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lavc/pngdec: always create a copy for APNG_DISPOSE_OP_BACKGROUND

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Calling av_frame_make_writable() from decoders is tricky, especially
when frame threading is used. It is much simpler and safer to just make
a private copy of the frame.
This is not expected to have a major performance impact, since
APNG_DISPOSE_OP_BACKGROUND is not used often and
av_frame_make_writable() would typically make a copy anyway.

Found-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Anton Khirnov 2021-04-08 10:46:54 +02:00 committed by Michael Niedermayer
parent caaf463311
commit b593abda6c
1 changed files with 11 additions and 7 deletions
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18
libavcodec/pngdec.c
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@ -89,6 +89,8 @@ typedef struct PNGDecContext {
int has_trns;
uint8_t transparent_color_be[6];
uint8_t *background_buf;
unsigned background_buf_allocated;
uint32_t palette[256];
uint8_t *crow_buf;
uint8_t *last_row;
@ -1079,19 +1081,20 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
ff_thread_await_progress(&s->last_picture, INT_MAX, 0);
// need to reset a rectangle to background:
// create a new writable copy
if (s->last_dispose_op == APNG_DISPOSE_OP_BACKGROUND) {
int ret = av_frame_make_writable(s->last_picture.f);
if (ret < 0)
return ret;
av_fast_malloc(&s->background_buf, &s->background_buf_allocated,
src_stride * p->height);
if (!s->background_buf)
return AVERROR(ENOMEM);
src = s->last_picture.f->data[0];
src_stride = s->last_picture.f->linesize[0];
memcpy(s->background_buf, src, src_stride * p->height);
for (y = s->last_y_offset; y < s->last_y_offset + s->last_h; y++) {
memset(s->last_picture.f->data[0] + src_stride * y +
memset(s->background_buf + src_stride * y +
s->bpp * s->last_x_offset, 0, s->bpp * s->last_w);
}
src = s->background_buf;
}
// copy unchanged rectangles from the last frame
@ -1716,6 +1719,7 @@ static av_cold int png_dec_end(AVCodecContext *avctx)
s->last_row_size = 0;
av_freep(&s->tmp_row);
s->tmp_row_size = 0;
av_freep(&s->background_buf);
av_freep(&s->iccp_data);
av_dict_free(&s->frame_metadata);