[FFmpeg-devel] [PATCH v2] hevcdec: skip slices with missing PPS instead of skipping the entire packet

[Hendrik Leppkes <h.leppkes@gmail.com>]

Aborting decoding of the entire packet on a missing PPS can result in
missing the actual PPS on streams with badly ordered NALs, where the
SPS/PPS/VPS are stitched to the back of the previous frame, instead of
the beginning of the next frame.

Instead, skip the undecodable slice, and let the decoder process further
NALs in the same packet.

If this happens on the first slice, the entire frame will be discarded
later, otherwise on other slices the decode error flag will be set to
indicate a missing/corrupt slice.
---
 libavcodec/hevcdec.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libavcodec/hevcdec.c b/libavcodec/hevcdec.c
index 3aa70e2245..89381db240 100644
--- a/libavcodec/hevcdec.c
+++ b/libavcodec/hevcdec.c
@@ -575,7 +575,9 @@ static int hls_slice_header(HEVCContext *s)
     sh->pps_id = get_ue_golomb_long(gb);
     if (sh->pps_id >= HEVC_MAX_PPS_COUNT || !s->ps.pps_list[sh->pps_id]) {
         av_log(s->avctx, AV_LOG_ERROR, "PPS id out of range: %d\n", sh->pps_id);
-        return AVERROR_INVALIDDATA;
+        if (s->ref)
+            s->ref->frame->decode_error_flags |= FF_DECODE_ERROR_DECODE_SLICES;
+        return 1; // skip slice with missing PPS, allowing other NALs to be decoded
     }
     if (!sh->first_slice_in_pic_flag &&
         s->ps.pps != (HEVCPPS*)s->ps.pps_list[sh->pps_id]->data) {
-- 
2.33.0.windows.2

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