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avformat: make avformat_network_init() explicitly optional

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It was sort of optional before - if you didn't call it, networking was
initialized on demand, and an ugly warning was logged. Also, the doxygen
comments threatened that it would be made strictly required one day.

Make it explicitly optional. I would prefer to deprecate it fully, but
there might still be legitimate reasons to use this. But the average
user won't need it.

This is needed only for two reasons: to initialize TLS libraries like
OpenSSL and GnuTLS, and winsock.

OpenSSL and GnuTLS were already silently initialized on demand if the
global network init function was not called. They also have various
thread-safety acrobatics, which make concurrent initialization within
libavformat safe. In addition, the libraries are moving towards making
their global init functions safe, which removes all need for central
global init. In particular, GnuTLS 3.5.16 and OpenSSL 1.1.0g have been
found to have safe init functions. In all cases, they use internal
reference counters to avoid that the global uninit functions interfere
with concurrent uses of the library by other API users who called global
init.

winsock should be thread-safe as well, and maintains an internal
reference counter as well.

Since we still support ancient TLS libraries, which do not have this
fixed, and since it's unknown whether winsock and GnuTLS
reinitialization is costly in any way, don't deprecate the libavformat
functions yet.
This commit is contained in:
wm4
2018-01-16 12:57:04 +01:00
parent 6512ff72f9
commit 631c56a8e4
6 changed files with 20 additions and 19 deletions
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@@ -15,6 +15,12 @@ libavutil: 2017-10-21
API changes, most recent first:
2018-01-xx - xxxxxxx - lavf 58.5.100 - avformat.h
Explicitly make avformat_network_init() and avformat_network_deinit() optional.
If these are not called, network initialization and deinitialization is
automatic, and unlike in older versions, fully supported, unless libavformat
is linked to ancient GnuTLS and OpenSSL.
2018-01-xx - xxxxxxx - lavf 58.4.100 - avformat.h
Deprecate AVStream.recommended_encoder_configuration. It was useful only for
FFserver, which has been removed.