[FFmpeg-devel] [PATCH 01/12] avutil/frame: add AVFrame.alpha_mode

* [FFmpeg-devel] [PATCH 01/12] avutil/frame: add AVFrame.alpha_mode
@ 2025-02-19 20:45 Niklas Haas
  2025-02-19 20:45 ` [FFmpeg-devel] [PATCH 02/12] fftools/ffprobe: add support for AVFrame.alpha_mode Niklas Haas
                   ` (12 more replies)
  0 siblings, 13 replies; 18+ messages in thread
From: Niklas Haas @ 2025-02-19 20:45 UTC (permalink / raw)
  To: ffmpeg-devel; +Cc: Niklas Haas

From: Niklas Haas <git@haasn.dev>

FFmpeg currently handles alpha in a quasi-arbitrary way. Some filters/codecs
assume alpha is premultiplied, others assume it is independent. If there is
to be any hope for order in this chaos, we need to start by defining an enum
for the possible range of values.
---
 doc/APIchanges      |  4 ++++
 libavutil/frame.c   |  2 ++
 libavutil/frame.h   |  7 +++++++
 libavutil/pixdesc.c | 27 +++++++++++++++++++++++++++
 libavutil/pixdesc.h | 10 ++++++++++
 libavutil/pixfmt.h  | 10 ++++++++++
 libavutil/version.h |  2 +-
 7 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index ac506f4b56..601013b018 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -2,6 +2,10 @@ The last version increases of all libraries were on 2024-03-07
 
 API changes, most recent first:
 
+2025-02-xx - xxxxxxxxxx - lavu 59.58.100 - frame.h pixfmt.h
+  Add AVAlphaMode, AVFrame.alpha_mode, av_alpha_mode_name() and
+  av_alpha_mode_from_name().
+
 2025-02-xx - xxxxxxxxxx - lavu 59.57.100 - log.h
   Add flags AV_LOG_PRINT_TIME and AV_LOG_PRINT_DATETIME.
 
diff --git a/libavutil/frame.c b/libavutil/frame.c
index 492b467ebd..cc906dbe21 100644
--- a/libavutil/frame.c
+++ b/libavutil/frame.c
@@ -84,6 +84,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
     frame->colorspace          = AVCOL_SPC_UNSPECIFIED;
     frame->color_range         = AVCOL_RANGE_UNSPECIFIED;
     frame->chroma_location     = AVCHROMA_LOC_UNSPECIFIED;
+    frame->alpha_mode          = AVALPHA_MODE_UNSPECIFIED;
     frame->flags               = 0;
 }
 
@@ -364,6 +365,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
     dst->colorspace             = src->colorspace;
     dst->color_range            = src->color_range;
     dst->chroma_location        = src->chroma_location;
+    dst->alpha_mode             = src->alpha_mode;
 
     av_dict_copy(&dst->metadata, src->metadata, 0);
 
diff --git a/libavutil/frame.h b/libavutil/frame.h
index 49260ae2dd..6e53135d27 100644
--- a/libavutil/frame.h
+++ b/libavutil/frame.h
@@ -822,6 +822,13 @@ typedef struct AVFrame {
      * Duration of the frame, in the same units as pts. 0 if unknown.
      */
     int64_t duration;
+
+    /**
+     * Indicates how the alpha channel of the video is to be handled.
+     * - encoding: Set by user
+     * - decoding: Set by libavcodec
+     */
+    enum AVAlphaMode alpha_mode;
 } AVFrame;
 
 
diff --git a/libavutil/pixdesc.c b/libavutil/pixdesc.c
index 6fe83cd16b..f4eb3d5074 100644
--- a/libavutil/pixdesc.c
+++ b/libavutil/pixdesc.c
@@ -3152,6 +3152,12 @@ static const char * const chroma_location_names[] = {
     [AVCHROMA_LOC_BOTTOM] = "bottom",
 };
 
+static const char * const alpha_mode_names[] = {
+    [AVALPHA_MODE_UNSPECIFIED] = "unspecified",
+    [AVALPHA_MODE_PREMULTIPLIED] = "premultiplied",
+    [AVALPHA_MODE_STRAIGHT] = "straight",
+};
+
 static enum AVPixelFormat get_pix_fmt_internal(const char *name)
 {
     enum AVPixelFormat pix_fmt;
@@ -3685,3 +3691,24 @@ enum AVChromaLocation av_chroma_location_pos_to_enum(int xpos, int ypos)
     }
     return AVCHROMA_LOC_UNSPECIFIED;
 }
+
+const char *av_alpha_mode_name(enum AVAlphaMode mode)
+{
+    return (unsigned) mode < AVALPHA_MODE_NB ?
+        alpha_mode_names[mode] : NULL;
+}
+
+enum AVAlphaMode av_alpha_mode_from_name(const char *name)
+{
+    int i;
+
+    for (i = 0; i < FF_ARRAY_ELEMS(alpha_mode_names); i++) {
+        if (!alpha_mode_names[i])
+            continue;
+
+        if (av_strstart(name, alpha_mode_names[i], NULL))
+            return i;
+    }
+
+    return AVERROR(EINVAL);
+}
diff --git a/libavutil/pixdesc.h b/libavutil/pixdesc.h
index ba2f632814..0cc70eb64c 100644
--- a/libavutil/pixdesc.h
+++ b/libavutil/pixdesc.h
@@ -291,6 +291,16 @@ int av_chroma_location_enum_to_pos(int *xpos, int *ypos, enum AVChromaLocation p
  */
 enum AVChromaLocation av_chroma_location_pos_to_enum(int xpos, int ypos);
 
+/**
+ * @return the name for provided alpha mode or NULL if unknown.
+ */
+const char *av_alpha_mode_name(enum AVAlphaMode mode);
+
+/**
+ * @return the AVAlphaMode value for name or an AVError if not found.
+ */
+enum AVAlphaMode av_alpha_mode_from_name(const char *name);
+
 /**
  * Return the pixel format corresponding to name.
  *
diff --git a/libavutil/pixfmt.h b/libavutil/pixfmt.h
index a64d40ad07..8af64a383d 100644
--- a/libavutil/pixfmt.h
+++ b/libavutil/pixfmt.h
@@ -760,4 +760,14 @@ enum AVChromaLocation {
     AVCHROMA_LOC_NB               ///< Not part of ABI
 };
 
+/**
+ * Correlation between the alpha channel and color values.
+ */
+enum AVAlphaMode {
+    AVALPHA_MODE_UNSPECIFIED   = 0, ///< Unknown alpha handling, or no alpha channel
+    AVALPHA_MODE_PREMULTIPLIED = 1, ///< Alpha channel is multiplied into color values
+    AVALPHA_MODE_STRAIGHT      = 2, ///< Alpha channel is independent of color values
+    AVALPHA_MODE_NB                 ///< Not part of ABI
+};
+
 #endif /* AVUTIL_PIXFMT_H */
diff --git a/libavutil/version.h b/libavutil/version.h
index ee4a36cb17..4b584fd569 100644
--- a/libavutil/version.h
+++ b/libavutil/version.h
@@ -79,7 +79,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  59
-#define LIBAVUTIL_VERSION_MINOR  57
+#define LIBAVUTIL_VERSION_MINOR  58
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
-- 
2.47.0

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