ffmpeg: add ability to disable SecureTransport

[saghul]

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It uses private APIs which Apple doesn't allow on AppStore releases.

[zmwangx]

Might be worth checking whether /usr/lib/libssl.0.9.8.dylib is linked when --disable-securetransport is specified. If it is, we might want to add --disable-openssl unless --with-openssl is specified.

[saghul]

@zmwangx TBH I don't know what ffmpeg needs those for. Also, AFAIK --with-openssl is not the default, so why would it link with the system OpenSSL? Also, its header have not been exported for the past 2 macOS releases...

[zmwangx]

TBH I don't know what ffmpeg needs those for.

FFmpeg supports a bunch of streaming protocols — RTMP and RTSP for instance — that may require TLS, among other things.

Also, AFAIK --with-openssl is not the default, so why would it link with the system OpenSSL?

FFmpeg's configure autodetects many optional dependencies. However, I just checked and --enable-openssl defaults to no, so no need to worry about it.

[saghul]

@zmwangx Ok. So, is there anything else I would need to do here?

[zmwangx]

I'm 👍 on this.

[MikeMcQuaid]

Thanks again for your contribution to Homebrew! Without people like you submitting PRs we couldn't run this project. Thanks for the help here too @zmwangx. You rock!