Experimental reduced HEIF header

Add AVIF_ENABLE_EXPERIMENTAL_AVIR flag.
Add avifHeaderFormat headerFormat member to avifEncoder.
Remove a few hundred bytes of container boilerplate for simple images.
This prototype uses a small box that expands in meaning to a full meta
box with all defined items and properties.

Warning: This feature is experimental and forbidden by the current
AVIF specification.

.github/workflows/ci-unix-static.yml

@@ -98,6 +98,7 @@ jobs:
         -DAVIF_BUILD_TESTS=ON -DAVIF_ENABLE_GTEST=ON -DAVIF_LOCAL_GTEST=ON
         -DAVIF_ENABLE_EXPERIMENTAL_YCGCO_R=ON
         -DAVIF_ENABLE_EXPERIMENTAL_GAIN_MAP=ON
+        -DAVIF_ENABLE_EXPERIMENTAL_AVIR=ON
     - name: Build libavif (ninja)
       working-directory: ./build
       run: ninja

.github/workflows/ci-windows.yml

@@ -112,6 +112,7 @@ jobs:
         -DAVIF_BUILD_TESTS=ON -DAVIF_ENABLE_GTEST=ON -DAVIF_LOCAL_GTEST=ON
         -DAVIF_ENABLE_EXPERIMENTAL_YCGCO_R=ON
         -DAVIF_ENABLE_EXPERIMENTAL_GAIN_MAP=ON
+        -DAVIF_ENABLE_EXPERIMENTAL_AVIR=ON
     - name: Build libavif (ninja)
       working-directory: ./build
       run: ninja

CHANGELOG.md

@@ -17,6 +17,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   in the future. Files created now might not decode in a future version.
   This feature is off by default and must be enabled with the
   AVIF_ENABLE_EXPERIMENTAL_GAIN_MAP compilation flag.
+* Add the headerFormat member of new type avifHeaderFormat to avifEncoder.
+* Add experimental API for reading and writing "avir"-branded AVIF files
+  behind the compilation flag AVIF_ENABLE_EXPERIMENTAL_AVIR.
 
 ### Changed
 * Update svt.cmd/svt.sh: v1.7.0

CMakeLists.txt

@@ -37,6 +37,7 @@ option(AVIF_ENABLE_EXPERIMENTAL_YCGCO_R "Enable experimental YCgCo-R matrix code
 option(AVIF_ENABLE_EXPERIMENTAL_GAIN_MAP
        "Enable experimental gain map code (for HDR images that look good both on HDR and SDR displays)" OFF
 )
+option(AVIF_ENABLE_EXPERIMENTAL_AVIR "Enable experimental reduced header" OFF)
 
 option(AVIF_CODEC_AOM "Use the AOM codec for encoding/decoding (see AVIF_CODEC_AOM_DECODE/AVIF_CODEC_AOM_ENCODE)" OFF)
 option(AVIF_CODEC_DAV1D "Use the dav1d codec for decoding" OFF)
@@ -269,6 +270,10 @@ if(AVIF_ENABLE_EXPERIMENTAL_GAIN_MAP)
     add_compile_definitions(AVIF_ENABLE_EXPERIMENTAL_GAIN_MAP)
 endif()
 
+if(AVIF_ENABLE_EXPERIMENTAL_AVIR)
+    add_compile_definitions(AVIF_ENABLE_EXPERIMENTAL_AVIR)
+endif()
+
 set(AVIF_SRCS
     src/alpha.c
     src/avif.c

apps/avifenc.c

@@ -97,6 +97,9 @@ static void syntaxLong(void)
     printf("    -j,--jobs J                       : Number of jobs (worker threads, default: 1. Use \"all\" to use all available cores)\n");
     printf("    --no-overwrite                    : Never overwrite existing output file\n");
     printf("    -o,--output FILENAME              : Instead of using the last filename given as output, use this filename\n");
+#if defined(AVIF_ENABLE_EXPERIMENTAL_AVIR)
+    printf("    --avir                            : Use reduced header if possible\n");
+#endif
     printf("    -l,--lossless                     : Set all defaults to encode losslessly, and emit warnings when settings/input don't allow for it\n");
     printf("    -d,--depth D                      : Output depth [8,10,12]. (JPEG/PNG only; For y4m or stdin, depth is retained)\n");
     printf("    -y,--yuv FORMAT                   : Output format [default=auto, 444, 422, 420, 400]. Ignored for y4m or stdin (y4m format is retained)\n");
@@ -669,6 +672,7 @@ typedef struct
     avifBool autoTiling;
     avifBool progressive;
     int speed;
+    avifHeaderFormat headerFormat;
 
     int paspCount;
     uint32_t paspValues[8]; // only the first two are used
@@ -888,6 +892,7 @@ static avifBool avifEncodeImagesFixedQuality(const avifSettings * settings,
     encoder->autoTiling = settings->autoTiling;
     encoder->codecChoice = settings->codecChoice;
     encoder->speed = settings->speed;
+    encoder->headerFormat = settings->headerFormat;
     encoder->timescale = settings->outputTiming.timescale;
     encoder->keyframeInterval = settings->keyframeInterval;
     encoder->repetitionCount = settings->repetitionCount;
@@ -1107,6 +1112,7 @@ int main(int argc, char * argv[])
     settings.autoTiling = AVIF_FALSE;
     settings.progressive = AVIF_FALSE;
     settings.speed = 6;
+    settings.headerFormat = AVIF_HEADER_FULL;
     settings.repetitionCount = AVIF_REPETITION_COUNT_INFINITE;
     settings.keyframeInterval = 0;
     settings.ignoreExif = AVIF_FALSE;
@@ -1177,6 +1183,10 @@ int main(int argc, char * argv[])
         } else if (!strcmp(arg, "-o") || !strcmp(arg, "--output")) {
             NEXTARG();
             outputFilename = arg;
+#if defined(AVIF_ENABLE_EXPERIMENTAL_AVIR)
+        } else if (!strcmp(arg, "--avir")) {
+            settings.headerFormat = AVIF_HEADER_REDUCED;
+#endif // AVIF_ENABLE_EXPERIMENTAL_AVIR
         } else if (!strcmp(arg, "-d") || !strcmp(arg, "--depth")) {
             NEXTARG();
             input.requestedDepth = atoi(arg);

include/avif/avif.h

@@ -184,6 +184,21 @@ typedef enum avifResult
 
 AVIF_API const char * avifResultToString(avifResult result);
 
+// ---------------------------------------------------------------------------
+// avifHeaderFormat
+
+typedef enum avifHeaderFormat
+{
+    // AVIF file with an "avif" brand, a MetaBox and all its required boxes for maximum compatibility.
+    AVIF_HEADER_FULL,
+#if defined(AVIF_ENABLE_EXPERIMENTAL_AVIR)
+    // AVIF file with an "avir" brand and a CondensedImageBox to reduce the encoded file size.
+    // This is based on the m64572 "Condensed image item" MPEG proposal for HEIF.
+    // WARNING: Experimental feature. Produces files that are incompatible with older decoders.
+    AVIF_HEADER_REDUCED,
+#endif
+} avifHeaderFormat;
+
 // ---------------------------------------------------------------------------
 // avifROData/avifRWData: Generic raw memory storage
 
@@ -1297,6 +1312,9 @@ typedef struct avifEncoder
 
     // Version 1.0.0 ends here. Add any new members after this line.
 
+    // Defaults to AVIF_HEADER_FULL
+    avifHeaderFormat headerFormat;
+
 #if defined(AVIF_ENABLE_EXPERIMENTAL_GAIN_MAP)
     int qualityGainMap; // changeable encoder setting
 #endif

include/avif/internal.h

@@ -238,6 +238,19 @@ typedef enum avifItemCategory
 #endif
 } avifItemCategory;
 
+// ---------------------------------------------------------------------------
+
+#if defined(AVIF_ENABLE_EXPERIMENTAL_AVIR)
+// AVIF color_type field meaning in CondensedImageBox
+typedef enum avifConiColorType
+{
+    AVIF_CONI_COLOR_TYPE_SRGB = 0,
+    AVIF_CONI_COLOR_TYPE_NCLX_5BIT = 1,
+    AVIF_CONI_COLOR_TYPE_NCLX_8BIT = 2,
+    AVIF_CONI_COLOR_TYPE_ICC = 3
+} avifConiColorType;
+#endif // AVIF_ENABLE_EXPERIMENTAL_AVIR
+
 // ---------------------------------------------------------------------------
 // Grid AVIF images