[FFmpeg-devel] [PATCH 2/4] h264dec: be more explicit in handling container cropping

[Michael Niedermayer]

On Wed, May 10, 2017 at 10:41:30AM -0300, James Almer wrote:
> On 5/9/2017 11:56 PM, Michael Niedermayer wrote:
> > On Mon, May 08, 2017 at 03:46:23PM -0300, James Almer wrote:
> >> From: Anton Khirnov <anton at khirnov.net>
> >>
> >> The current condition can trigger in cases where it shouldn't, with
> >> unexpected results.
> >> Make sure that:
> >> - container cropping is really based on the original dimensions from the
> >>   caller
> >> - those dimenions are discarded on size change
> >>
> >> The code is still quite hacky and eventually should be deprecated and
> >> removed, with the decision about which cropping is used delegated to the
> >> caller.
> >> ---
> >> This merges commit 4fded0480f20f4d7ca5e776a85574de34dfead14 from libav
> >>
> >>  libavcodec/h264_slice.c | 20 +++++++++++++-------
> >>  libavcodec/h264dec.c    |  3 +++
> >>  libavcodec/h264dec.h    |  5 +++++
> >>  3 files changed, 21 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/libavcodec/h264_slice.c b/libavcodec/h264_slice.c
> >> index acf6a73f60..a7916e09ce 100644
> >> --- a/libavcodec/h264_slice.c
> >> +++ b/libavcodec/h264_slice.c
> >> @@ -378,6 +378,8 @@ int ff_h264_update_thread_context(AVCodecContext *dst,
> >>      h->avctx->coded_width   = h1->avctx->coded_width;
> >>      h->avctx->width         = h1->avctx->width;
> >>      h->avctx->height        = h1->avctx->height;
> >> +    h->width_from_caller    = h1->width_from_caller;
> >> +    h->height_from_caller   = h1->height_from_caller;
> >>      h->coded_picture_number = h1->coded_picture_number;
> >>      h->first_field          = h1->first_field;
> >>      h->picture_structure    = h1->picture_structure;
> > 
> >> @@ -874,13 +876,17 @@ static int init_dimensions(H264Context *h)
> >>      av_assert0(sps->crop_top + sps->crop_bottom < (unsigned)h->height);
> >>  
> >>      /* handle container cropping */
> >> -    if (FFALIGN(h->avctx->width,  16) == FFALIGN(width,  16) &&
> >> -        FFALIGN(h->avctx->height, 16) == FFALIGN(height, 16) &&
> >> -        h->avctx->width  <= width &&
> >> -        h->avctx->height <= height
> >> -    ) {
> >> -        width  = h->avctx->width;
> >> -        height = h->avctx->height;
> >> +    if (h->width_from_caller > 0 && h->height_from_caller > 0     &&
> >> +        !sps->crop_top && !sps->crop_left                         &&
> >> +        FFALIGN(h->width_from_caller,  16) == FFALIGN(width,  16) &&
> >> +        FFALIGN(h->height_from_caller, 16) == FFALIGN(height, 16) &&
> >> +        h->width_from_caller  <= width &&
> >> +        h->height_from_caller <= height) {
> >> +        width  = h->width_from_caller;
> >> +        height = h->height_from_caller;
> >> +    } else {
> >> +        h->width_from_caller  = 0;
> >> +        h->height_from_caller = 0;
> >>      }
> > 
> > With this, seeking in a file could affect if croping is used
> > would something break if croping was unaffected by what was priorly
> > decoded ?
> 
> I don't know. Do you have a test case where this could break that i can
> check?

no, it was just an thought that came to my mind when looking at the
code. I dont remember seeing this break anything, it changed some
files output though unless these were caused by another patch i had
locally


[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Opposition brings concord. Out of discord comes the fairest harmony.
-- Heraclitus
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