From c85508f5a91cc0caf18ba33c941536bf8b99b81b Mon Sep 17 00:00:00 2001 From: Andreas Rheinhardt Date: Sun, 28 Apr 2024 01:45:47 +0200 Subject: [PATCH] avcodec/mpeg12dec: Allocate dummy frames for non-I fields MPEG-2 allows to pair an intra field (as first field) together with a P-field. In this case a conformant bitstream has to satisfy certain restrictions in order to ensure that only the I field is used for prediction. See section 7.6.3.5 of the MPEG-2 specifications. We do not check these restrictions; normally we simply allocate dummy frames for reference in order to avoid checks lateron. This happens in ff_mpv_frame_start() and therefore does not happen for a second field. This is inconsistent. Fix this by allocating these dummy frames for the second field, too. This already fixes two bugs: 1. Undefined pointer arithmetic in prefetch_motion() in mpegvideo_motion.c where it is simply presumed that the reference frame exists. 2. Several MPEG-2 hardware accelerations rely on last_picture being allocated for P pictures and next picture for B pictures; e.g. VDPAU returns VDP_STATUS_INVALID_HANDLE when decoding an I-P fields pair because the forward_reference was set incorrectly. Signed-off-by: Andreas Rheinhardt --- libavcodec/mpeg12dec.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/libavcodec/mpeg12dec.c b/libavcodec/mpeg12dec.c index 9fd765f030..f6ec528bce 100644 --- a/libavcodec/mpeg12dec.c +++ b/libavcodec/mpeg12dec.c @@ -1372,6 +1372,9 @@ static int mpeg_field_start(MpegEncContext *s, const uint8_t *buf, int buf_size) return ret; } } + ret = ff_mpv_alloc_dummy_frames(s); + if (ret < 0) + return ret; for (int i = 0; i < 3; i++) { s->current_picture.f->data[i] = s->current_picture_ptr->f->data[i]; @@ -1727,7 +1730,7 @@ static int slice_decode_thread(AVCodecContext *c, void *arg) * Handle slice ends. * @return 1 if it seems to be the last slice */ -static int slice_end(AVCodecContext *avctx, AVFrame *pict) +static int slice_end(AVCodecContext *avctx, AVFrame *pict, int *got_output) { Mpeg1Context *s1 = avctx->priv_data; MpegEncContext *s = &s1->mpeg_enc_ctx; @@ -1758,14 +1761,16 @@ static int slice_end(AVCodecContext *avctx, AVFrame *pict) return ret; ff_print_debug_info(s, s->current_picture_ptr, pict); ff_mpv_export_qp_table(s, pict, s->current_picture_ptr, FF_MPV_QSCALE_TYPE_MPEG2); + *got_output = 1; } else { /* latency of 1 frame for I- and P-frames */ - if (s->last_picture_ptr) { + if (s->last_picture_ptr && !s->last_picture_ptr->dummy) { int ret = av_frame_ref(pict, s->last_picture_ptr->f); if (ret < 0) return ret; ff_print_debug_info(s, s->last_picture_ptr, pict); ff_mpv_export_qp_table(s, pict, s->last_picture_ptr, FF_MPV_QSCALE_TYPE_MPEG2); + *got_output = 1; } } @@ -2204,14 +2209,9 @@ static int decode_chunks(AVCodecContext *avctx, AVFrame *picture, s2->er.error_count += s2->thread_context[i]->er.error_count; } - ret = slice_end(avctx, picture); + ret = slice_end(avctx, picture, got_output); if (ret < 0) return ret; - else if (ret) { - // FIXME: merge with the stuff in mpeg_decode_slice - if (s2->last_picture_ptr || s2->low_delay || s2->pict_type == AV_PICTURE_TYPE_B) - *got_output = 1; - } } s2->pict_type = 0;