[Libav-user] custom avio_alloc_context and avformat_open_input, how they work.

[Wunna Lwin]

Hi, I am very new to use ffmpeg api. I am reading avio.h File Reference and
implement custom avio_alloc_context but I don't understand the last 4
parameters.
Especially, read_packet and write_packet function callback return integer. I
would like to know where is keeping that return data?

Thanks you very much.