[Ffmpeg-devel] Native H.264 encoder

[Michael Niedermayer]

Hi

On Thu, Jan 18, 2007 at 01:07:03PM +0100, Panagiotis Issaris wrote:
> Hi,
> 
> On Mon, 2006-12-18 at 22:04 +0100, Michael Niedermayer wrote:
> > Hi
> > 
> > On Fri, Dec 15, 2006 at 11:34:37PM +0100, Panagiotis Issaris wrote:
> > [...]
> > > > > It
> > > > > seems most codecs reuse parts of MpegEncContext code combined with some
> > > > > conditional parts added to mpegvideo.c. I would prefer to see the motion
> > > > > estimation code separated from the codecs,
> > > > In snow.c, I found the following comment at line 471:
> > > >     MpegEncContext m; // needed for motion estimation, should not be
> > > > used for anything else, the idea is to make the motion estimation
> > > > eventually independant of MpegEncContext, so this will be removed then
> > > > (FIXME/XXX)
> > > Yep, I saw that comment too, but if I recall correctly, it has been there for
> > > quiet a while :)
> > > 
> > > > Since it seems that making the motion estimation codec independant of
> > > > MpegEncContext is in the plans (and can be useful for the whole ffmpeg
> > > > project), I'll try to have a better look to see how to do this (as soon
> > > > as I'll have some time :)...
> > > > I do not promise anything, but I'll try.
> > > Ah! That would be awesome! :) I'll help out whereever I can!
> > 
> > btw 2 tips
> > 1. submit small patches, a 40k motion estimation cleanup patch would be
> >    a nightmare for me and whoever submits it ...
> > 2. look at snow.c and try to reduce the number of lines of code which
> > depend on MpegEncContext if it reaches 0 then motion estimation can be
> > used without MpegEncContext ...
> I've been looking at a way to do this, and started by looking for each
> access of the MpegEncContext field in the SnowContext struct.
> 
> 
> in encode_q_branch():
> MotionEstContext *c= &s->m.me;
> s->m.mb_stride=2;
> s->m.mb_x=
> s->m.mb_y= 0;
> s->m.me.skip= 0;
> c->current_mv_penalty= c->mv_penalty[s->m.f_code=1] + MAX_MV;
> ref_score= s->m.me.sub_motion_search(&s->m, &ref_mx, &ref_my, ref_score,
> 0, 0, level-LOG2_MB_SIZE+4, block_w)
> c->scene_change_score+= s->m.qscale;
> 
> 
> in get_dc():
> DWTELEM *dst= (DWTELEM*)s->m.obmc_scratchpad +
> plane_index*block_size*block_size*4;
> 
> 
> in get_block_rd():
> DWTELEM *pred= (DWTELEM*)s->m.obmc_scratchpad +
> plane_index*block_size*block_size*4;
> 
> 
> in ratecontrol_1pass():
> s->m.current_picture.mb_var_sum= coef_sum;
> s->m.current_picture.mc_mb_var_sum= 0;
> s->m.current_picture.mc_mb_var_sum= coef_sum;
> s->m.current_picture.mb_var_sum= 0;
> 
> 
> in encode_init():
> s->m.avctx   = avctx;
> s->m.flags   = avctx->flags;
> s->m.bit_rate= avctx->bit_rate;
> s->m.me.scratchpad= av_mallocz((avctx->width
> +64)*2*16*2*sizeof(uint8_t));
> s->m.me.map       = av_mallocz(ME_MAP_SIZE*sizeof(uint32_t));
> s->m.me.score_map = av_mallocz(ME_MAP_SIZE*sizeof(uint32_t));
> s->m.obmc_scratchpad= av_mallocz(MB_SIZE*MB_SIZE*12*sizeof(uint32_t));
> 
> 
> in encode_frame():
> s->m.picture_number= avctx->frame_number;
> s->m.pict_type = pict->pict_type=
> s->m.rc_context.entry[avctx->frame_number].new_pict_type;
> s->m.pict_type= pict->pict_type= s->keyframe ? FF_I_TYPE : FF_P_TYPE;
> s->m.current_picture_ptr= &s->m.current_picture;
> s->m.avctx= s->avctx;
> s->m.current_picture.data[0]= s->current_picture.data[0];
> s->m.   last_picture.data[0]= s->last_picture[0].data[0];
> s->m.    new_picture.data[0]= s->  input_picture.data[0];
> s->m.   last_picture_ptr= &s->m.   last_picture;
> s->m.linesize=
> s->m.   last_picture.linesize[0]=
> s->m.    new_picture.linesize[0]=
> s->m.current_picture.linesize[0]= stride;
> s->m.uvlinesize= s->current_picture.linesize[1];
> s->m.width = width;
> s->m.height= height;
> s->m.mb_width = block_width;
> s->m.mb_height= block_height;
> s->m.mb_stride=   s->m.mb_width+1;
> s->m.b8_stride= 2*s->m.mb_width+1;
> s->m.f_code=1;
> s->m.pict_type= pict->pict_type;
> s->m.me_method= s->avctx->me_method;
> s->m.me.scene_change_score=0;
> s->m.flags= s->avctx->flags;
> s->m.quarter_sample= (s->avctx->flags & CODEC_FLAG_QPEL)!=0;
> s->m.out_format= FMT_H263;
> s->m.unrestricted_mv= 1;
> s->m.lambda = s->lambda;
> s->m.qscale= (s->m.lambda*139 + FF_LAMBDA_SCALE*64) >> (FF_LAMBDA_SHIFT
> + 7);
> s->lambda2= s->m.lambda2= (s->m.lambda*s->m.lambda + FF_LAMBDA_SCALE/2)
> >> FF_LAMBDA_SHIFT;
> s->m.dsp= s->dsp; //move
> ff_init_me(&s->m);
> s->dsp= s->m.dsp;
> s->m.pict_type = pict->pict_type;
> s->m.misc_bits = 8*(s->c.bytestream - s->c.bytestream_start);
> s->m.mv_bits = 8*(s->c.bytestream - s->c.bytestream_start) -
> s->m.misc_bits;
> ... && s->m.me.scene_change_score > s->avctx->scenechange_threshold){
> s->m.frame_bits = 8*(s->c.bytestream - s->c.bytestream_start);
> s->m.p_tex_bits = s->m.frame_bits - s->m.misc_bits - s->m.mv_bits;
> s->m.current_picture.display_picture_number =
> s->m.current_picture.coded_picture_number = avctx->frame_number;
> s->m.current_picture.quality = pict->quality;
> s->m.total_bits += 8*(s->c.bytestream - s->c.bytestream_start);
> if(s->pass1_rc)
>     if (ff_rate_estimate_qscale(&s->m, 0) < 0)
>         return -1;
> if(avctx->flags&CODEC_FLAG_PASS1)
>     ff_write_pass1_stats(&s->m);
> s->m.last_pict_type = s->m.pict_type;
> avctx->frame_bits = s->m.frame_bits;
> avctx->mv_bits = s->m.mv_bits;
> avctx->misc_bits = s->m.misc_bits;
> avctx->p_tex_bits = s->m.p_tex_bits;
> 
> 
> in common_end()
> av_freep(&s->m.me.scratchpad);
> av_freep(&s->m.me.map);
> av_freep(&s->m.me.score_map);
> av_freep(&s->m.obmc_scratchpad);
> 
> 
> 
> Afterwards, I filtered out all references to members of the embedded
> MotionEstContext and came to this list:
> avctx, b8_stride, bit_rate, current_picture, current_picture_ptr, dsp,
> f_code, flags, frame_bits, height, lambda, lambda2, last_picture,
> last_picture_ptr, linesize, mb_height, mb_stride, mb_width, mb_x, mb_y,
> me, me_method, misc_bits, mv_bits, new_picture, obmc_scratchpad,
> out_format, pict_type, picture_number, p_tex_bits, qscale,
> quarter_sample, rc_context, total_bits, unrestricted_mv, uvlinesize,
> width

some of these are just needed for the ratecontrol but not ME i think ...


> 
> 
> Some of these fields are also available in SnowContext and are mostly
> likely assigned to the equivalently named fields in the MpegEncContext
> only to get motion estimation working:
> avctx, dsp, new_picture, current_picture, last_picture, lambda, lambda2,
> b_width (==mb_width?), b_height (==mb_height?)
> 
> So, the MotionEstContext apparently does not provide enough contextual
> data for the motion estimation functions and therefore they need access
> to the encompassing MpegEncContext. Would that be a good part to focus
> on first? I'd guess one way to solve this would be to move the required
> fields into the MotionEstContext, or another way would be to pass the
> required field in the relevant function calls of the motion estimation
> functions. Both would require quite a lot of changes as the
> encode_frame() functions accesses quite a lot of MpegEncContext fields. 

yes


> 
> Or should a new indepent context be created, that is not specific to
> mpeg (and related codecs) encoding but contains enough info to allow
> motion estimation? But, ... I'd guess the result would be nearly the
> same as moving all the needed stuff to MotionEstContext, right?

thats an option too, but one very important thing is that the context
can be accessed without an additional pointer dereference (like AVFrame)
what i mean is that the common variables like width/height/... could
be in a common context which is at the begin of MotionEstContext and
MotionEstContext is part of MpegEncContext and SnowContext
no variable duplications and fast access but probably more work then
simply duplicating variables in MotionEstContext and copying them
over during init ...

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato
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