int err;
if ((err = snd_pcm_hw_params_malloc(&hw_params)) < 0) {
fprintf(stderr, "ALSA: allocate hw_params error: %s\n", snd_strerror(err));
throw 5;
}
if ((err = snd_pcm_hw_params_any(pb_dev, hw_params)) < 0) {
fprintf(stderr, "ALSA: hw_params_any error: %s\n", snd_strerror(err));
throw 5;
}
if ((err = snd_pcm_hw_params_set_access(pb_dev, hw_params, (pAudioCtx->sample_fmt < AV_SAMPLE_FMT_U8P) ? SND_PCM_ACCESS_RW_INTERLEAVED : SND_PCM_ACCESS_RW_NONINTERLEAVED)) < 0) {
fprintf(stderr, "ALSA: set access type error: %s\n", snd_strerror(err));
throw 5;
}
if ((err = snd_pcm_hw_params_set_channels(pb_dev, hw_params, pAudioCtx->channels)) < 0) {
fprintf(stderr, "ALSA: set channel count error: %s\n", snd_strerror(err));
throw 5;
}
snd_pcm_format_t sample_format;
switch (pAudioCtx->sample_fmt) {
case AV_SAMPLE_FMT_U8: case AV_SAMPLE_FMT_U8P: sample_format = SND_PCM_FORMAT_U8; break;
case AV_SAMPLE_FMT_S16: case AV_SAMPLE_FMT_S16P: sample_format = SND_PCM_FORMAT_S16; break;
case AV_SAMPLE_FMT_S32: case AV_SAMPLE_FMT_S32P: sample_format = SND_PCM_FORMAT_S32; break;
case AV_SAMPLE_FMT_FLT: case AV_SAMPLE_FMT_FLTP: sample_format = SND_PCM_FORMAT_FLOAT; break;
case AV_SAMPLE_FMT_DBL: case AV_SAMPLE_FMT_DBLP: sample_format = SND_PCM_FORMAT_FLOAT64; break;
default: fprintf(stderr, "sampleformat %d is not supported\n", pAudioCtx->sample_fmt);
throw 5;
}
if ((err = snd_pcm_hw_params_set_format(pb_dev, hw_params, sample_format)) < 0) {
fprintf(stderr, "ALSA: set sample format error: %s\n", snd_strerror(err));
throw 5;
}
if ((err = snd_pcm_hw_params_set_rate_near(pb_dev, hw_params, (unsigned int*)&pAudioCtx->sample_rate, 0)) < 0) {
fprintf(stderr, "ALSA: set sample rate error: %s\n", snd_strerror(err));
throw 5;
}
if ((err = snd_pcm_hw_params(pb_dev, hw_params)) < 0) {
fprintf(stderr, "ALSA: set parameters error: %s\n", snd_strerror(err));
throw 5;
}
执行此操作将产生以下输出:
Executing this yields following output:
ALSA: set access type error: Invalid argument
推荐答案
hw_params_set _ * 函数仅接受设备支持的那些值.
The hw_params_set_* functions accept only those values that are supported by the device.
大多数默认设备( plughw ， default 等)支持自动转换，因此可以接受所有格式.硬件设备没有.
Most of the default devices (plughw, default, etc.) support automatic conversions, and thus accept all formats.hw devices do not.
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