ffmpeg基础 -- avio_alloc_context 读内存

转载：https://www.jianshu.com/p/3c95b0471d3a

// 不要用第四个参数传自定的数据，当av_read_frame的时候会出问题，无限循环
avio_ctx = avio_alloc_context(avio_ctx_buffer, avio_ctx_buffer_size, 0, NULL, read_packet, NULL, NULL);

/* 
avio_alloc_context开头会读取部分数据探测流的信息,不会全部读取，除非设置的缓存过大
av_read_frame会在读帧的时候调用avio_alloc_context中的read_packet方法取流数据，每隔avio_ctx_buffer_size调用一次，直至读完
*/

/*正确方式*/
struct buffer_data
{
    uint8_t *ptr; /* 文件中对应位置指针 */
    size_t size;  ///< size left in the buffer /* 文件当前指针到末尾 */
};

// 重点，自定的buffer数据要在外面这里定义
struct buffer_data bd = {0};

//用来将内存buffer的数据拷贝到buf
int read_packet(void *opaque, uint8_t *buf, int buf_size)
{

    buf_size = FFMIN(buf_size, bd.size);

    if (!buf_size)
        return AVERROR_EOF;
    printf("ptr:%p size:%zu bz%zu\n", bd.ptr, bd.size, buf_size);

    /* copy internal buffer data to buf */
    memcpy(buf, bd.ptr, buf_size);
    bd.ptr += buf_size;
    bd.size -= buf_size;

    return buf_size;
}

/* 打开前端传来的视频buffer */
int open_input_buffer(uint8_t *buf, int len)
{
    unsigned char *avio_ctx_buffer = NULL;
    size_t avio_ctx_buffer_size = 32768;
    
    AVInputFormat* in_fmt = av_find_input_format("h265");

    bd.ptr = buf;  /* will be grown as needed by the realloc above */
    bd.size = len; /* no data at this point */

    fmt_ctx = avformat_alloc_context();

    avio_ctx_buffer = (unsigned char *)av_malloc(avio_ctx_buffer_size);
    
    /* 读内存数据 */
    avio_ctx = avio_alloc_context(avio_ctx_buffer, avio_ctx_buffer_size, 0, NULL, read_packet, NULL, NULL);

    fmt_ctx->pb = avio_ctx;
    fmt_ctx->flags = AVFMT_FLAG_CUSTOM_IO;

    /* 打开内存缓存文件, and allocate format context */
    if (avformat_open_input(&fmt_ctx, "", in_fmt, NULL) < 0)
    {
        fprintf(stderr, "Could not open input\n");
        return -1;
    }
    return 0;
}