ALSA:不支持非交错访问吗? [英] ALSA: non-interleaved access not supported?

问题描述

ALSA的时，a>函数失败SND_PCM_ACCESS_RW_NONINTERLEAVED访问类型，报告存在无效的参数.相同的代码与 SND_PCM_AESS访问.

ALSA's snd_pcm_hw_params_set_access function fails when called with SND_PCM_ACCESS_RW_NONINTERLEAVED access type, reporting that there was an invalid argument. The same code works fine with SND_PCM_ACCESS_RW_INTERLEAVED access.

我试图更改对snd_pcm_hw_params_ *函数的调用顺序，但没有任何效果.

I tried to change the order of calls to snd_pcm_hw_params_* functions with no effect.

接下来，我认为我的硬件可能不支持非交错播放，但是根据

Next I thought that my hardware might not support non-interleaved playback, but according to this post ALSA subsystem will interleave non-interleaved data before sending it to the hardware if it does not support non-interleaved playback itself. Thus, non-interleaved access should always be available.

那为什么为什么不支持不交错的访问呢?

Why is it then, that non-interleaved access seems not be unsupported?

以下是适用于交错播放的代码，但对于非交错播放会产生此问题:

Following is the code that works fine for interleaved playback, but produces this problem for non-interleaved playback:

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.

这篇关于ALSA:不支持非交错访问吗?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！