Where can I find the source code for gst-discover-1.0, specifically the part where it calculates the duration and extracts metadata information from media files? I want to understand how GStreamer handles this process internally. Any pointers to the relevant files or functions would be greatly appreciated!
It depends on the protocol and the underlying media format.
For file-based formats it will usually be the demuxer who provides that information (in response to a SEEKING query or DURATION query). For elementary stream formats (e.g. mp3, FLAC) it might be the parser instead.
For other media (such as RTSP streams, or HLS/DASH streams) the source elements may be involved.