Defined in avio.h

Open a file for input, and or output.

int url_fopen(ByteIOContext *s,
              const char *filename,
              int flags);

ByteIOContext *s

The ByteIOContext to attach the opened file.

const char *filename

The filename to open.

int flags

Open mode, must be one of the url file flags.

Sub zero upon failure.
Is it AVERROR??

url_fclose()

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