[FFmpeg-devel] Would a crypto file be acceptable?

[Mark Gaiser <markg85@gmail.com>]

Hi,

The ffmpeg crypto protocol handler [1] allows one to play encrypted media.

The great thing here is that it allows playback of any media format that
ffmpeg supports!
Have a container format like mkv as an encrypted blob, no problem for the
crypto plugin!

I'm explicitly mentioning mkv (though there's many more) here because that
isn't possible in HLS/MPD. While those streaming formats handle encryption
too, they are very limited in terms of supported codecs and containers.

Playback of encrypted data works like this:
ffplay encrypted_file -decryption_key $AES_KEY -decryption_iv $AES_IV

While this works just fine, it's limited in use because the cryptography
details have to be passed on the command line. Applications that might well
support much of ffmpeg functionality can't easily hook into the crypto
functionality. Take KODI for example, it allows playback of many of the
formats ffmpeg supports but anything with crypto just isn't possible. In
fact, anything that requires custom command line arguments isn't possible.
[2]

My idea is to make a new file format that would be implemented and specced
within [1]. My proposed format would be:

---
CRYPTO-VERSION:1
CRYPTO-KEY:URI:.....
CRYPTO-IV:URI:.....
encrypted_file
---

The URI would be a format type identifier where you can choose between URI
(to pass a URL to a key blob), BASE64URL (key encoded as base64url) or HEX.

The above proposed format should be stored in a file with ".crypto" as
extension. The crypto plugin [1] would then handle that file. The arguments
would be filled based on the "properties" in the file. So for example the
`decryption_key` argument would be populated with the blob returned from
CRYPTO-KEY:URI:<url>. Or with one of the other types.

The "encrypted_file" would just be passed through ffmpeg's
"ffurl_open_whitelist" like the crypto plugin currently does. Meaning that
the file could be anything ffmpeg supports.

Playing encrypted media would be as simple as:
ffplay file.crypto

With this mail I'm looking for a confirmation if the above concept would be
allowed as a patch for ffmpeg? And if not, how can I achieve the same
results in a way that would be acceptable? [3]

Best regards,
Mark Gaiser

[1] https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/crypto.c
[2] there are plugins to make it possible but then you have the extra
requirement of a plugin
[]3 No, not HLS/MPD! They serve a different purpose. Extending them to
serve my purpose is a lost goal to begin with so let's not even go there.
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