FFmpeg encapsulates special tool classes for the acquisition and processing of audio sample formats. Audio sample format enumeration types and related APIs, located in samplefmt.h of the libavutil module, including obtaining the sample format name, obtaining the sample format type, obtaining the bytes occupied by each sample, obtaining the buffer size required for the number of samples, and filling the sample array , allocate sample buffer, copy sample data, fill sample data to mute.
1 、 AVSampleFormat
AVSampleFormat is an enumeration type of audio sampling format, divided into signed and unsigned according to symbol type, 8-bit, 16-bit, 32-bit, 64-bit according to storage number, and int, short, float, double, divided into packed and planar according to the storage structure. details as follows:
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
};2 、 av_get_sample_fmt_name
Get the sample format name and return the name corresponding to the AVSampleFormat enumeration. There is corresponding SampleFmtInfo in samplefmt.c, including fields such as name, bits, planar, and altform:
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 },
};3 、 av_get_sample_fmt
Get the sample format type and return the type corresponding to the AVSampleFormat enumeration.
4 、 av_get_alt_sample_fmt
Returns the optional sample format type of planar or packed, or AV_SAMPLE_FMT_NONE on error.
5、av_get_packed_sample_fmt
Gets the sample format for interleaved storage, returning the type of the AVSampleFormat enumeration.
6 、 av_get_planar_sample_fmt
Get the sample format of the flat storage, returning the type of the AVSampleFormat enumeration.
7 、 of_get_bytes_per_sample
Get the number of bytes occupied by each sample based on the sample format.
8 、 av_sample_fmt_is_planar
Determine whether the sampling format is flat storage.
9、av_samples_get_buffer_size
The buffer size required to obtain the number of samples, the code implementation is located in samplefmt.c, as follows:
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);
// 检查参数是否合法
if (!sample_size || nb_samples <= 0 || nb_channels <= 0)
return AVERROR(EINVAL);
// 如果没有指定，自动选择是否对齐
if (!align) {
if (nb_samples > INT_MAX - 31)
return AVERROR(EINVAL);
align = 1;
nb_samples = FFALIGN(nb_samples, 32);
}
// 检查integer是否溢出
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;
}10、av_samples_fill_arrays
Fill the array according to the number of samples. For planar storage, the buffer of each channel is set with a pointer head; for packed interleaved storage, only one pointer head is set for the entire buffer:
/**
* 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);11 、 av_samples_alloc
Allocate a sample buffer for the number of samples specified by nb_samples.
12 、 av_samples_copy
Copy the sample data from the source address to the destination address.
13 、 av_samples_set_silence
Fill the sample data with mute, if it is AV_SAMPLE_FMT_U8 or AV_SAMPLE_FMT_U8P type, fill with 0x80, otherwise fill with 0x00 uniformly. code show as below:
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;
}