音频量化格式和相关的工具函数
类型说明
/**
* 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
};
// 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planar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;
}