[FFmpeg-devel] [PATCH] Reduce default FDK decoder delay by one frame

[Omer Osman]

Dear members of FFmpeg-devel,


First, I would like to apologize for the approach taken on the license 
modification.


I am working at Fraunhofer IIS department of Audio for Embedded Systems. 
We are actively working on AAC technologies and are the developers of 
the FDK library.
The FDK library has been made publicly available through the Android 
Open Source Project and became available for use outside of Android 
through Martin Storsjö's github repository, and through his 
implementation of libavcodec/libfdk-aac*.c wrapper.

The FDK library itself is actively maintained by us in collaboration 
with Google. As we are the developers of the FDK library, we see that 
FFmpeg can benefit from our contributions, since we are aware of the 
fine implementation details and can provide up-to-date and complete 
wrapper patches as soon the FDK library is updated in the Android Open 
Source Project and at github.

As demonstrated by this patch, using the FDK decoder through FFmpeg 
results in an additional output delay of one frame compared to FFmpeg 
native AAC decoder. For file based decoding, the result of this is that 
the final output file is of the same size, but the last frame ends up 
being "lost".
Additionally, we intend to provide an interface to features that are 
currently not available in this wrapper. This includes Dynamic Range 
Control metadata support, and LOAS decoding (which is currently 
available through the FFmpeg native decoder but not through FFmpeg+FDK).

What is intended by our first patch regarding the license is to provide 
a mechanism for us to be able to maintain this wrapper. We are aware 
that the FFmpeg Development Policy states "Contributions should be 
licensed under LGPL 2.1, including an 'or any later version' clause". 
However, after consulting legal expertise, we have determined that it 
would only be possible for us to contribute to FFmpeg under LGPL v2.1 
only. The FDK library itself is under the 'FDK license' already, 
requiring a build using '--enable-nonfree', and the wrapper is very 
closely tied to the FDK library. Would it thus be possible to accept our 
license change, limited only for this FDK wrapper, in order that we can 
contribute?

We realize that putting this requirement as part of the patch should 
have been done separately from the patch itself, and for this we 
apologize. Clearly, we do not intend to do this without the knowledge of 
the original contributor of this wrapper, as he was put on cc in the 
patch submission.

We wish now to ask how we can proceed.



Best regards,

Omer Osman, M.S.
Realtime Audio Processing
Fraunhofer-Institut für Integrierte Schaltungen IIS
Am Wolfsmantel 33, 91058 Erlangen, DE
Telefon  +49 (0) 9131 / 776-6156
Fax      +49 (0) 9131 / 776-6099
E-Mail   omer.osman at iis.fraunhofer.de
Internet www.iis.fraunhofer.de