swscale/utils: add SwsFormat abstraction and helpers

Groups together all relevant color metadata from an AVFrame. While we could
use AVFrame directly, keeping it a separate struct has three advantages:

1. Functions accepting an SwsFormat will definitely not care about the
   data pointers.
2. It clearly separates sanitized and raw metadata, since the function to
   construct an SwsFormat from an AVFrame will also sanitize.
3. It's slightly more lightweight to pass around.

Move these into a new header file "utils.h" to avoid crowding
swscale_internal.h even more, and also to solve a circular dependency issue
down the line.

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Niklas Haas <git@haasn.dev>

1 files changed, 64 insertions, 0 deletions

diff --git a/libswscale/utils.c b/libswscale/utils.c
index 0c9e8d58fc..4419e3e627 100644
--- a/libswscale/utils.c
+++ b/libswscale/utils.c
@@ -1,4 +1,5 @@
 /*
+ * Copyright (C) 2024 Niklas Haas
  * Copyright (C) 2001-2003 Michael Niedermayer <michaelni@gmx.at>
  *
  * This file is part of FFmpeg.
@@ -59,6 +60,7 @@
 #include "rgb2rgb.h"
 #include "swscale.h"
 #include "swscale_internal.h"
+#include "utils.h"
 
 typedef struct FormatEntry {
     uint8_t is_supported_in         :1;
@@ -2645,3 +2647,65 @@ int ff_range_add(RangeList *rl, unsigned int start, unsigned int len)
 
     return 0;
 }
+
+/**
+ * This function also sanitizes and strips the input data, removing irrelevant
+ * fields for certain formats.
+ */
+SwsFormat ff_fmt_from_frame(const AVFrame *frame, int field)
+{
+    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(frame->format);
+    SwsFormat fmt = {
+        .width  = frame->width,
+        .height = frame->height,
+        .format = frame->format,
+        .range  = frame->color_range,
+        .prim   = frame->color_primaries,
+        .trc    = frame->color_trc,
+        .csp    = frame->colorspace,
+        .loc    = frame->chroma_location,
+        .desc   = desc,
+    };
+
+    av_assert1(fmt.width > 0);
+    av_assert1(fmt.height > 0);
+    av_assert1(fmt.format != AV_PIX_FMT_NONE);
+    av_assert0(desc);
+    if (desc->flags & (AV_PIX_FMT_FLAG_RGB | AV_PIX_FMT_FLAG_PAL | AV_PIX_FMT_FLAG_BAYER)) {
+        /* RGB-like family */
+        fmt.csp   = AVCOL_SPC_RGB;
+        fmt.range = AVCOL_RANGE_JPEG;
+    } else if (desc->flags & AV_PIX_FMT_FLAG_XYZ) {
+        fmt.csp   = AVCOL_SPC_UNSPECIFIED;
+        fmt.prim  = AVCOL_PRI_SMPTE428;
+        fmt.trc   = AVCOL_TRC_SMPTE428;
+    } else if (desc->nb_components < 3) {
+        /* Grayscale formats */
+        fmt.prim  = AVCOL_PRI_UNSPECIFIED;
+        fmt.csp   = AVCOL_SPC_UNSPECIFIED;
+        if (desc->flags & AV_PIX_FMT_FLAG_FLOAT)
+            fmt.range = AVCOL_RANGE_UNSPECIFIED;
+        else
+            fmt.range = AVCOL_RANGE_JPEG; // FIXME: this restriction should be lifted
+    }
+
+    switch (frame->format) {
+    case AV_PIX_FMT_YUVJ420P:
+    case AV_PIX_FMT_YUVJ411P:
+    case AV_PIX_FMT_YUVJ422P:
+    case AV_PIX_FMT_YUVJ444P:
+    case AV_PIX_FMT_YUVJ440P:
+        fmt.range = AVCOL_RANGE_JPEG;
+        break;
+    }
+
+    if (!desc->log2_chroma_w && !desc->log2_chroma_h)
+        fmt.loc = AVCHROMA_LOC_UNSPECIFIED;
+
+    if (frame->flags & AV_FRAME_FLAG_INTERLACED) {
+        fmt.height = (fmt.height + (field == FIELD_TOP)) >> 1;
+        fmt.interlaced = 1;
+    }
+
+    return fmt;
+}