lavc/videotoolbox: do not pass AVCodecContext to decoder output callback

The opaque parameter for the callback is set in videotoolbox_start(),
called when the hwaccel is initialized. When frame threading is used,
avctx will be the context corresponding to the frame thread currently
doing the decoding. Using this same codec context in all subsequent
invocations of the decoder callback (even those triggered by a different
frame thread) is unsafe, and broken after
cc867f2c09d2b69cee8a0eccd62aff002cbbfe11, since each frame thread now
cleans up its hwaccel state after decoding each frame.

Fix this by passing hwaccel_priv_data as the opaque parameter, which
exists in a single instance forwarded between all frame threads.

The only other use of AVCodecContext in the decoder output callback is
as a logging context. For this purpose, store a logging context in
hwaccel_priv_data.

2 files changed, 8 insertions, 4 deletions

diff --git a/libavcodec/videotoolbox.c b/libavcodec/videotoolbox.c
index ce83c2594a..d61d310600 100644
--- a/libavcodec/videotoolbox.c
+++ b/libavcodec/videotoolbox.c
@@ -690,8 +690,7 @@ static void videotoolbox_decoder_callback(void *opaque,
                                           CMTime pts,
                                           CMTime duration)
 {
-    AVCodecContext *avctx = opaque;
-    VTContext *vtctx = avctx->internal->hwaccel_priv_data;
+    VTContext *vtctx = opaque;
 
     if (vtctx->frame) {
         CVPixelBufferRelease(vtctx->frame);
@@ -699,7 +698,8 @@ static void videotoolbox_decoder_callback(void *opaque,
     }
 
     if (!image_buffer) {
-        av_log(avctx, status ? AV_LOG_WARNING : AV_LOG_DEBUG, "vt decoder cb: output image buffer is null: %i\n", status);
+        av_log(vtctx->logctx, status ? AV_LOG_WARNING : AV_LOG_DEBUG,
+               "vt decoder cb: output image buffer is null: %i\n", status);
         return;
     }
 
@@ -949,7 +949,7 @@ static int videotoolbox_start(AVCodecContext *avctx)
                                                      videotoolbox->cv_pix_fmt_type);
 
     decoder_cb.decompressionOutputCallback = videotoolbox_decoder_callback;
-    decoder_cb.decompressionOutputRefCon   = avctx;
+    decoder_cb.decompressionOutputRefCon   = avctx->internal->hwaccel_priv_data;
 
     status = VTDecompressionSessionCreate(NULL,                      // allocator
                                           videotoolbox->cm_fmt_desc, // videoFormatDescription
@@ -1179,6 +1179,8 @@ int ff_videotoolbox_common_init(AVCodecContext *avctx)
     AVHWFramesContext *hw_frames;
     int err;
 
+    vtctx->logctx = avctx;
+
     // Old API - do nothing.
     if (avctx->hwaccel_context)
         return 0;
diff --git a/libavcodec/vt_internal.h b/libavcodec/vt_internal.h
index 54a11fd1b5..9502d7c7dc 100644
--- a/libavcodec/vt_internal.h
+++ b/libavcodec/vt_internal.h
@@ -45,6 +45,8 @@ typedef struct VTContext {
     // Current H264 parameters (used to trigger decoder restart on SPS changes).
     uint8_t                     sps[3];
     bool                        reconfig_needed;
+
+    void *logctx;
 } VTContext;
 
 int ff_videotoolbox_alloc_frame(AVCodecContext *avctx, AVFrame *frame);