FFmpeg处理过程（代码说明）

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编码环境：ubuntu 麒麟 14.10

FFmpeg默认编译。

在编译自己写的代码时，由于默认路径原因，直接修改源代码中doc/example下面的Makefile文件

头文件如下：

#include <libavcodec/avcodec.h>#include <libavformat/avformat.h>#include <libavformat/avio.h>#include <libavutil/file.h>struct buffer_data {    uint8_t *ptr;    size_t size; ///< size left in the buffer};static int read_packet(void *opaque, uint8_t *buf, int buf_size){    struct buffer_data *bd = (struct buffer_data *)opaque;    buf_size = FFMIN(buf_size, bd->size);    printf("ptr:%p size:%zu\n", bd->ptr, bd->size);    /* copy internal buffer data to buf */    memcpy(buf, bd->ptr, buf_size);    bd->ptr  += buf_size;    bd->size -= buf_size;    return buf_size;}int main(int argc, char *argv[]){    AVFormatContext *fmt_ctx = NULL;    AVIOContext *avio_ctx = NULL;    uint8_t *buffer = NULL, *avio_ctx_buffer = NULL;    size_t buffer_size, avio_ctx_buffer_size = 4096;    char *input_filename = NULL;    int ret = 0;    struct buffer_data bd = { 0 };    if (argc != 2) {        fprintf(stderr, "usage: %s input_file\n"                "API example program to show how to read from a custom buffer "                "accessed through AVIOContext.\n", argv[0]);        return 1;    }    input_filename = argv[1];    /* register codecs and formats and other lavf/lavc components*/    av_register_all();    /* slurp file content into buffer */    ret = av_file_map(input_filename, &buffer, &buffer_size, 0, NULL);    if (ret < 0)        goto end;    /* fill opaque structure used by the AVIOContext read callback */    bd.ptr  = buffer;    bd.size = buffer_size;    if (!(fmt_ctx = avformat_alloc_context())) {        ret = AVERROR(ENOMEM);        goto end;    }    avio_ctx_buffer = av_malloc(avio_ctx_buffer_size);    if (!avio_ctx_buffer) {        ret = AVERROR(ENOMEM);        goto end;    }    avio_ctx = avio_alloc_context(avio_ctx_buffer, avio_ctx_buffer_size,                                  0, &bd, &read_packet, NULL, NULL);    if (!avio_ctx) {        ret = AVERROR(ENOMEM);        goto end;    }    fmt_ctx->pb = avio_ctx;    ret = avformat_open_input(&fmt_ctx, NULL, NULL, NULL);    if (ret < 0) {        fprintf(stderr, "Could not open input\n");        goto end;    }    ret = avformat_find_stream_info(fmt_ctx, NULL);    if (ret < 0) {        fprintf(stderr, "Could not find stream information\n");        goto end;    }    av_dump_format(fmt_ctx, 0, input_filename, 0);end:    avformat_close_input(&fmt_ctx);    /* note: the internal buffer could have changed, and be != avio_ctx_buffer */    if (avio_ctx) {        av_freep(&avio_ctx->buffer);        av_freep(&avio_ctx);    }    av_file_unmap(buffer, buffer_size);    if (ret < 0) {        fprintf(stderr, "Error occurred: %s\n", av_err2str(ret));        return 1;    }    return 0;}

上面的代码为源代码中的一个例子，可以大致看出运行的顺序。

首先注册容器、编码器：

av_register_all();

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