The decoder never marks pictures as I-frames, which results in no
keyframe indication and incorrect frame skipping, in cases when
keyframes should be decoded.
This commit works around this decoder limitation and marks I-frames
and keyframes based on "freeze picture release" bit in h261 picture
header. This reflects h261enc behavior.
---
libavcodec/h261.h | 1 +
libavcodec/h261dec.c | 27 ++++++++++++++++++---------
2 files changed, 19 insertions(+), 9 deletions(-)
diff --git a/libavcodec/h261.h b/libavcodec/h261.h
index 399a404b2b..6662d38d6d 100644
--- a/libavcodec/h261.h
+++ b/libavcodec/h261.h
@@ -37,6 +37,7 @@
typedef struct H261Context {
MpegEncContext s;
+ int freeze_picture_release; // 1 if freeze picture release bit is set in
the picture header
int current_mba;
int mba_diff;
int mtype;
diff --git a/libavcodec/h261dec.c b/libavcodec/h261dec.c
index 14a874c45d..3b1711a21d 100644
--- a/libavcodec/h261dec.c
+++ b/libavcodec/h261dec.c
@@ -502,9 +502,9 @@ static int h261_decode_picture_header(H261Context *h)
s->avctx->framerate = (AVRational) { 30000, 1001 };
/* PTYPE starts here */
- skip_bits1(&s->gb); /* split screen off */
- skip_bits1(&s->gb); /* camera off */
- skip_bits1(&s->gb); /* freeze picture release off */
+ skip_bits1(&s->gb); /* split screen indicator */
+ skip_bits1(&s->gb); /* document camera indicator */
+ h->freeze_picture_release = get_bits1(&s->gb); /* freeze picture release */
format = get_bits1(&s->gb);
@@ -532,7 +532,8 @@ static int h261_decode_picture_header(H261Context *h)
/* H.261 has no I-frames, but if we pass AV_PICTURE_TYPE_I for the first
* frame, the codec crashes if it does not contain all I-blocks
- * (e.g. when a packet is lost). */
+ * (e.g. when a packet is lost). We will fix the picture type in the
+ * output frame based on h->freeze_picture_release later. */
s->pict_type = AV_PICTURE_TYPE_P;
h->gob_number = 0;
@@ -590,6 +591,7 @@ static int h261_decode_frame(AVCodecContext *avctx, void
*data,
H261Context *h = avctx->priv_data;
MpegEncContext *s = &h->s;
int ret;
+ enum AVPictureType pict_type;
AVFrame *pict = data;
ff_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
@@ -630,15 +632,17 @@ retry:
goto retry;
}
- // for skipping the frame
- s->current_picture.f->pict_type = s->pict_type;
- s->current_picture.f->key_frame = s->pict_type == AV_PICTURE_TYPE_I;
+ // for skipping the frame and keyframe markup
+ pict_type = h->freeze_picture_release ? AV_PICTURE_TYPE_I : s->pict_type;
- if ((avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type ==
AV_PICTURE_TYPE_B) ||
- (avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type !=
AV_PICTURE_TYPE_I) ||
+ if ((avctx->skip_frame >= AVDISCARD_NONREF && pict_type ==
AV_PICTURE_TYPE_B) ||
+ (avctx->skip_frame >= AVDISCARD_NONKEY && pict_type !=
AV_PICTURE_TYPE_I) ||
avctx->skip_frame >= AVDISCARD_ALL)
return get_consumed_bytes(s, buf_size);
+ s->current_picture.f->pict_type = s->pict_type;
+ s->current_picture.f->key_frame = s->pict_type == AV_PICTURE_TYPE_I;
+
if (ff_mpv_frame_start(s, avctx) < 0)
return -1;
@@ -660,6 +664,11 @@ retry:
if ((ret = av_frame_ref(pict, s->current_picture_ptr->f)) < 0)
return ret;
+
+ // fix picture type and correctly mark keyframes
+ pict->pict_type = pict_type;
+ pict->key_frame = pict_type == AV_PICTURE_TYPE_I;
+
ff_print_debug_info(s, s->current_picture_ptr, pict);
*got_frame = 1;
--
2.20.1
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