[FFmpeg-devel] [RFC] Error concealment for B-frames/fixing issue 824

Michael Niedermayer michaelni
Fri May 15 03:55:28 CEST 2009


On Thu, May 14, 2009 at 06:03:54PM -0700, Baptiste Coudurier wrote:
> Michael Niedermayer wrote:
> > On Thu, May 14, 2009 at 04:10:30PM -0700, Baptiste Coudurier wrote:
> >> Hi Michael,
> >>
> >> Michael Niedermayer wrote:
> >>> On Thu, May 14, 2009 at 01:42:33PM -0700, Baptiste Coudurier wrote:
> >>>> Baptiste Coudurier wrote:
> >>>>> On 5/5/2009 8:34 PM, Michael Niedermayer wrote:
> >>>>>> On Tue, May 05, 2009 at 07:56:39PM -0700, Baptiste Coudurier wrote:
> >>>>>>> On 5/5/2009 5:17 PM, Michael Niedermayer wrote:
> >>>>>>>> On Tue, May 05, 2009 at 02:08:33PM -0700, Baptiste Coudurier wrote:
> >>>>>>>>> Baptiste Coudurier wrote:
> >>>>>>>>>> On Fri, Apr 10, 2009 at 06:50:08PM -0700, Baptiste Coudurier wrote:
> >>>>>>>>>>> Hi Reimar,
> >>>>>>>>>>>
> >>>>>>>>>>> On 4/9/2009 3:13 PM, Reimar D?ffinger wrote:
> >>>>>>>>>>>> On Thu, Apr 09, 2009 at 10:52:32PM +0200, Michael Niedermayer wrote:
> >>>>>>>>>>>>> there are 2 very seperate things
> >>>>>>>>>>>>> 1. errors
> >>>>>>>>>>>>> 2. b frames without reference frames after seeking
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> normal users dont want to see randomly trashed frames after seeking
> >>>>>>>>>>>>> in undamged files
> >>>>>>>>>>>> I think I agree... Is there a counter somewhere that could be used to
> >>>>>>>>>>>> find out which frame in the GOP we are at?
> >>>>>>>>>>> Yes temp_ref in pic structure.
> >>>>>>>>>>>
> >>>>>>>>>>>> Some options I can think of:
> >>>>>>>>>>>> 1) change code to not skip a B-frame if it is the second frame in a closed GOP
> >>>>>>>>>>>> 2) only skip B-frames if they directly follow the first I-frame of a non-closed GOP
> >>>>>>>>>>>> 3) (without really knowing what "broken link" means) only skip B-frames if "broken
> >>>>>>>>>>>> link" is set
> >>>>>>>>>>> From what I understand, broken link explicitly state that the 2 next b
> >>>>>>>>>>> frames cannot be decoded because the stream was cut at the preceding I
> >>>>>>>>>>> frame, therefore the original reference I frame is no more available.
> >>>>>>>>>>>
> >>>>>>>>>>> And I think your strategy should be ok :)
> >>>>>>>>>> Here is another attempt.
> >>>>>>>>>>
> >>>>>>>>>> It will decodes them only is closed gop is set.
> >>>>>>>>>> I got a sample with open gop and B frames before the I frame, it
> >>>>>>>>>> works, also, decoding them anyway does not crash when dummy picture is
> >>>>>>>>>> allocated some block are gray.
> >>>>>>>>>>
> >>>>>>>>>> Patch attached.
> >>>>>>>>>>
> >>>>>>>>> New patch attached, more correct.
> >>>>>>>> looks ok
> >>>>>>> I've tested it more to be sure and I've encountered this problem during
> >>>>>>> seeking with ffplay:
> >>>>>>>
> >>>>>>> [mpeg2video @ 0x223f6a0]pic->data[0]!=NULL in avcodec_default_get_buffer
> >>>>>>> [mpeg2video @ 0x223f6a0]get_buffer() failed (-1 2147483647 8 0x3269950)
> >>>>>>> [mpeg2video @ 0x223f6a0]pic->data[0]!=NULL in avcodec_default_get_buffer
> >>>>>>> [mpeg2video @ 0x223f6a0]get_buffer() failed (-1 2147483647 8 0x3269950)
> >>>>>>> Seek to 63% ( 0:01:23) of total duration ( 0:02:12)
> >>>>>>> [mpeg2video @ 0x223f6a0]pic->data[0]!=NULL in avcodec_default_get_buffer
> >>>>>>> [mpeg2video @ 0x223f6a0]get_buffer() failed (-1 2147483647 8 0x3140e30)
> >>>>>>> [mpeg2video @ 0x223f6a0]pic->data[0]!=NULL in avcodec_default_get_buffer
> >>>>>>> [mpeg2video @ 0x223f6a0]get_buffer() failed (-1 2147483647 8 0x3140e30)
> >>>>>>>
> >>>>>>> So I guess allocating last_picture this way was not correct.
> >>> likely, yes
> >>>
> >>>
> >>>>>>> I think copying next picture to last picture is better then.
> >>>>>> i dont mind the picture being copied (pixel wise) but having
> >>>>>> s2->last_picture_ptr == s2->next_picture_ptr
> >>>>>> gives me a bad feeling, this is not a conditiom that could be true otherwise
> >>>>> Ok. It seems copying and not setting last_picture_ptr to
> >>>>> next_picture_ptr does not work and crashes. So I feel going to back to
> >>>>> first solution and finding where to correctly free the pic. Any hint ?
> >>>>>
> >>> [...]
> >>>
> >>>> int MPV_frame_start(MpegEncContext *s, AVCodecContext *avctx)
> >>>> {
> >>>>     int i;
> >>>>     AVFrame *pic;
> >>>>     s->mb_skipped = 0;
> >>>>
> >>>>     assert(s->last_picture_ptr==NULL || s->out_format != FMT_H264 ||
> >>>> s->codec_id == CODEC_ID_SVQ3);
> >>>>
> >>>>     /* mark&release old frames */
> >>>>     if (s->pict_type != FF_B_TYPE && s->last_picture_ptr &&
> >>>> s->last_picture_ptr != s->next_picture_ptr &&
> >>>> s->last_picture_ptr->data[0]) {
> >>>>       if(s->out_format != FMT_H264 || s->codec_id == CODEC_ID_SVQ3){
> >>>>           free_frame_buffer(s, s->last_picture_ptr);
> >>>>
> >>>> Does this check implies that in some situation, last_picture_ptr might
> >>>> be next_picture_ptr ?
> >>> yes but not for mpeg1/2 nor any other codec supporting B frames _IIRC_
> >> All right, thanks for the information.
> >>
> >>>> In this case, is it so wrong to set it so for the
> >>>> closed gop case ?
> >>> putting the picture buffers into a state that was not possible previously
> >>> requires the one doing it to fully understand the code in question.
> >>> Someone fully understanding the code should have no problem simply allocating
> >>> a new picture in last_picture* instead of setting it to next_picture_ptr.
> >>>
> >>> summary being, i am not against setting them equal, what iam against is this
> >>> kind of
> >>> first try, hmm it crashes, no faint clue why, lets try something else random,
> >>> ahh doesnt crash, lets submit and let michael figure out if its ok, and if
> >>> it breaks something let michael fix it later ...
> >> Yes, of course, I did not imply this, sorry if I appeared that way.
> >>
> >>> thus given these circumtances i prefer(ed) that the buffers are kept in
> >>> the normal state with next != last
> >> No problem, I'm just now trying to better understand the situation
> >> according to the code, like you are suggesting.
> >>
> >> Situation is: if alloc_frame is used, tracking the buffers and free them
> >> is needed.
> > 
> > what about ff_find_unused_picture() / alloc_picture()
> > ?
> 
> Ahhhhh, here it is :)
> 
> >> If next_picture_ptr is copied, but last_picture_ptr not set to the same
> >> value, it avoids allocation. However it seems the frame will be freed in
> >> free_frame_buffer later while pic->type will be FF_BUFFER_TYPE_COPY.
> > 
> > i dont think it would be FF_BUFFER_TYPE_COPY ?
> > last_picture may but last_picture_ptr should not i think but its all a
> > while ago since i wrote that code
> > that last/next should always be copies of the _ptr versions, the _ptr
> > should not point to last/next
> 
> Yes, it seems allocating &s2->last_picture directly was very wrong.
> 
> Updated patch attached.

isnt that missing code to reset closed_gop in a few cases like
seeking?

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

When you are offended at any man's fault, turn to yourself and study your
own failings. Then you will forget your anger. -- Epictetus
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