[vlc-devel] Append metadata to block_t

[Vladimir Davydov]

Hello dear VLC developers,

I'm trying to implement playback of DASH streams protected by Widevine DRM on 
Android.
I have added Sample Encryption Box ('senc') parsing to MP4 demuxer module.
So, after parsing, I have some encryption info (AES Initial Vector and etc) 
for each media sample. 
I need to somehow pass this crypto info to mediacodec module with media sample 
data.
Original implementation sends media sample in block_t structure. This 
structure has some metadata like i_flags but doesn't have any special storage 
for more big metadata like Initial Vectors.

I have analyzed the code of other modules but didn't find good solution.
What is the usual way to resolve problem like this? 

One of the ways I see is to append metadata at the begin of p_buffer (before 
media sample payload) and set some new flag to i_flags.  But it requires 
adding of new global flag like BLOCK_FLAG_CENC_ENCRYPTED. 
Something like adding to vlc_block.h :
#define BLOCK_FLAG_CENC_ENCRYPTED 0x4000
That is not good because flags range is pretty limited.

Do you have any better ideas to implement it?

Best regards,
Vladimir