[FFmpeg-devel] [PATCH 2/7] lavfi/buffersink: add a flag for retrieving stream parameters

[Anton Khirnov]

This way, av_buffersink_get_frame_flags() can replace almost all
av_buffersink_get_*(), including some future parameters we will want to
export.
---
 doc/APIchanges           |  1 +
 libavfilter/buffersink.c | 47 ++++++++++++++++++++++++++++++++++++++++
 libavfilter/buffersink.h | 16 ++++++++++++--
 3 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index b392c756d7..5ddd7189f8 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -4,6 +4,7 @@ API changes, most recent first:
 
 2024-09-xx - xxxxxxxxxx - lavfi 10.4.100
   Buffersink now sets AVFrame.time_base on the frames it outputs.
+  Add AV_BUFFERSINK_FLAG_PARAMS.
 
 2024-09-23 - xxxxxxxxxx - lavc 61.18.100 - avcodec.h
   Add a new flag AV_CODEC_EXPORT_DATA_ENHANCEMENTS for export_side_data.
diff --git a/libavfilter/buffersink.c b/libavfilter/buffersink.c
index 575075ff47..d9cd074f17 100644
--- a/libavfilter/buffersink.c
+++ b/libavfilter/buffersink.c
@@ -128,8 +128,55 @@ static int get_frame_internal(AVFilterContext *ctx, AVFrame *frame, int flags, i
     }
 }
 
+static int get_frame_params(AVFilterContext *ctx, AVFrame *frame)
+{
+    FilterLink *l = ff_filter_link(ctx->inputs[0]);
+    int ret = 0;
+
+    frame->time_base = l->pub.time_base;
+    frame->format    = l->pub.format;
+
+    switch (l->pub.type) {
+    case AVMEDIA_TYPE_AUDIO:
+        ret = av_channel_layout_copy(&frame->ch_layout, &l->pub.ch_layout);
+        if (ret < 0)
+            goto fail;
+
+        frame->sample_rate          = l->pub.sample_rate;
+        break;
+    case AVMEDIA_TYPE_VIDEO:
+        frame->width                = l->pub.w;
+        frame->height               = l->pub.h;
+        frame->sample_aspect_ratio  = l->pub.sample_aspect_ratio;
+        frame->colorspace           = l->pub.colorspace;
+        frame->color_range          = l->pub.color_range;
+        break;
+    default: av_assert0(0);
+    }
+
+    if (l->hw_frames_ctx) {
+        frame->hw_frames_ctx = av_buffer_ref(l->hw_frames_ctx);
+        if (!frame->hw_frames_ctx) {
+            ret = AVERROR(ENOMEM);
+            goto fail;
+        }
+    }
+
+    return 0;
+fail:
+    av_frame_unref(frame);
+    return ret;
+}
+
 int attribute_align_arg av_buffersink_get_frame_flags(AVFilterContext *ctx, AVFrame *frame, int flags)
 {
+    if (flags & AV_BUFFERSINK_FLAG_PARAMS) {
+        if (flags & ~AV_BUFFERSINK_FLAG_PARAMS)
+            return AVERROR(EINVAL);
+
+        return get_frame_params(ctx, frame);
+    }
+
     return get_frame_internal(ctx, frame, flags,
                               ff_filter_link(ctx->inputs[0])->min_samples);
 }
diff --git a/libavfilter/buffersink.h b/libavfilter/buffersink.h
index 361d603679..9c4468af5b 100644
--- a/libavfilter/buffersink.h
+++ b/libavfilter/buffersink.h
@@ -87,14 +87,26 @@ int av_buffersink_get_frame_flags(AVFilterContext *ctx, AVFrame *frame, int flag
  * reference, but not remove it from the buffer. This is useful if you
  * need only to read a video/samples buffer, without to fetch it.
  */
-#define AV_BUFFERSINK_FLAG_PEEK 1
+#define AV_BUFFERSINK_FLAG_PEEK         (1 << 0)
 
 /**
  * Tell av_buffersink_get_buffer_ref() not to request a frame from its input.
  * If a frame is already buffered, it is read (and removed from the buffer),
  * but if no frame is present, return AVERROR(EAGAIN).
  */
-#define AV_BUFFERSINK_FLAG_NO_REQUEST 2
+#define AV_BUFFERSINK_FLAG_NO_REQUEST   (1 << 1)
+
+/**
+ * Retrieve stream parameters rather than frame data.
+ *
+ * When this flag is set, av_buffersink_get_frame_flags() fills the non-data
+ * fields of the supplied frame without causing any filtergraph activity.
+ *
+ * @note While frame data will be NULL, certain other allocated fields may be
+ * filled (e.g. ch_layout, hw_frames_ctx), so the frame should still be
+ * unreffed before reuse.
+ */
+#define AV_BUFFERSINK_FLAG_PARAMS       (1 << 2)
 
 /**
  * Set the frame size for an audio buffer sink.
-- 
2.43.0