How can libavformat be used without using other libav libraries?
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
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;
}