Re: review

From a7449f432d1cdeadf7a85e7ebb8d2850f65ad68d Mon Sep 17 00:00:00 2001
From: Pradeep Kumar <[email protected]>
Date: Thu, 30 Jul 2026 14:39:34 +0530
Subject: [PATCH] avcodec/qsvdec: use MFXVideoDECODE_Reset on flush for fast
 keyframe decode path

The existing flush implementation always performs a full teardown and
reinitialization of the MFX session, which takes ~40-100 ms per call.
This is a critical regression for applications that decode only keyframes
and must flush the decoder between every frame (e.g. video management
software seeking and displaying I-frames).

Replace the unconditional reinit in qsv_decode_flush() with an in-place
MFXVideoDECODE_Reset() call when a live session exists.  Reset is
sufficient to clear the decoder state and is ~20x faster than a full
teardown+reinit cycle on ADL/RPL/PTL integrated graphics.

New flush logic:
- Call qsv_clear_async() only on the fast-reset path, immediately
  before MFXVideoDECODE_Reset().  This is the only place it is needed:
  Intel MediaSDK/VPL requires all outstanding async operations to be
  drained before Reset is called.
- On the full-reinit fallback (no session, or Reset fails), call
  qsv_decode_close_qsvcontext() which already drains the async fifo,
  frees the work-frame list and uninits pool/session.  A separate
  qsv_clear_async() call there was therefore redundant.
- After a full teardown, explicitly null q->session so the reinit
  guard in qsv_process_data() (if !q->session) correctly triggers
  instead of dereferencing the freed handle.

Signed-off-by: Pradeep <[email protected]>
---
 libavcodec/qsvdec.c | 73 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 72 insertions(+), 1 deletion(-)

diff --git a/libavcodec/qsvdec.c b/libavcodec/qsvdec.c
index a85c1785cf..58457dd23a 100644
--- a/libavcodec/qsvdec.c
+++ b/libavcodec/qsvdec.c
@@ -572,6 +572,33 @@ static void qsv_clear_unused_frames(QSVContext *q)
     }
 }
 
+static void qsv_clear_async(QSVContext *q)
+{
+    QSVAsyncFrame aframe;
+    QSVFrame *cur;
+
+    if (q->async_fifo) {
+        while (av_fifo_read(q->async_fifo, &aframe, 1) >= 0) {
+            if (aframe.frame && aframe.frame->queued > 0)
+                aframe.frame->queued -= 1;
+            av_freep(&aframe.sync);
+        }
+    }
+
+    cur = q->work_frames;
+    while (cur) {
+        cur->queued = 0;
+        if (cur->used && !cur->surface.Data.Locked) {
+            cur->used = 0;
+            av_frame_unref(cur->frame);
+        }
+        cur = cur->next;
+    }
+
+    q->zero_consume_run = 0;
+    q->reinit_flag = 0;
+}
+
 static int get_surface(AVCodecContext *avctx, QSVContext *q, mfxFrameSurface1 **surf)
 {
     QSVFrame *frame, **last;
@@ -1207,11 +1234,55 @@ static int qsv_decode_frame(AVCodecContext *avctx, AVFrame *frame,
 static void qsv_decode_flush(AVCodecContext *avctx)
 {
     QSVDecContext *s = avctx->priv_data;
+    mfxStatus sts;
+    mfxVideoParam param = { { { 0 } } };
 
     qsv_clear_buffers(s);
 
+    // Fast path: reset the decoder in-place without tearing down the session.
+    // qsv_clear_async() is only needed here because MFXVideoDECODE_Reset
+    // requires all outstanding async operations to be drained first.
+    // On the full-reinit path below, qsv_decode_close_qsvcontext() already
+    // handles async/frame/pool cleanup, so calling qsv_clear_async() there
+    // would be redundant.
+    if (s->qsv.session && s->qsv.initialized) {
+        qsv_clear_async(&s->qsv);
+
+        sts = MFXVideoDECODE_GetVideoParam(s->qsv.session, &param);
+        if (sts < 0) {
+            av_log(avctx, AV_LOG_WARNING,
+                   "MFXVideoDECODE_GetVideoParam failed (%d), forcing full reinit\n", sts);
+            goto full_reinit;
+        }
+
+        param.AsyncDepth  = s->qsv.async_depth;
+        param.IOPattern   = s->qsv.iopattern;
+        param.ExtParam    = s->qsv.ext_buffers;
+        param.NumExtParam = s->qsv.nb_ext_buffers;
+
+        sts = MFXVideoDECODE_Reset(s->qsv.session, &param);
+        if (sts < 0) {
+            av_log(avctx, AV_LOG_WARNING,
+                   "MFXVideoDECODE_Reset failed (%d), forcing full reinit\n", sts);
+            goto full_reinit;
+        }
+
+        s->qsv.frame_info = param.mfx.FrameInfo;
+        return;
+    }
+
+full_reinit:
+    // Full teardown: session missing, not yet initialized, or reset failed.
+    // qsv_decode_close_qsvcontext() clears async frames, the work-frame list,
+    // pool and session state, so no separate qsv_clear_async() is needed.
+    qsv_decode_close_qsvcontext(&s->qsv);
+    // qsv_decode_close_qsvcontext() does not null q->session (it doesn't need
+    // to on codec close). Since the QSVContext lives on across flush(), clear
+    // the dangling handle so the reinit path in qsv_process_data() takes the
+    // "no session" branch instead of dereferencing freed memory.
+    s->qsv.session      = NULL;
     s->qsv.orig_pix_fmt = AV_PIX_FMT_NONE;
-    s->qsv.initialized = 0;
+    s->qsv.initialized  = 0;
 }
 
 #define OFFSET(x) offsetof(QSVDecContext, x)
-- 
2.53.0.windows.1