dirac: add Comments and references to the standard

Signed-off-by: Diego Biurrun <diego@biurrun.de>

libavcodec/dirac.c

@@ -58,6 +58,7 @@ static const dirac_source_params dirac_source_parameters_defaults[] = {
     { 7680, 4320, 1, 0, 1, 6,  1, 3840, 2160, 0, 0, 3, 3 },
 };
 
+/* [DIRAC_STD] Table 10.4 - Available preset pixel aspect ratio values */
 static const AVRational dirac_preset_aspect_ratios[] = {
     {1, 1},
     {10, 11},
@@ -67,11 +68,16 @@ static const AVRational dirac_preset_aspect_ratios[] = {
     {4, 3},
 };
 
+/* [DIRAC_STD] Values 9,10 of 10.3.5 Frame Rate.
+ * Table 10.3 Available preset frame rate values
+ */
 static const AVRational dirac_frame_rate[] = {
     {15000, 1001},
     {25, 2},
 };
 
+/* [DIRAC_STD] This should be equivalent to Table 10.5 Available signal
+ * range presets */
 static const struct {
     uint8_t             bitdepth;
     enum AVColorRange   color_range;
@@ -100,11 +106,14 @@ static const struct {
     { AVCOL_PRI_BT709,     AVCOL_SPC_BT709,   AVCOL_TRC_UNSPECIFIED /* DCinema */ },
 };
 
+/* [DIRAC_STD] Table 10.2 Supported chroma sampling formats + luma Offset */
 static const enum PixelFormat dirac_pix_fmt[2][3] = {
     { PIX_FMT_YUV444P,  PIX_FMT_YUV422P,  PIX_FMT_YUV420P  },
     { PIX_FMT_YUVJ444P, PIX_FMT_YUVJ422P, PIX_FMT_YUVJ420P },
 };
 
+/* [DIRAC_STD] 10.3 Parse Source Parameters.
+ * source_parameters(base_video_format) */
 static int parse_source_parameters(AVCodecContext *avctx, GetBitContext *gb,
                                    dirac_source_params *source)
 {
@@ -112,13 +121,18 @@ static int parse_source_parameters(AVCodecContext *avctx, GetBitContext *gb,
     unsigned luma_depth = 8, luma_offset = 16;
     int idx;
 
+    /* [DIRAC_STD] 10.3.2 Frame size. frame_size(video_params) */
+    /* [DIRAC_STD] custom_dimensions_flag */
     if (get_bits1(gb)) {
-        source->width  = svq3_get_ue_golomb(gb);
-        source->height = svq3_get_ue_golomb(gb);
+        source->width  = svq3_get_ue_golomb(gb); /* [DIRAC_STD] FRAME_WIDTH  */
+        source->height = svq3_get_ue_golomb(gb); /* [DIRAC_STD] FRAME_HEIGHT */
     }
 
-    // chroma subsampling
+    /* [DIRAC_STD] 10.3.3 Chroma Sampling Format.
+     *  chroma_sampling_format(video_params) */
+    /* [DIRAC_STD] custom_chroma_format_flag */
     if (get_bits1(gb))
+        /* [DIRAC_STD] CHROMA_FORMAT_INDEX */
         source->chroma_format = svq3_get_ue_golomb(gb);
     if (source->chroma_format > 2) {
         av_log(avctx, AV_LOG_ERROR, "Unknown chroma format %d\n",
@@ -126,34 +140,43 @@ static int parse_source_parameters(AVCodecContext *avctx, GetBitContext *gb,
         return AVERROR_INVALIDDATA;
     }
 
+    /* [DIRAC_STD] 10.3.4 Scan Format. scan_format(video_params) */
+    /* [DIRAC_STD] custom_scan_format_flag */
     if (get_bits1(gb))
+        /* [DIRAC_STD] SOURCE_SAMPLING */
         source->interlaced = svq3_get_ue_golomb(gb);
     if (source->interlaced > 1)
         return AVERROR_INVALIDDATA;
 
-    // frame rate
-    if (get_bits1(gb)) {
+    /* [DIRAC_STD] 10.3.5 Frame Rate. frame_rate(video_params) */
+    if (get_bits1(gb)) { /* [DIRAC_STD] custom_frame_rate_flag */
         source->frame_rate_index = svq3_get_ue_golomb(gb);
 
         if (source->frame_rate_index > 10)
             return AVERROR_INVALIDDATA;
 
         if (!source->frame_rate_index) {
+            /* [DIRAC_STD] FRAME_RATE_NUMER */
             frame_rate.num = svq3_get_ue_golomb(gb);
+            /* [DIRAC_STD] FRAME_RATE_DENOM */
             frame_rate.den = svq3_get_ue_golomb(gb);
         }
     }
+    /* [DIRAC_STD] preset_frame_rate(video_params, index) */
     if (source->frame_rate_index > 0) {
         if (source->frame_rate_index <= 8)
             frame_rate = avpriv_frame_rate_tab[source->frame_rate_index];
         else
+             /* [DIRAC_STD] Table 10.3 values 9-10 */
             frame_rate = dirac_frame_rate[source->frame_rate_index-9];
     }
     av_reduce(&avctx->time_base.num, &avctx->time_base.den,
               frame_rate.den, frame_rate.num, 1<<30);
 
-    // aspect ratio
-    if (get_bits1(gb)) {
+    /* [DIRAC_STD] 10.3.6 Pixel Aspect Ratio.
+     * pixel_aspect_ratio(video_params) */
+    if (get_bits1(gb)) { /* [DIRAC_STD] custom_pixel_aspect_ratio_flag */
+         /* [DIRAC_STD] index */
         source->aspect_ratio_index = svq3_get_ue_golomb(gb);
 
         if (source->aspect_ratio_index > 6)
@@ -164,19 +187,29 @@ static int parse_source_parameters(AVCodecContext *avctx, GetBitContext *gb,
             avctx->sample_aspect_ratio.den = svq3_get_ue_golomb(gb);
         }
     }
+    /* [DIRAC_STD] Take value from Table 10.4 Available preset pixel
+     *  aspect ratio values */
     if (source->aspect_ratio_index > 0)
         avctx->sample_aspect_ratio =
                 dirac_preset_aspect_ratios[source->aspect_ratio_index-1];
 
-    if (get_bits1(gb)) {
+    /* [DIRAC_STD] 10.3.7 Clean area. clean_area(video_params) */
+    if (get_bits1(gb)) { /* [DIRAC_STD] custom_clean_area_flag */
+        /* [DIRAC_STD] CLEAN_WIDTH */
         source->clean_width        = svq3_get_ue_golomb(gb);
+         /* [DIRAC_STD] CLEAN_HEIGHT */
         source->clean_height       = svq3_get_ue_golomb(gb);
+         /* [DIRAC_STD] CLEAN_LEFT_OFFSET */
         source->clean_left_offset  = svq3_get_ue_golomb(gb);
+        /* [DIRAC_STD] CLEAN_RIGHT_OFFSET */
         source->clean_right_offset = svq3_get_ue_golomb(gb);
     }
 
-    // Override signal range.
-    if (get_bits1(gb)) {
+    /* [DIRAC_STD] 10.3.8 Signal range. signal_range(video_params)
+     * WARNING: Some adaptation seems to be done using the
+     * AVCOL_RANGE_MPEG/JPEG values */
+    if (get_bits1(gb)) { /* [DIRAC_STD] custom_signal_range_flag */
+        /* [DIRAC_STD] index */
         source->pixel_range_index = svq3_get_ue_golomb(gb);
 
         if (source->pixel_range_index > 4)
@@ -186,12 +219,13 @@ static int parse_source_parameters(AVCodecContext *avctx, GetBitContext *gb,
         if (!source->pixel_range_index) {
             luma_offset = svq3_get_ue_golomb(gb);
             luma_depth  = av_log2(svq3_get_ue_golomb(gb))+1;
-            svq3_get_ue_golomb(gb); // chroma offset
-            svq3_get_ue_golomb(gb); // chroma excursion
-
+            svq3_get_ue_golomb(gb); /* chroma offset    */
+            svq3_get_ue_golomb(gb); /* chroma excursion */
             avctx->color_range = luma_offset ? AVCOL_RANGE_MPEG : AVCOL_RANGE_JPEG;
         }
     }
+    /* [DIRAC_STD] Table 10.5
+     * Available signal range presets <--> pixel_range_presets */
     if (source->pixel_range_index > 0) {
         idx                = source->pixel_range_index-1;
         luma_depth         = pixel_range_presets[idx].bitdepth;
@@ -203,8 +237,9 @@ static int parse_source_parameters(AVCodecContext *avctx, GetBitContext *gb,
 
     avctx->pix_fmt = dirac_pix_fmt[!luma_offset][source->chroma_format];
 
-    // color spec
-    if (get_bits1(gb)) {
+    /* [DIRAC_STD] 10.3.9 Colour specification. colour_spec(video_params) */
+    if (get_bits1(gb)) { /* [DIRAC_STD] custom_colour_spec_flag */
+         /* [DIRAC_STD] index */
         idx = source->color_spec_index = svq3_get_ue_golomb(gb);
 
         if (source->color_spec_index > 4)
@@ -215,12 +250,13 @@ static int parse_source_parameters(AVCodecContext *avctx, GetBitContext *gb,
         avctx->color_trc       = dirac_color_presets[idx].color_trc;
 
         if (!source->color_spec_index) {
+            /* [DIRAC_STD] 10.3.9.1 Colour primaries */
             if (get_bits1(gb)) {
                 idx = svq3_get_ue_golomb(gb);
                 if (idx < 3)
                     avctx->color_primaries = dirac_primaries[idx];
             }
-
+            /* [DIRAC_STD] 10.3.9.2 Colour matrix */
             if (get_bits1(gb)) {
                 idx = svq3_get_ue_golomb(gb);
                 if (!idx)
@@ -228,7 +264,7 @@ static int parse_source_parameters(AVCodecContext *avctx, GetBitContext *gb,
                 else if (idx == 1)
                     avctx->colorspace = AVCOL_SPC_BT470BG;
             }
-
+            /* [DIRAC_STD] 10.3.9.3 Transfer function */
             if (get_bits1(gb) && !svq3_get_ue_golomb(gb))
                 avctx->color_trc = AVCOL_TRC_BT709;
         }
@@ -242,6 +278,7 @@ static int parse_source_parameters(AVCodecContext *avctx, GetBitContext *gb,
     return 0;
 }
 
+/* [DIRAC_STD] 10. Sequence Header. sequence_header() */
 int avpriv_dirac_parse_sequence_header(AVCodecContext *avctx, GetBitContext *gb,
                                    dirac_source_params *source)
 {
@@ -249,10 +286,13 @@ int avpriv_dirac_parse_sequence_header(AVCodecContext *avctx, GetBitContext *gb,
     unsigned video_format, picture_coding_mode;
     int ret;
 
+    /* [DIRAC_SPEC] 10.1 Parse Parameters. parse_parameters() */
     version_major  = svq3_get_ue_golomb(gb);
     svq3_get_ue_golomb(gb); /* version_minor */
     avctx->profile = svq3_get_ue_golomb(gb);
     avctx->level   = svq3_get_ue_golomb(gb);
+    /* [DIRAC_SPEC] sequence_header() -> base_video_format as defined in
+     * 10.2 Base Video Format, table 10.1 Dirac predefined video formats */
     video_format   = svq3_get_ue_golomb(gb);
 
     if (version_major < 2)
@@ -266,7 +306,8 @@ int avpriv_dirac_parse_sequence_header(AVCodecContext *avctx, GetBitContext *gb,
     // Fill in defaults for the source parameters.
     *source = dirac_source_parameters_defaults[video_format];
 
-    // Override the defaults.
+    /* [DIRAC_STD] 10.3 Source Parameters
+     * Override the defaults. */
     if (ret = parse_source_parameters(avctx, gb, source))
         return ret;
 
@@ -275,7 +316,8 @@ int avpriv_dirac_parse_sequence_header(AVCodecContext *avctx, GetBitContext *gb,
 
     avcodec_set_dimensions(avctx, source->width, source->height);
 
-    // currently only used to signal field coding
+    /* [DIRAC_STD] picture_coding_mode shall be 0 for fields and 1 for frames
+     * currently only used to signal field coding */
     picture_coding_mode = svq3_get_ue_golomb(gb);
     if (picture_coding_mode != 0) {
         av_log(avctx, AV_LOG_ERROR, "Unsupported picture coding mode %d",