[FFmpeg-cvslog] [ffmpeg] avcodec/libopenh264dec: implement flush callback (branch master)

[Scott Kidder via ffmpeg-cvslog]

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Git pushed a commit to branch master
in repository ffmpeg.

The following commit(s) were added to refs/heads/master by this push:
     new 883e8a6336 avcodec/libopenh264dec: implement flush callback
883e8a6336 is described below

commit 883e8a6336b2651f7be79a6a9aa5f3cc22937948
Author:     Scott Kidder <sc...@kidder.io>
AuthorDate: Wed May 20 17:17:24 2026 -0700
Commit:     Timo Rothenpieler <t...@rothenpieler.org>
CommitDate: Mon Aug 3 11:08:57 2026 +0000

    avcodec/libopenh264dec: implement flush callback
    
    Cisco's ISVCDecoder retains DPB and reference state across
    avcodec_flush_buffers(), causing the next IDR to be accepted but
    subsequent P-frames to fail decode after a seek or loop. Cisco's
    API does not expose a non-destructive reset; tear down and rebuild
    the decoder via the existing close/init callbacks.
    
    The .flush callback is void and cannot report a re-init failure, so
    svc_decode_frame() guards against a NULL decoder left behind by a
    failed re-init. svc_decode_init() now also tears the decoder back
    down on an Initialize() failure so that path leaves the same clean
    NULL state the guard expects and does not leak the ISVCDecoder.
    
    Signed-off-by: Scott Kidder <sc...@kidder.io>
---
 libavcodec/libopenh264dec.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/libavcodec/libopenh264dec.c b/libavcodec/libopenh264dec.c
index b6a9bba2dc..c9b2459653 100644
--- a/libavcodec/libopenh264dec.c
+++ b/libavcodec/libopenh264dec.c
@@ -42,12 +42,22 @@ static av_cold int svc_decode_close(AVCodecContext *avctx)
 {
     SVCContext *s = avctx->priv_data;
 
-    if (s->decoder)
+    if (s->decoder) {
         WelsDestroyDecoder(s->decoder);
+        s->decoder = NULL;
+    }
 
     return 0;
 }
 
+static av_cold int svc_decode_init(AVCodecContext *avctx);
+
+static void svc_decode_flush(AVCodecContext *avctx)
+{
+    svc_decode_close(avctx);
+    svc_decode_init(avctx);
+}
+
 static av_cold int svc_decode_init(AVCodecContext *avctx)
 {
     SVCContext *s = avctx->priv_data;
@@ -75,6 +85,7 @@ static av_cold int svc_decode_init(AVCodecContext *avctx)
 
     if ((*s->decoder)->Initialize(s->decoder, &param) != cmResultSuccess) {
         av_log(avctx, AV_LOG_ERROR, "Initialize failed\n");
+        svc_decode_close(avctx);
         return AVERROR_UNKNOWN;
     }
 
@@ -95,6 +106,15 @@ static int svc_decode_frame(AVCodecContext *avctx, AVFrame 
*avframe,
     int opt;
 #endif
 
+    /* svc_decode_flush() tears the decoder down and re-initializes it. If that
+     * re-init failed (e.g. WelsCreateDecoder/Initialize OOM) s->decoder is 
left
+     * NULL; the void flush callback cannot report this, so guard here to turn 
a
+     * NULL dereference into a recoverable error. */
+    if (!s->decoder) {
+        av_log(avctx, AV_LOG_ERROR, "decoder not initialized\n");
+        return AVERROR(EINVAL);
+    }
+
     if (!avpkt->data) {
 #if OPENH264_VER_AT_LEAST(1, 9)
         int end_of_stream = 1;
@@ -162,6 +182,7 @@ const FFCodec ff_libopenh264_decoder = {
     .init           = svc_decode_init,
     FF_CODEC_DECODE_CB(svc_decode_frame),
     .close          = svc_decode_close,
+    .flush          = svc_decode_flush,
     .p.capabilities = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_DR1,
     .caps_internal  = FF_CODEC_CAP_SETS_PKT_DTS |
                       FF_CODEC_CAP_INIT_CLEANUP,

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