如何在C中使用libsox来改变声音文件的速度？

Question

我开发了C代码，用Ubuntu使用以下示例代码上的libsox库更改声音文件(3到10秒ogg文件)的速度(增加ogg文件)。使用以下示例代码(值> 1)的得到输出文件(用截断的声音)，但是对于tempo (值< 1)，我得到了正确的输出文件(所有语音示例)。

#include "sox.h"
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>

/*
* Reads input file, applies effects, stores in output file.  
*executable file:example, input fie:audio.ogg ,output file:tempo.ogg 
E.g. ./example audio.ogg tempo.ogg
*/
int main(int argc, char * argv[])
{
static sox_format_t * in, * out; /* input and output files */
sox_effects_chain_t * chain;
sox_effect_t * e;
char * args[10];

assert(argc == 3);

/* All libSoX applications must start by initialising the SoX library    */
assert(sox_init() == SOX_SUCCESS);

/* Open the input file (with default parameters) */
assert(in = sox_open_read(argv[1], NULL, NULL, NULL));

/* Open the output file; we must specify the output signal characteristics.
* Since we are using only simple effects, they are the same as the input
 * file characteristics */
assert(out = sox_open_write(argv[2], &in->signal, NULL, NULL, NULL, NULL));

/* Create an effects chain; some effects need to know about the input
* or output file encoding so we provide that information here */
chain = sox_create_effects_chain(&in->encoding, &out->encoding);

/* The first effect in the effect chain must be something that can source
* samples; in this case, we use the built-in handler that inputs
* data from an audio file */
e = sox_create_effect(sox_find_effect("input"));
args[0] = (char *)in, assert(sox_effect_options(e, 1, args) == SOX_SUCCESS);
/* This becomes the first `effect' in the chain */
assert(sox_add_effect(chain, e, &in->signal, &in->signal) == SOX_SUCCESS);
free(e);

 /* Create the `tempo' effect, and initialise it with the desired parameters: */
e = sox_create_effect(sox_find_effect("tempo"));
args[0] = "1.5", assert(sox_effect_options(e, 1, args) == SOX_SUCCESS);
/* Add the effect to the end of the effects processing chain: */
assert(sox_add_effect(chain, e, &in->signal, &in->signal) == SOX_SUCCESS);
free(e);
/* The last effect in the effect chain must be something that only consumes
* samples; in this case, we use the built-in handler that outputs
* data to an audio file */
e = sox_create_effect(sox_find_effect("output"));
args[0] = (char *)out, assert(sox_effect_options(e, 1, args) == SOX_SUCCESS);
assert(sox_add_effect(chain, e, &in->signal, &in->signal) == SOX_SUCCESS);
free(e);

/* Flow samples through the effects processing chain until EOF is reached */
sox_flow_effects(chain, NULL, NULL);

/* All done; tidy up: */
sox_delete_effects_chain(chain);
sox_close(out);
sox_close(in);
sox_quit();
return 0;
}

在这里，我使用了speed=1.5，并且尝试了所有大于一个的不同值。

Answer 1

这与src/example0.c类似。我认为这个示例中存在一个错误，它将& in ->signal作为对sox_add_effect()的每个调用的两个参数。

我相信这会用效果的输出配置覆盖in配置。

看看src/example6.c以及它如何使用变量interim_signal作为输入和输出信号。

大致如下：

sox_signalinfo_t interm_signal; /* @ intermediate points in the chain. */
...

interm_signal = in->signal; /* NB: deep copy */
...

/* Create the `vol' effect, and initialise it with the desired parameters: */
e = sox_create_effect(sox_find_effect("vol"));
args[0] = "3dB", assert(sox_effect_options(e, 1, args) == SOX_SUCCESS);
/* Add the effect to the end of the effects processing chain: */
assert(sox_add_effect(chain, e, &interm_signal, &out->signal) == SOX_SUCCESS);
free(e);