Undefined AVFormatContext duration for custom AVIOContext

Question

The question is why field AVFormatContext::duration is undefined after

avformat_open_input
avformat_find_stream_info

if used custom AVIOContext like in here or here.

With simple file opening, this field is set. Example

Answer 1

The problem was that I not defined seek function so for std::istream example this should be

static int64_t seekFunction(void* opaque, int64_t offset, int whence)
{

auto& stream = *reinterpret_cast<std::istream*>(opaque);

if(whence == AVSEEK_SIZE)
{
    size_t position = stream.tellg();

    stream.seekg(0, std::ios::beg);
    size_t begin = stream.tellg();

    stream.seekg(0, std::ios::end);
    size_t end = stream.tellg();

    stream.seekg(position, std::ios::beg);

    return end - begin;
}

stream.seekg(offset, std::ios::beg);

return stream.tellg();

}

And you should also add clear for clear for stream in readFunction in case of eof