频参数时，需要设置通道，这里通道为2，但是通道布局不能传递2.比如AV_CH_LAYOUT_STEREO 实际值为3

如果要计算通道布局的通道数使用函数av_get_channel_layout_nb_channels

int src_nb_channels = av_get_channel_layout_nb_channels(src_ch_layout);

swr_ctx = swr_alloc_set_opts(nullptr,
	dst_wave_fmt.ch_layout, //输出通道
	dst_wave_fmt.sample_fmt, //输出样本格式
	dst_wave_fmt.rate, //输出采样率
	AV_CH_LAYOUT_STEREO_DOWNMIX,  //输入通道
	src_wave_fmt.sample_fmt,  //输入样本格式
	src_wave_fmt.rate, //输入采样率
	0, nullptr);

声道map定义在 libavutil/channel_layout.c文件中

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, },
    { "22.2",          24, AV_CH_LAYOUT_22POINT2, },
};

PCMA播放问题

播放PCMA

ffplay -f s16le -ar 8000 -acodec pcm_alaw -ac 1 src.pcma

播放PCMU

ffplay -f s16le -ar 8000 -acodec pcm_mulaw -ac 1 src.pcmu