[FFmpeg-devel] [RFC] [PATCH 1/5] hwcontext: add a new AVHWFramesContext.opaque field

[Lynne <dev@lynne.ee>]

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This is a public field, settable before frames context initialization,
and propagated to any derived contexts.

API users can use it to store state and determine which context
is one of theirs.

This also allows decoders which create their own contexts to store
some state which would be freed only at context destruction.

Request for comments.

Patch attached.


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From a9bdbbb64acfcb0540727895b7be4027ab9955f9 Mon Sep 17 00:00:00 2001
From: Lynne <dev@lynne.ee>
Date: Tue, 13 Jun 2023 06:10:50 +0200
Subject: [PATCH 1/5] hwcontext: add a new AVHWFramesContext.opaque field

This is a public field, settable before frames context initialization,
and propagated to any derived contexts.

API users can use it to store state and determine which context
is one of theirs.

This also allows decoders which create their own contexts to store
some state which would be freed only at context destruction.
---
 libavutil/hwcontext.c | 6 ++++++
 libavutil/hwcontext.h | 9 +++++++++
 2 files changed, 15 insertions(+)

diff --git a/libavutil/hwcontext.c b/libavutil/hwcontext.c
index 3396598269..92a8cc907a 100644
--- a/libavutil/hwcontext.c
+++ b/libavutil/hwcontext.c
@@ -238,6 +238,7 @@ static void hwframe_ctx_free(void *opaque, uint8_t *data)
     av_buffer_unref(&ctx->internal->source_frames);
 
     av_buffer_unref(&ctx->device_ref);
+    av_buffer_unref(&ctx->opaque);
 
     av_freep(&ctx->hwctx);
     av_freep(&ctx->internal->priv);
@@ -913,6 +914,11 @@ int av_hwframe_ctx_create_derived(AVBufferRef **derived_frame_ctx,
     dst->sw_format = src->sw_format;
     dst->width     = src->width;
     dst->height    = src->height;
+    dst->opaque    = av_buffer_ref(src->opaque);
+    if (!dst->internal->source_frames) {
+        ret = AVERROR(ENOMEM);
+        goto fail;
+    }
 
     dst->internal->source_frames = av_buffer_ref(source_frame_ctx);
     if (!dst->internal->source_frames) {
diff --git a/libavutil/hwcontext.h b/libavutil/hwcontext.h
index 7ff08c8608..7655bee33f 100644
--- a/libavutil/hwcontext.h
+++ b/libavutil/hwcontext.h
@@ -227,6 +227,15 @@ typedef struct AVHWFramesContext {
      * Must be set by the user before calling av_hwframe_ctx_init().
      */
     int width, height;
+
+    /**
+     * Opaque data. Can be set before calling av_hwframe_ctx_init().
+     * MUST NOT be set afterwards. Will be unref'd along with the
+     * main context at closure.
+     *
+     * Will be propagated to any derived contexts.
+     */
+    AVBufferRef *opaque;
 } AVHWFramesContext;
 
 /**
-- 
2.40.1


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