Implement custom io_open/io_close support in container

Created by: philipnbbc

This PR adds an io_open option to av.open() which allows a client to provide a custom I/O. The io_open function is called with parameters url, flags, and options when a new file needs to be opened.

The existing file I/O was factored out into the PyIOFile class, with the addition of the fclose method. This class is used for the main file as well as for any files opened by the container.

Custom I/O has been used with the FFmpeg DASH encoder and could be used with containers that uses the io_open and io_close callbacks in the AVFormatContext. The test shows how it can be used with the DASH encoder by using a CUSTOM_IO_PROTOCOL prefix to direct the DASH encoder to use the custom I/O.

added changes requested label

mentioned in merge request !918 (closed)

mentioned in merge request !919 (merged)

Why these changes?

Created by: philipnbbc

I've simplified it in https://github.com/PyAV-Org/PyAV/pull/718/commits/cc5b261e80122e46853609bb01f718becf6da26e to just enable libxml2. The DASH demuxer, which is used in the tests, is not enabled if libxml2 is not enabled; libxml2 is used to read the DASH manifest XML file.

Would a test which writes a sequence of PNG files also make sense?

Do by all means keep your DASH test as it gives us a real-life example.

Created by: philipnbbc

I think that would be worth doing (added in https://github.com/PyAV-Org/PyAV/pull/718/commits/d4b23725cb18303bdf809730156889d2c452e92b) and it actually exposed a bug that the DASH muxer hadn't (fixed in https://github.com/PyAV-Org/PyAV/pull/718/commits/d8f096baab46cb470fc78eda5b43ac49a122ceeb).

This io_open argument needs a docstring explaining what the expected signature is, and how to use it.

Created by: philipnbbc

Added in https://github.com/PyAV-Org/PyAV/pull/718/commits/d84cc95b17d8dae6ac2b3329851d00fc7cda0d76

requested review from @jlaine

Merged by: jlaine at 2022-03-31 21:29:02 UTC

closed