如何使用libavformat而不使用其他libav库？ [英] How can libavformat be used without using other libav libraries?

问题描述

我想要一个使用libavformat到mux视频的简单工作示例。有很好的例子（ doc / examples / muxing.c ），显示编码使用libavcodec，使用libavformat进行复制，并使用libavio保存数据。然而，没有一个例子，我知道它使用libavformat本身，喂入缓冲区中的编码数据，并在缓冲区中获取多路复用数据。

fold：一个，添加一个流 avformat_new_stream（AVFormatContext * s，const AVCodec * c）需要引用编解码器;和两个，muxing的输出被传递给 AVFormatContext-> pb 这是一个 AVIOContext * 。因此，似乎没有（显而易见的）从其他libav库中提取libavformat的方法。

另请参见：此问题提到了一种不使用libavio的方法：从libavformat获取TS数据包到缓冲区

解决方案

您可以避免对libavcodec库的依赖，但您需要头文件（例如avcodec.h）。

方案如下：

  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; 
 
 //填写编解码器上下文所需的属性。 
 // *从文档：
 // *用户设置编解码器信息，muxer将其写入输出。 
 // * AVCodecContext 
 // *文件中指定的必填字段必须设置，即使AVCodecContext是
 // *实际上不用于编码。 
 my_tune_codec（strmCodec）; 
 
 if（oFmtCtx-> oformat-> flags& AVFMT_NOFILE）
 {
 :: avio_open2（& oFmtCtx-> pb，fileName，AVIO_FLAG_WRITE，NULL，空值）; 
} 
 :: avformat_write_header（oFmtCtx，NULL）; 
 // ..... 
 //写循环
 // ..... 
 :: av_write_trailer（oFmtCtx）; 
 :: avio_close（oFmtCtx-> pb）; 
 :: avformat_free_context（oFmtCtx）; 
  

要获得输出，您必须使用 AVIOContext 。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
要创建您自己的 AVIOContext ，您必须执行此操作

  #include< stdio.h> 
 externC{
 #include  #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） 
 
 //使用lseeki64而不是fseek 
 return fseek（h-> f_，static_cast< long>（offset），whichce）; 
} 
 :: 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（）; 
 
 ///使用ctx 
 
 fclose（f）; 
 return 0; 
} 
  

I would like a simple working example of using just libavformat to mux video. There are nice examples (doc/examples/muxing.c) that show encoding with libavcodec, muxing with libavformat and saving the data with libavio. However, there is no example I know of that uses libavformat by itself, feeding in encoded data in a buffer and getting muxed data in a buffer.

The difficulty is two-fold: one, adding a stream with avformat_new_stream(AVFormatContext *s, const AVCodec *c) requires a reference to the codec; and two, the output from muxing is passed to AVFormatContext->pb which is an AVIOContext*. Thus there seems to be no (obvious) way to extricate libavformat from the other libav libraries.

See also: This question mentions a way to not use libavio: Get TS packets into buffer from libavformat

解决方案

You can avoid dependencies on libavcodec library, but you need the header files (for example, avcodec.h).

The scheme is as follows:

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);

To get the output, you always have to use the concept of AVIOContext. You can avoid using the built-in protocols. To do this you need to create your own AVIOContext (::avio_alloc_context).

UPD To create your own AVIOContext, you have to do something like this

#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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