linesize

linesize说明

#define AV_NUM_DATA_POINTERS 8
/**
 * For video, size in bytes of each picture line.
 * For audio, size in bytes of each plane.
 *
 * For audio, only linesize[0] may be set. For planar audio, each channel
 * plane must be the same size.
 *
 * For video the linesizes should be multiples of the CPUs alignment
 * preference, this is 16 or 32 for modern desktop CPUs.
 * Some code requires such alignment other code can be slower without
 * correct alignment, for yet other it makes no difference.
 *
 * @note The linesize may be larger than the size of usable data -- there
 * may be extra padding present for performance reasons.
 */
int linesize[AV_NUM_DATA_POINTERS];

计算linesize

/**
 * Fill plane linesizes for an image with pixel format pix_fmt and
 * width width.
 *
 * @param linesizes array to be filled with the linesize for each plane
 * @return >= 0 in case of success, a negative error code otherwise
 */
int av_image_fill_linesizes(int linesizes[4], enum AVPixelFormat pix_fmt, int width)
{
    int i, ret;
    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(pix_fmt);
    int max_step     [4];       /* max pixel step for each plane */
    int max_step_comp[4];       /* the component for each plane which has the max pixel step */

    memset(linesizes, 0, 4*sizeof(linesizes[0]));

    if (!desc || desc->flags & AV_PIX_FMT_FLAG_HWACCEL)
        return AVERROR(EINVAL);

    av_image_fill_max_pixsteps(max_step, max_step_comp, desc);
    for (i = 0; i < 4; i++) {
        if ((ret = image_get_linesize(width, i, max_step[i], max_step_comp[i], desc)) < 0)
            return ret;
        linesizes[i] = ret;
    }

    return 0;
}


/**
 * 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;
}