视频 – 如何在不使用其他libav库的情况下使用libavformat?

我想要一个简单的工作示例,只使用libavformat来复用视频.有很好的例子(doc/examples/muxing.c)用libavcodec显示编码,用libavformat复用并用libavio保存数据.但是,我所知道的没有一个例子就是使用libavformat本身,在缓冲区中输入编码数据并在缓冲区中获取多路复用数据.

困难是双重的:一,用avformat_new_stream(AVFormatContext * s,const AVCodec * c)添加流需要对编解码器的引用;两个,来自多路复用的输出传递给AVFormatContext-> pb,这是一个AVIOContext *.因此,似乎没有(明显的)方法从其他libav库中解放libavformat.

另请参阅:此问题提到了一种不使用libavio的方法:Get TS packets into buffer from libavformat

您可以避免依赖libavcodec库,但需要头文件(例如,avcodec.h).

该计划如下:

AVOutputFormat * oFmt= ::av_guess_format("mp4", NULL, NULL);
AVFormatContext *oFmtCtx = NULL;
::avformat_alloc_output_context2(&oFmtCtx, oFmt, NULL, NULL);
AVStream * oStrm = ::avformat_new_stream(oFmtCtx, NULL);
AVCodecContext * strmCodec = oFmtCtx->streams[0]->codec;

// Fill the required properties for codec context.
// *from the documentation:
// *The user sets codec information, the muxer writes it to the output.
// *Mandatory fields as specified in AVCodecContext
// *documentation must be set even if this AVCodecContext is
// *not actually used for encoding.
my_tune_codec(strmCodec); 

if (oFmtCtx->oformat->flags & AVFMT_NOFILE)
{
  ::avio_open2(&oFmtCtx->pb, fileName, AVIO_FLAG_WRITE, NULL, NULL);
}
::avformat_write_header(oFmtCtx, NULL);
// .....
// writing loop
// .....
::av_write_trailer(oFmtCtx);
::avio_close(oFmtCtx->pb);
::avformat_free_context(oFmtCtx);

要获得输出,您始终必须使用AVIOContext的概念.您可以避免使用内置协议.为此,您需要创建自己的AVIOContext(:: avio_alloc_context).

UPD
要创建自己的AVIOContext,您必须执行以下操作

#include <stdio.h>
extern "C" {
#include <libavformat/avio.h>
#include <libavformat/avformat.h>
}

static const int kBufferSize = 32768;

class my_iocontext_private
{
public:
    my_iocontext_private(FILE * f) : buffer_size_(kBufferSize),
        buffer_(static_cast<unsigned char*>(::av_malloc(buffer_size_))), f_(f) {
        ctx_ = ::avio_alloc_context(buffer_, buffer_size_, AVIO_FLAG_WRITE, this, 
            &my_iocontext_private::read, &my_iocontext_private::write, &my_iocontext_private::seek);
    }

    ~my_iocontext_private()    { av_free(buffer_); }

    static int read(void *opaque, unsigned char *buf, int buf_size) {
        my_iocontext_private* h = static_cast<my_iocontext_private*>(opaque);
        return fread(buf, 1, buf_size, h->f_);
    }

    static int write(void *opaque, unsigned char *buf, int buf_size) {
        my_iocontext_private* h = static_cast<my_iocontext_private*>(opaque);
        return fwrite(buf, 1, buf_size, h->f_);
    }

    static int64_t seek(void *opaque, int64_t offset, int whence) {
        my_iocontext_private* h = static_cast<my_iocontext_private*>(opaque);

        // use lseeki64 instead of fseek
        return fseek(h->f_, static_cast<long>(offset), whence);        
    }
    ::AVIOContext *get_avio() { return ctx_; }

private:
    int buffer_size_;
    unsigned char * buffer_;  
    FILE * f_;
    ::AVIOContext * ctx_;
};

int main(int argc, char* argv[])
{
    FILE * f = fopen("myfile.dmp", "wb");    
    my_iocontext_private priv_ctx(f); 

    AVFormatContext * ctx = ::avformat_alloc_context();
    ctx->pb = priv_ctx.get_avio();

    /// using ctx

    fclose(f); 
    return 0;
}

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