Experimental reduced HEIF header

Add AVIF_ENABLE_EXPERIMENTAL_AVIR flag.
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

@@ -97,6 +97,7 @@ jobs:
         -DAVIF_BUILD_EXAMPLES=ON -DAVIF_BUILD_APPS=ON
         -DAVIF_BUILD_TESTS=ON -DAVIF_ENABLE_GTEST=ON -DAVIF_LOCAL_GTEST=ON
         -DAVIF_ENABLE_EXPERIMENTAL_YCGCO_R=ON
+        -DAVIF_ENABLE_EXPERIMENTAL_AVIR=ON
     - name: Build libavif (ninja)
       working-directory: ./build
       run: ninja

.github/workflows/ci-windows.yml

@@ -111,6 +111,7 @@ jobs:
         -DAVIF_BUILD_EXAMPLES=ON -DAVIF_BUILD_APPS=ON
         -DAVIF_BUILD_TESTS=ON -DAVIF_ENABLE_GTEST=ON -DAVIF_LOCAL_GTEST=ON
         -DAVIF_ENABLE_EXPERIMENTAL_YCGCO_R=ON
+        -DAVIF_ENABLE_EXPERIMENTAL_AVIR=ON
     - name: Build libavif (ninja)
       working-directory: ./build
       run: ninja

CMakeLists.txt

@@ -34,6 +34,7 @@ option(BUILD_SHARED_LIBS "Build shared avif library" ON)
 option(AVIF_ENABLE_WERROR "Treat all compiler warnings as errors" ON)
 
 option(AVIF_ENABLE_EXPERIMENTAL_YCGCO_R "Enable experimental YCgCo-R matrix code" 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)
@@ -262,6 +263,10 @@ if(AVIF_ENABLE_EXPERIMENTAL_YCGCO_R)
     add_compile_definitions(AVIF_ENABLE_EXPERIMENTAL_YCGCO_R)
 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                            : Minimize 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;
+    avifEncoderHeaderStrategy headerStrategy;
 
     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->headerStrategy = settings->headerStrategy;
     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.headerStrategy = AVIF_ENCODER_FULL_HEADER;
     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.headerStrategy = AVIF_ENCODER_MINIMIZE_HEADER;
+#endif // AVIF_ENABLE_EXPERIMENTAL_AVIR
         } else if (!strcmp(arg, "-d") || !strcmp(arg, "--depth")) {
             NEXTARG();
             input.requestedDepth = atoi(arg);

include/avif/avif.h

@@ -176,6 +176,20 @@ typedef enum avifResult
 
 AVIF_API const char * avifResultToString(avifResult result);
 
+// ---------------------------------------------------------------------------
+// avifEncoderHeaderStrategy
+
+typedef enum avifEncoderHeaderStrategy
+{
+    // Encodes as "avif" brand with a MetaBox and all its required boxes for maximum compatibility.
+    AVIF_ENCODER_FULL_HEADER,
+#if defined(AVIF_ENABLE_EXPERIMENTAL_AVIR)
+    // Encodes as "avir" brand with a CondensedImageBox to reduce the encoded file size.
+    // WARNING: Experimental feature. Produces files that are incompatible with older decoders.
+    AVIF_ENCODER_MINIMIZE_HEADER,
+#endif
+} avifEncoderHeaderStrategy;
+
 // ---------------------------------------------------------------------------
 // avifROData/avifRWData: Generic raw memory storage
 
@@ -1138,6 +1152,9 @@ typedef struct avifScalingMode
 //   call to avifEncoderAddImage().
 typedef struct avifEncoder
 {
+    // Defaults to AVIF_ENCODER_FULL_HEADER
+    avifEncoderHeaderStrategy headerStrategy;
+
     // Defaults to AVIF_CODEC_CHOICE_AUTO: Preference determined by order in availableCodecs table (avif.c)
     avifCodecChoice codecChoice;
 

include/avif/internal.h

@@ -453,6 +453,14 @@ typedef struct avifROStream
     // Index of the next byte in the raw stream.
     size_t offset;
 
+#if defined(AVIF_ENABLE_EXPERIMENTAL_AVIR)
+    // Index of the currently selected partial byte. Must be lower than offset.
+    // Only meaningful if numUsedBitsInPartialByte is not zero.
+    size_t offsetOfPartialByte;
+    // Number of bits already used in the currently selected partial byte.
+    size_t numUsedBitsInPartialByte;
+#endif
+
     // Error information, if any.
     avifDiagnostics * diag;
     const char * diagContext;
@@ -473,6 +481,10 @@ avifBool avifROStreamReadU32(avifROStream * stream, uint32_t * v);
 avifBool avifROStreamReadU32Endianness(avifROStream * stream, uint32_t * v, avifBool littleEndian);
 avifBool avifROStreamReadUX8(avifROStream * stream, uint64_t * v, uint64_t factor); // Reads a factor*8 sized uint, saves in v
 avifBool avifROStreamReadU64(avifROStream * stream, uint64_t * v);
+#if defined(AVIF_ENABLE_EXPERIMENTAL_AVIR)
+avifBool avifROStreamReadBits(avifROStream * stream, uint32_t * v, size_t bitCount);
+avifBool avifROStreamReadVarInt(avifROStream * stream, uint32_t * v);
+#endif
 avifBool avifROStreamReadString(avifROStream * stream, char * output, size_t outputSize);
 avifBool avifROStreamReadBoxHeader(avifROStream * stream, avifBoxHeader * header); // This fails if the size reported by the header cannot fit in the stream
 avifBool avifROStreamReadBoxHeaderPartial(avifROStream * stream, avifBoxHeader * header); // This doesn't require that the full box can fit in the stream
@@ -485,6 +497,14 @@ typedef struct avifRWStream
 
     // Index of the next byte in the raw stream.
     size_t offset;
+
+#if defined(AVIF_ENABLE_EXPERIMENTAL_AVIR)
+    // Index of the currently selected partial byte. Must be lower than offset.
+    // Only meaningful if numUsedBitsInPartialByte is not zero.
+    size_t offsetOfPartialByte;
+    // Number of bits already used in the currently selected partial byte.
+    size_t numUsedBitsInPartialByte;
+#endif
 } avifRWStream;
 
 uint8_t * avifRWStreamCurrent(avifRWStream * stream);
@@ -503,6 +523,10 @@ void avifRWStreamWriteU16(avifRWStream * stream, uint16_t v);
 void avifRWStreamWriteU32(avifRWStream * stream, uint32_t v);
 void avifRWStreamWriteU64(avifRWStream * stream, uint64_t v);
 void avifRWStreamWriteZeros(avifRWStream * stream, size_t byteCount);
+#if defined(AVIF_ENABLE_EXPERIMENTAL_AVIR)
+void avifRWStreamWriteBits(avifRWStream * stream, uint32_t v, size_t bitCount);
+void avifRWStreamWriteVarInt(avifRWStream * stream, uint32_t v);
+#endif // AVIF_ENABLE_EXPERIMENTAL_AVIR
 
 // This is to make it clear that the box size is currently unknown, and will be determined later (with a call to avifRWStreamFinishBox)
 #define AVIF_BOX_SIZE_TBD 0