[英]Alsa lib 32 bits
I've been trying to use the ALSA lib for a while and I don't understand how I should use it.我一直在尝试使用 ALSA lib,但我不明白我应该如何使用它。
I took an example program and I've tried to modify it to use float
(32bits) instead of unsigned char
(8bits).我拿了一个示例程序,我试图修改它以使用float
(32 位)而不是unsigned char
(8 位)。 But now when I'm running it, I have a segmentation fault in the second loop.但是现在当我运行它时,我在第二个循环中出现了分段错误。
Here is my code :这是我的代码:
#include <alsa/asoundlib.h>
snd_pcm_t *create_pcm(const char* name, snd_pcm_stream_t mode, snd_pcm_format_t format, snd_pcm_access_t access, unsigned int nbChannel, unsigned int rate, int softSample, unsigned int latency)
{
int err;
snd_pcm_t *handle;
if ((err = snd_pcm_open(&handle, name, mode, 0)) < 0) {
printf("Playback open error: %s\n", snd_strerror(err));
exit(EXIT_FAILURE);
}
if ((err = snd_pcm_set_params(handle,
format,
access,
nbChannel,
rate,
softSample,
latency)) < 0) { /* 0.5sec */
printf("Playback open error: %s\n", snd_strerror(err));
exit(EXIT_FAILURE);
}
return handle;
}
int main(void)
{
unsigned int i;
snd_pcm_t *handle;
snd_pcm_sframes_t frames;
float buffer[16*1024]; /* some random data */
handle = create_pcm("default", // name of the device used by the sound card
SND_PCM_STREAM_PLAYBACK, // to use the device in output
SND_PCM_FORMAT_FLOAT, // use the device with 32bit depth (float)
SND_PCM_ACCESS_RW_INTERLEAVED,
1, // use 1 channel
48000, // use 48000 Hz (dvd quality)
1, // soft resample ON
500000); // 0.5s of latency
// building random data
for(i = 0; i < sizeof(buffer); i++)
buffer[i] = i % 255; // random();
for (i = 0; i < 16; i++) {
frames = snd_pcm_writei(handle, buffer, sizeof(buffer)); // segmentation fault
if(frames < 0)
frames = snd_pcm_recover(handle, frames, 0);
if (frames < 0) {
printf("snd_pcm_writei failed: %s\n", snd_strerror(frames));
break;
}
if (frames > 0 && frames < (long)sizeof(buffer))
printf("Short write (expected %li, wrote %li)\n", (long)sizeof(buffer), frames);
}
snd_pcm_close(handle);
return 0;
}
How to use this lib with 32bits?如何将这个库与 32 位一起使用?
I've tried this format and others like little endian or big endian.. The only one that doesn't crash is SND_PCM_FORMAT_FLOAT
but it's making the error :我已经尝试过这种格式和其他像 little endian 或 big endian .. 唯一不会崩溃的SND_PCM_FORMAT_FLOAT
是SND_PCM_FORMAT_FLOAT
但它正在犯错误:
ALSA lib pcm.c:8507:(snd_pcm_set_params) Sample format not available for PLAYBACK: Invalid argument
Playback open error: Invalid argument
Thanks in advance.提前致谢。
PS: Linux, Ubuntu 19.10 64bits PS:Linux,Ubuntu 19.10 64 位
The segmentation fault may already occur when you write into buffer
:写入buffer
时可能已经发生分段错误:
for(i = 0; i < sizeof(buffer); i++)
buffer[i] = i % 255; // random();
sizeof(buffer)
will give you the size in bytes not the number of elements. sizeof(buffer)
会给你以字节为单位的大小而不是元素的数量。 They are only equal for char
(and unsigned char
) since sizeof(char)
is 1
.它们仅对char
(和unsigned char
)相等,因为sizeof(char)
是1
。 You most likely want to iterate over the elements:您最有可能想要遍历元素:
for(i = 0; i < sizeof buffer/sizeof *buffer; i++)
buffer[i] = i % 255; // random();
It was indeed a problem of condition in my loop and my snd_pcm_writei()
这确实是我的循环和我的snd_pcm_writei()
的条件问题
Here is the code without errors thanks to @Osiris :由于@Osiris,这是没有错误的代码:
#include <alsa/asoundlib.h>
snd_pcm_t *create_pcm(const char* name, snd_pcm_stream_t mode, snd_pcm_format_t format, snd_pcm_access_t access, unsigned int nbChannel, unsigned int rate, int softSample, unsigned int latency)
{
int err;
snd_pcm_t *handle;
if ((err = snd_pcm_open(&handle, name, mode, 0)) < 0) {
printf("Playback open error: %s\n", snd_strerror(err));
exit(EXIT_FAILURE);
}
if ((err = snd_pcm_set_params(handle,
format,
access,
nbChannel,
rate,
softSample,
latency)) < 0) { /* 0.5sec */
printf("Playback open error: %s\n", snd_strerror(err));
exit(EXIT_FAILURE);
}
return handle;
}
int main(void)
{
unsigned int i;
snd_pcm_t *handle;
snd_pcm_sframes_t frames;
float buffer[16*1024]; /* some random data */
handle = create_pcm("default", // name of the device used by the sound card
SND_PCM_STREAM_PLAYBACK, // to use the device in output
SND_PCM_FORMAT_FLOAT, // use the device with 32bit depth (float)
SND_PCM_ACCESS_RW_INTERLEAVED,
1, // use 1 channel
48000, // use 48000 Hz (dvd quality)
1, // soft resample ON
500000); // 0.5s of latency
// building random data
for(i = 0; i < sizeof(buffer) / sizeof(*buffer); i++)
buffer[i] = i % 0xffffffff; // random();
for (i = 0; i < 16; i++) {
frames = snd_pcm_writei(handle, buffer, sizeof(buffer) / sizeof(*buffer)); // segmentation fault
if(frames < 0)
frames = snd_pcm_recover(handle, frames, 0);
if (frames < 0) {
printf("snd_pcm_writei failed: %s\n", snd_strerror(frames));
break;
}
if (frames > 0 && frames < (long)(sizeof(buffer) / sizeof(*buffer)))
printf("Short write (expected %li, wrote %li)\n", (long)sizeof(buffer), frames);
}
snd_pcm_close(handle);
return 0;
}
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