[x264-devel] AVC Intra encoder based on libx264

[Joseph Artsimovich]

On 31/01/2012 18:51, Jason Garrett-Glaser wrote:
> On Tue, Jan 31, 2012 at 2:00 AM, Joseph Artsimovich<joseph at mirriad.com>  wrote:
>> On 31/01/2012 00:42, Jason Garrett-Glaser wrote:
>>> ...
>>>
>>> I've written my own full
>>> implementation, which can be found on my github
>>> (https://github.com/DarkShikari/x264-devel).
>>>
>>> Testing welcome.
>> Will do.  One thing I noticed being missing are custom scaling matrices and
>> i_chroma_qp_offset = 3
> Where in the spec does it list anything about those parameters?
In SMPTE 2027:2011, nowere. Maybe in Panasonic's confidential spec, but 
I don't have access to that. Avid decoder seems to have those hardcoded 
though. Without them, the colours are off in Avid and macroblock 
boundaries are clearly visible. I extracted those from h264 streams 
encoded with Panasonic's encoder.

>> * Need to get rid of a SEI with x264 version info.
> Where in the spec does it prohibit this?  In fact, the spec explicitly
> states that arbitrary SEIs are okay.
The spec doesn't prohibit it. Avid insists on seeing exactly two SEIs 
though.

>> * Need to add two dummy SEIs. Avid decoder will choke if they are missing
>> but doesn't seem to look inside.
> Where in the spec does it say this?  It merely says room must be
> reserved for such SEIs, not how one must reserve them.  In fact, the
> spec explicitly suggests using zero bytes -- not even using NALs!  I
> used a filler NAL because I felt it was less stupid, but either should
> abide by the spec.
If you want my personal opinion, SMPTE 2027:2011 is a joke. Even 
Panasonic's own encoder violates it at one point. Specifically, the spec 
says "Each individual SEI message that may be present shall be a 
multiple of 512 bytes.", while the first SEI produced by Panasonic's 
encoder is shorter than that. In fact, if they didn't put a filler NAL 
in front of it and let the SEI start where the filler starts, it would 
have been exactly 512 bytes.

>> * Frame size is wrong. For 50i, you generate frames of 546000 bytes. It
>> should instead be 559104 + 512*19 =  568832. See my code in avci_encoder.cpp
>> for more details.
> 1.  As far as I can tell from the spec, the 512 SEI bytes are
> *included* in the frame size.  The frame size should be 559,104.
SMPTE 2027:2011 doesn't say if it's included or not, so it's logical to 
assume it is. However, Panasonic's encoder produces frames of 568832 
bytes, which indicates it's not.

> 2.  The code requests a frame size of 559,104, not 546,000.  If you
> can show me a case where it generates the wrong frame size, please do
> so, but I tested a number of resolution/fps combinations and they
> worked correctly.
Sorry, got it wrong. Your frames are indeed 559104 bytes. That's still 
not what Panasonic's (and all other) encoders are producing.

-- 
Joseph Artsimovich
Senior C++ Applications Developer
MirriAd Ltd