[FFmpeg-devel] [PATCH] avcodec/hevc: reset long_term_rps.nb_refs for IDR (PR #20774)

[Zhao Zhili via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #20774 opened by Zhao Zhili (quink)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20774
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20774.patch

For mv-hevc, the second layer of IDR frame can be a P slice.
long_term_rps wasn't been reset before the patch, which leading to
ff_hevc_frame_nb_refs return incorrect result.

This fix decoding failure for samples from Pico VR.


>From 5adc48455a3750c2903989d173552ee4f65c21c6 Mon Sep 17 00:00:00 2001
From: Zhao Zhili <zhilizhao@tencent.com>
Date: Tue, 28 Oct 2025 20:20:23 +0800
Subject: [PATCH 1/2] avcodec/hevc: remove an always true condition

long_rps is &sh->long_term_rps.
---
 libavcodec/hevc/refs.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/libavcodec/hevc/refs.c b/libavcodec/hevc/refs.c
index 15f37bfcd8..ccf7258ec4 100644
--- a/libavcodec/hevc/refs.c
+++ b/libavcodec/hevc/refs.c
@@ -626,10 +626,8 @@ int ff_hevc_frame_nb_refs(const SliceHeader *sh, const HEVCPPS *pps,
             ret += !!(rps->used & (1 << i));
     }
 
-    if (long_rps) {
-        for (i = 0; i < long_rps->nb_refs; i++)
-            ret += !!long_rps->used[i];
-    }
+    for (i = 0; i < long_rps->nb_refs; i++)
+        ret += !!long_rps->used[i];
 
     if (sh->inter_layer_pred) {
         av_assert0(pps->sps->vps->num_direct_ref_layers[layer_idx] < 2);
-- 
2.49.1


>From 85420d061c7ad7928acab6f9c244726b0b7a5159 Mon Sep 17 00:00:00 2001
From: Zhao Zhili <zhilizhao@tencent.com>
Date: Tue, 28 Oct 2025 20:25:12 +0800
Subject: [PATCH 2/2] avcodec/hevc: reset long_term_rps.nb_refs for IDR

For mv-hevc, the second layer of IDR frame can be a P slice.
long_term_rps wasn't been reset before the patch, which leading to
ff_hevc_frame_nb_refs return incorrect result.

This fix decoding failure for samples from Pico VR.
---
 libavcodec/hevc/hevcdec.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/libavcodec/hevc/hevcdec.c b/libavcodec/hevc/hevcdec.c
index 8d432a9a1f..3f471dbc14 100644
--- a/libavcodec/hevc/hevcdec.c
+++ b/libavcodec/hevc/hevcdec.c
@@ -917,6 +917,7 @@ static int hls_slice_header(SliceHeader *sh, const HEVCContext *s, GetBitContext
             sh->short_term_ref_pic_set_size     = 0;
             sh->short_term_rps                  = NULL;
             sh->long_term_ref_pic_set_size      = 0;
+            sh->long_term_rps.nb_refs           = 0;
             sh->slice_temporal_mvp_enabled_flag = 0;
         }
 
-- 
2.49.1

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