ffmpeg之samplefmt

音频量化格式和相关的工具函数

目录

• 类型说明
  • AVSampleFormat
  • SampleFmtInfo
• 便捷的工具函数
  • av_get_sample_fmt_name
  • av_get_sample_fmt
  • av_get_alt_sample_fmt
  • av_get_packed_sample_fmt
  • av_get_planar_sample_fmt
  • av_get_sample_fmt_string
  • av_get_bytes_per_sample
  • av_sample_fmt_is_planar
  • av_sample_get_buffer_size
  • av_samples_fill_array
  • av_sample_alloc
  • av_samples_alloc_array_and_samples
  • av_samples_copy
  • av_samples_set_slience

类型说明

AVSampleFormat

/**
 * Audio sample formats
 *
 * - The data described by the sample format is always in native-endian order.
 *   Sample values can be expressed by native C types, hence the lack of a signed
 *   24-bit sample format even though it is a common raw audio data format.
 *
 * - The floating-point formats are based on full volume being in the range
 *   [-1.0, 1.0]. Any values outside this range are beyond full volume level.
 *
 * - The data layout as used in av_samples_fill_arrays() and elsewhere in FFmpeg
 *   (such as AVFrame in libavcodec) is as follows:
 *
 * @par
 * For planar sample formats, each audio channel is in a separate data plane,
 * and linesize is the buffer size, in bytes, for a single plane. All data
 * planes must be the same size. For packed sample formats, only the first data
 * plane is used, and samples for each channel are interleaved. In this case,
 * linesize is the buffer size, in bytes, for the 1 plane.
 *
 */
/*
*planar：每个音频数据通道位于不同的plane,且所有plane的数据长度是一致的, data[0] = LLL..., data[1] = RRR...。
*	linesize表示单个plane的buffer size（以字节为单位）。
*packed：仅使用了第一个plane，且数据是交错存储的，data[0] = LRLRLR...。
*	linesize表示单个plane的buffer size（以字节为单位）。。。（仅使用了一个plane == 单个plane）
*/
enum AVSampleFormat {
    AV_SAMPLE_FMT_NONE = -1,
    AV_SAMPLE_FMT_U8,          ///< unsigned 8 bits
    AV_SAMPLE_FMT_S16,         ///< signed 16 bits
    AV_SAMPLE_FMT_S32,         ///< signed 32 bits
    AV_SAMPLE_FMT_FLT,         ///< float
    AV_SAMPLE_FMT_DBL,         ///< double

    AV_SAMPLE_FMT_U8P,         ///< unsigned 8 bits, planar
    AV_SAMPLE_FMT_S16P,        ///< signed 16 bits, planar
    AV_SAMPLE_FMT_S32P,        ///< signed 32 bits, planar
    AV_SAMPLE_FMT_FLTP,        ///< float, planar
    AV_SAMPLE_FMT_DBLP,        ///< double, planar
    AV_SAMPLE_FMT_S64,         ///< signed 64 bits
    AV_SAMPLE_FMT_S64P,        ///< signed 64 bits, planar

    AV_SAMPLE_FMT_NB           ///< Number of sample formats. DO NOT USE if linking dynamically
};

SampleFmtInfo

// 量化格式信息
typedef struct SampleFmtInfo {
    char name[8];       // 量化格式名称
    int bits;                    // bits >> 3 占据字节数量（1byte = 8bit ( 8 == 2 ** 3)）
    int planar;              // 是否为planar格式，1是，0不是
    enum AVSampleFormat altform; ///< planar<->packed alternative form，相反的格式
} SampleFmtInfo;

/** this table gives more information about formats */
// 量化格式参照表
static const SampleFmtInfo sample_fmt_info[AV_SAMPLE_FMT_NB] = {
    [AV_SAMPLE_FMT_U8]   = { .name =   "u8", .bits =  8, .planar = 0, .altform = AV_SAMPLE_FMT_U8P  },
    [AV_SAMPLE_FMT_S16]  = { .name =  "s16", .bits = 16, .planar = 0, .altform = AV_SAMPLE_FMT_S16P },
    [AV_SAMPLE_FMT_S32]  = { .name =  "s32", .bits = 32, .planar = 0, .altform = AV_SAMPLE_FMT_S32P },
    [AV_SAMPLE_FMT_S64]  = { .name =  "s64", .bits = 64, .planar = 0, .altform = AV_SAMPLE_FMT_S64P },
    [AV_SAMPLE_FMT_FLT]  = { .name =  "flt", .bits = 32, .planar = 0, .altform = AV_SAMPLE_FMT_FLTP },
    [AV_SAMPLE_FMT_DBL]  = { .name =  "dbl", .bits = 64, .planar = 0, .altform = AV_SAMPLE_FMT_DBLP },
    [AV_SAMPLE_FMT_U8P]  = { .name =  "u8p", .bits =  8, .planar = 1, .altform = AV_SAMPLE_FMT_U8   },
    [AV_SAMPLE_FMT_S16P] = { .name = "s16p", .bits = 16, .planar = 1, .altform = AV_SAMPLE_FMT_S16  },
    [AV_SAMPLE_FMT_S32P] = { .name = "s32p", .bits = 32, .planar = 1, .altform = AV_SAMPLE_FMT_S32  },
    [AV_SAMPLE_FMT_S64P] = { .name = "s64p", .bits = 64, .planar = 1, .altform = AV_SAMPLE_FMT_S64  },
    [AV_SAMPLE_FMT_FLTP] = { .name = "fltp", .bits = 32, .planar = 1, .altform = AV_SAMPLE_FMT_FLT  },
    [AV_SAMPLE_FMT_DBLP] = { .name = "dblp", .bits = 64, .planar = 1, .altform = AV_SAMPLE_FMT_DBL  },
};

---

便捷的工具函数

av_get_sample_fmt_name

• brief:获取量化格式对应的字符串名称
• parameter: 量化格式
• return: 成功返回量化格式的字符串名称，失败返回NULL

/**
 * Return the name of sample_fmt, or NULL if sample_fmt is not recognized.
 */
const char *av_get_sample_fmt_name(enum AVSampleFormat sample_fmt)
{
    if (sample_fmt < 0 || sample_fmt >= AV_SAMPLE_FMT_NB)
        return NULL;
    return sample_fmt_info[sample_fmt].name;
}

av_get_sample_fmt

• 获取字符串名称对应的量化格式
• parameter: 量化格式的字符串名称
• return：成功返回对应的量化格式，失败返回AV_SAMPLE_FMT_NONE

/**
 * Return a sample format corresponding to name, or AV_SAMPLE_FMT_NONE
 * on error.
 */
enum AVSampleFormat av_get_sample_fmt(const char *name)
{
    int i;

    for (i = 0; i < AV_SAMPLE_FMT_NB; i++)
        if (!strcmp(sample_fmt_info[i].name, name))
            return i;
    return AV_SAMPLE_FMT_NONE;
}

av_get_alt_sample_fmt

• brief：获取相反的量化格式

• parameter：sample_fmt：量化格式，planar：是否为planar格式

• return：失败是返回AV_SAMPLE_FMT_NONE。

  ​ 如果传递的sample_fmt已经采用请求的量化格式，则返回自己sample_fmt，比如 AV_SAMPLE_FMT_S16 = av_get_alt_sample_fmt(AV_SAMPLE_FMT_S16, 0);

  ​ 否则返回对应的量化格式，比如AV_SAMPLE_FMT_S16P = av_get_alt_sample_fmt(AV_SAMPLE_FMT_S16, 1)。

/**
 * Return the planar<->packed alternative form of the given sample format, or
 * AV_SAMPLE_FMT_NONE on error. If the passed sample_fmt is already in the
 * requested planar/packed format, the format returned is the same as the
 * input.
 */
enum AVSampleFormat av_get_alt_sample_fmt(enum AVSampleFormat sample_fmt, int planar)
{
    if (sample_fmt < 0 || sample_fmt >= AV_SAMPLE_FMT_NB)
        return AV_SAMPLE_FMT_NONE;
    if (sample_fmt_info[sample_fmt].planar == planar)
        return sample_fmt;
    return sample_fmt_info[sample_fmt].altform;
}

av_get_packed_sample_fmt

• brief:返回packed格式的量化格式

• parameter：sample_fmt请求的量化格式

• return：失败返回AV_SAMPLE_FMT_NONE；

  ​ 如果输入的已经是packed的格式，则返回自己sample_fmt。

  ​ 否则返回对应的的packed格式的量化格式

/**
 * Get the packed alternative form of the given sample format.
 *
 * If the passed sample_fmt is already in packed format, the format returned is
 * the same as the input.
 *
 * @return  the packed alternative form of the given sample format or
            AV_SAMPLE_FMT_NONE on error.
*/
enum AVSampleFormat av_get_packed_sample_fmt(enum AVSampleFormat sample_fmt)
{
    if (sample_fmt < 0 || sample_fmt >= AV_SAMPLE_FMT_NB)
        return AV_SAMPLE_FMT_NONE;
    if (sample_fmt_info[sample_fmt].planar)
        return sample_fmt_info[sample_fmt].altform;
    return sample_fmt;
}

av_get_planar_sample_fmt

• brief:返回planar格式的量化格式

• parameter：sample_fmt请求的量化格式

• return：失败返回AV_SAMPLE_FMT_NONE；

  ​ 如果输入的已经是planar的格式，则返回自己sample_fmt。

  ​ 否则返回对应的的planar格式的量化格式

/**
 * Get the planar alternative form of the given sample format.
 *
 * If the passed sample_fmt is already in planar format, the format returned is
 * the same as the input.
 *
 * @return  the planar alternative form of the given sample format or
            AV_SAMPLE_FMT_NONE on error.
 */
enum AVSampleFormat av_get_planar_sample_fmt(enum AVSampleFormat sample_fmt)
{
    if (sample_fmt < 0 || sample_fmt >= AV_SAMPLE_FMT_NB)
        return AV_SAMPLE_FMT_NONE;
    if (sample_fmt_info[sample_fmt].planar)
        return sample_fmt;
    return sample_fmt_info[sample_fmt].altform;
}

av_get_sample_fmt_string

• brief:获取指定量化格式的表示字符串，如果sample_fmt小于0,这返回描述信息头
• parameter：buf：描述字符串，buf_size, sample_fmt
• return：量化格式的对应字符串描述

/**
 * Generate a string corresponding to the sample format with
 * sample_fmt, or a header if sample_fmt is negative.
 *
 * @param buf the buffer where to write the string
 * @param buf_size the size of buf
 * @param sample_fmt the number of the sample format to print the
 * corresponding info string, or a negative value to print the
 * corresponding header.
 * @return the pointer to the filled buffer or NULL if sample_fmt is
 * unknown or in case of other errors
 */
char *av_get_sample_fmt_string (char *buf, int buf_size, enum AVSampleFormat sample_fmt)
{
    /* print header */
    if (sample_fmt < 0)
        snprintf(buf, buf_size, "name  " " depth");
    else if (sample_fmt < AV_SAMPLE_FMT_NB) {
        SampleFmtInfo info = sample_fmt_info[sample_fmt];
        snprintf (buf, buf_size, "%-6s" "   %2d ", info.name, info.bits);
    }

    return buf;
}

av_get_bytes_per_sample

• brief:获取指定量化格式的单个样本使用的字节数量
• parameter
• return：如果sample_fmt非法，返回0,成功返回占据字节数量

/**
 * Return number of bytes per sample.
 *
 * @param sample_fmt the sample format
 * @return number of bytes per sample or zero if unknown for the given
 * sample format
 */
int av_get_bytes_per_sample(enum AVSampleFormat sample_fmt)
{
     return sample_fmt < 0 || sample_fmt >= AV_SAMPLE_FMT_NB ?
        0 : sample_fmt_info[sample_fmt].bits >> 3;
}

av_sample_fmt_is_planar

• brief:判断指定量化格式释放为planar格式
• parameter
• return：如果是planar格式则返回1,否则返回0

/**
 * Check if the sample format is planar.
 *
 * @param sample_fmt the sample format to inspect
 * @return 1 if the sample format is planar, 0 if it is interleaved
 */
int av_sample_fmt_is_planar(enum AVSampleFormat sample_fmt)
{
     if (sample_fmt < 0 || sample_fmt >= AV_SAMPLE_FMT_NB)
         return 0;
     return sample_fmt_info[sample_fmt].planar;
}

av_sample_get_buffer_size

• brief：获取指定样本格式的缓冲区大小
• parameter：linesize单个plane的大小，nb_channels声音通道个数，nb_samples:帧率，sample_fmt, align对齐
• return：失败返回负数标示故障码，否则返回缓冲区大小

/**
 * Get the required buffer size for the given audio parameters.
 *
 * @param[out] linesize calculated linesize, may be NULL
 * @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              required buffer size, or negative error code on failure
 */
int av_samples_get_buffer_size(int *linesize, int nb_channels, int nb_samples,
                               enum AVSampleFormat sample_fmt, int align)
{
    int line_size;
    int sample_size = av_get_bytes_per_sample(sample_fmt);
    int planar      = av_sample_fmt_is_planar(sample_fmt);

    /* validate parameter ranges */
    if (!sample_size || nb_samples <= 0 || nb_channels <= 0)
        return AVERROR(EINVAL);

    /* auto-select alignment if not specified */
    if (!align) {
        if (nb_samples > INT_MAX - 31)
            return AVERROR(EINVAL);
        align = 1;
        nb_samples = FFALIGN(nb_samples, 32);
    }

    /* check for integer overflow */
    if (nb_channels > INT_MAX / align ||
        (int64_t)nb_channels * nb_samples > (INT_MAX - (align * nb_channels)) / sample_size)
        return AVERROR(EINVAL);

    line_size = planar ? FFALIGN(nb_samples * sample_size,               align) :
                         FFALIGN(nb_samples * sample_size * nb_channels, align);
    if (linesize)
        *linesize = line_size;

    return planar ? line_size * nb_channels : line_size;
}

av_samples_fill_array

• brief：为指定sample_fmt格式的样本填充plane data和linesize

  ​ 使用char **audio_data接受被填充的样本数据，对于packed数据，仅需要设置audio_data起始点即可，

  ​ 对于planar数据，*audio_data表示不同的通道数据的起点

  ​ linesize：对于planar数据，linesize标示单个plane对齐后的数据大小

  ​ 对于packed数据，linesize标示说有plane对齐后的数据大小总和

  ​ buf的buf_size必须足够大用来存储所有样本，否则audio_data会指向无效数据，可以通过av_samples_get_buffer_size()来计算

• return：指定量化格式需要buf_size

/**
 * 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                 >=0 on success or a negative error code on failure
 * @todo return minimum size in bytes required for the buffer in case
 * of success at the next bump
 */
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 planar to packed
    audio_data[0] = (uint8_t *)buf;
    for (ch = 1; planar && ch < nb_channels; ch++)
        audio_data[ch] = audio_data[ch-1] + line_size;

    if (linesize)
        *linesize = line_size;

    return buf_size;
}

av_sample_alloc

• brief:为指定格式的量化格式分配样本buffer，并且填充静音音频数据
• return：负数标示失败错误码，否则成功

/**
 * Allocate a samples buffer for nb_samples samples, and fill data pointers and
 * linesize accordingly.
 * The allocated samples buffer can be freed by using av_freep(&audio_data[0])
 * Allocated data will be initialized to silence.
 *
 * @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    aligned size for audio buffer(s), may be NULL
 * @param nb_channels      number of audio channels
 * @param nb_samples       number of samples per channel
 * @param align            buffer size alignment (0 = default, 1 = no alignment)
 * @return                 >=0 on success or a negative error code on failure
 * @todo return the size of the allocated buffer in case of success at the next bump
 * @see av_samples_fill_arrays()
 * @see av_samples_alloc_array_and_samples()
 */
int av_samples_alloc(uint8_t **audio_data, int *linesize, int nb_channels,
                     int nb_samples, enum AVSampleFormat sample_fmt, int align)
{
    uint8_t *buf;
    int size = av_samples_get_buffer_size(NULL, nb_channels, nb_samples,
                                          sample_fmt, align);
    if (size < 0)
        return size;

    buf = av_malloc(size);
    if (!buf)
        return AVERROR(ENOMEM);

    size = av_samples_fill_arrays(audio_data, linesize, buf, nb_channels,
                                  nb_samples, sample_fmt, align);
    if (size < 0) {
        av_free(buf);
        return size;
    }

    av_samples_set_silence(audio_data, 0, nb_samples, nb_channels, sample_fmt);

    return size;
}

av_samples_alloc_array_and_samples

• 同av_sample_alloc()

/**
 * Allocate a data pointers array, samples buffer for nb_samples
 * samples, and fill data pointers and linesize accordingly.
 *
 * This is the same as av_samples_alloc(), but also allocates the data
 * pointers array.
 *
 * @see av_samples_alloc()
 */
int av_samples_alloc_array_and_samples(uint8_t ***audio_data, int *linesize, int nb_channels,
                                       int nb_samples, enum AVSampleFormat sample_fmt, int align)
{
    int ret, nb_planes = av_sample_fmt_is_planar(sample_fmt) ? nb_channels : 1;

    *audio_data = av_calloc(nb_planes, sizeof(**audio_data));
    if (!*audio_data)
        return AVERROR(ENOMEM);
    ret = av_samples_alloc(*audio_data, linesize, nb_channels,
                           nb_samples, sample_fmt, align);
    if (ret < 0)
        av_freep(audio_data);
    return ret;
}

av_samples_copy

/**
 * Copy samples from src to dst.
 *
 * @param dst destination array of pointers to data planes
 * @param src source array of pointers to data planes
 * @param dst_offset offset in samples at which the data will be written to dst
 * @param src_offset offset in samples at which the data will be read from src
 * @param nb_samples number of samples to be copied
 * @param nb_channels number of audio channels
 * @param sample_fmt audio sample format
 */
int av_samples_copy(uint8_t **dst, uint8_t * const *src, int dst_offset,
                    int src_offset, int nb_samples, int nb_channels,
                    enum AVSampleFormat sample_fmt)
{
    int planar      = av_sample_fmt_is_planar(sample_fmt);
    int planes      = planar ? nb_channels : 1;
    int block_align = av_get_bytes_per_sample(sample_fmt) * (planar ? 1 : nb_channels);
    int data_size   = nb_samples * block_align;
    int i;

    dst_offset *= block_align;
    src_offset *= block_align;

    if((dst[0] < src[0] ? src[0] - dst[0] : dst[0] - src[0]) >= data_size) {
        for (i = 0; i < planes; i++)
            memcpy(dst[i] + dst_offset, src[i] + src_offset, data_size);
    } else {
        for (i = 0; i < planes; i++)
            memmove(dst[i] + dst_offset, src[i] + src_offset, data_size);
    }

    return 0;
}

av_samples_set_slience

/**
 * Fill an audio buffer with silence.
 *
 * @param audio_data  array of pointers to data planes
 * @param offset      offset in samples at which to start filling
 * @param nb_samples  number of samples to fill
 * @param nb_channels number of audio channels
 * @param sample_fmt  audio sample format
 */
int av_samples_set_silence(uint8_t **audio_data, int offset, int nb_samples,
                           int nb_channels, enum AVSampleFormat sample_fmt)
{
    int planar      = av_sample_fmt_is_planar(sample_fmt);
    int planes      = planar ? nb_channels : 1;
    int block_align = av_get_bytes_per_sample(sample_fmt) * (planar ? 1 : nb_channels);
    int data_size   = nb_samples * block_align;
    int fill_char   = (sample_fmt == AV_SAMPLE_FMT_U8 ||
                     sample_fmt == AV_SAMPLE_FMT_U8P) ? 0x80 : 0x00;
    int i;

    offset *= block_align;

    for (i = 0; i < planes; i++)
        memset(audio_data[i] + offset, fill_char, data_size);

    return 0;
}