av_samples_fill_arrays

av_samples_fill_arrays是FFmpeg中一个非常重要的函数，用于填充音频数据的指针数组。在音视频处理中，经常需要处理音频数据，而av_samples_fill_arrays可以正确地组织音频数据，以便后续处理和编解码。

av_samples_fill_arrays函数的原型：

/**
 * Fill plane data pointers and linesize for samples with sample
 * format sample_fmt.
 *
 * The audio_data array is filled with the pointers to the samples data planes:
 * for planar, set the start point of each channel's data within the buffer,
 * for packed, set the start point of the entire buffer only.
 *
 * The value pointed to by linesize is set to the aligned size of each
 * channel's data buffer for planar layout, or to the aligned size of the
 * buffer for all channels for packed layout.
 *
 * The buffer in buf must be big enough to contain all the samples
 * (use av_samples_get_buffer_size() to compute its minimum size),
 * otherwise the audio_data pointers will point to invalid data.
 *
 * @see enum AVSampleFormat
 * The documentation for AVSampleFormat describes the data layout.
 *
 * @param[out] audio_data  array to be filled with the pointer for each channel
 * @param[out] linesize    calculated linesize, may be NULL
 * @param buf              the pointer to a buffer containing the samples
 * @param nb_channels      the number of channels
 * @param nb_samples       the number of samples in a single channel
 * @param sample_fmt       the sample format
 * @param align            buffer size alignment (0 = default, 1 = no alignment)
 * @return                 minimum size in bytes required for the buffer on success,
 *                         or a negative error code on failure
 */
int av_samples_fill_arrays(uint8_t **audio_data, int *linesize,
                           const uint8_t *buf,
                           int nb_channels, int nb_samples,
                           enum AVSampleFormat sample_fmt, int align)
{
    int ch, planar, buf_size, line_size;

    planar   = av_sample_fmt_is_planar(sample_fmt);
    buf_size = av_samples_get_buffer_size(&line_size, nb_channels, nb_samples,
                                          sample_fmt, align);
    if (buf_size < 0)
        return buf_size;

    if (linesize)
        *linesize = line_size;

    memset(audio_data, 0, planar
                          ? sizeof(*audio_data) * nb_channels
                          : sizeof(*audio_data));

    if (!buf)
        return buf_size;

    audio_data[0] = (uint8_t *)buf;
    for (ch = 1; planar && ch < nb_channels; ch++)
        audio_data[ch] = audio_data[ch-1] + line_size;

    return buf_size;
}

参数解释：

• audio_data：指向一个指针数组，用于存储音频数据的指针。/AVFrame.data/
• linesize：存储每个音频数据指针的大小。/AVFrame.linesize/
• buf：指向包含音频数据的缓冲区。
• nb_channels：音频通道数。/AVFrame.channels/
• nb_samples：每个通道的样本数。/AVFrame.nb_samples/
• sample_fmt：音频样本格式。/AVFrame.format/
• align：对齐方式。

正确使用av_samples_fill_arrays函数的关键在于正确理解参数的含义和传入正确的参数值。以下是一个简单的示例代码，演示如何使用av_samples_fill_arrays函数：

#include <libavutil/samplefmt.h>
#include <libavutil/mem.h>
#include <libavutil/opt.h>

void fill_audio_data(uint8_t **audio_data, int *linesize, uint8_t *buf, int nb_channels, int nb_samples, enum AVSampleFormat sample_fmt) {
    int ret = av_samples_fill_arrays(audio_data, linesize, buf, nb_channels, nb_samples, sample_fmt, 0);
    if (ret < 0) {
        // 错误处理
        printf("Error filling audio data arrays\n");
    }
}

int main() {
    int nb_samples = 1024;
    int nb_channels = 2;
    enum AVSampleFormat sample_fmt = AV_SAMPLE_FMT_FLTP;
    uint8_t *buf = (uint8_t *)av_malloc(av_samples_get_buffer_size(NULL, nb_channels, nb_samples, sample_fmt, 1));
    uint8_t *audio_data[8]; // 假设最多支持8个通道
    int linesize[8];

    fill_audio_data(audio_data, linesize, buf, nb_channels, nb_samples, sample_fmt);

    // 使用填充好的音频数据进行后续处理

    av_free(buf);
    return 0;
}

在这段示例代码中，首先分配了一个足够大的缓冲区用于存储音频数据，然后调用fill_audio_data函数填充音频数据指针数组。最后可以使用填充好的音频数据进行后续的音频处理操作。