lavc/av1_parser: Extract SAR from render_size

Extract the Sample Aspect Ratio (SAR) from render_width_minus_1 and
render_height_minus_1 in the sequence header.

The AV1 specification defines the render dimensions, which can be used
in conjunction with the coded dimensions to determine the pixel aspect
ratio. This ensures consistent aspect ratio handling for AV1 streams
encapsulated in containers like MP4 or MKV, as observed in the updated
FATE tests where SAR changes from 0/1 to 1/1.

Signed-off-by: Jun Zhao <barryjzhao@tencent.com>

libavcodec/av1_parser.c

@@ -134,6 +134,13 @@ static int av1_parser_parse(AVCodecParserContext *ctx,
             break;
         }
         ctx->picture_structure = AV_PICTURE_STRUCTURE_FRAME;
+
+        /* Extract SAR from render_height_minus_1 & render_width_minus_1 */
+        av_reduce(&avctx->sample_aspect_ratio.num,
+                  &avctx->sample_aspect_ratio.den,
+                  (int64_t)ctx->height * (frame->render_width_minus_1  + 1),
+                  (int64_t)ctx->width  * (frame->render_height_minus_1 + 1),
+                  INT_MAX);
     }
 
     switch (av1->bit_depth) {

tests/ref/fate/av1-annexb-demux

@@ -3,7 +3,7 @@
 #media_type 0: video
 #codec_id 0: av1
 #dimensions 0: 300x300
-#sar 0: 0/1
+#sar 0: 1/1
 0,          0,          0,    48000,    12691, 0xf0adcc79
 0,      48000,      48000,    48000,     4975, 0x1742a45f, F=0x0
 0,      96000,      96000,    48000,      928, 0x7408be1a, F=0x0

tests/ref/fate/enhanced-flv-av1

@@ -3,7 +3,7 @@
 #media_type 0: video
 #codec_id 0: av1
 #dimensions 0: 320x176
-#sar 0: 0/1
+#sar 0: 1/1
 0,          0,          0,       41,     4718, 0xc4d912ec
 0,         42,         42,       41,     5109, 0xc065dd7d, F=0x0
 0,         83,         83,       41,      192, 0x160c5335, F=0x0

tests/ref/fate/enhanced-flv-multitrack

@@ -31,7 +31,7 @@
 #media_type 4: video
 #codec_id 4: av1
 #dimensions 4: 1920x1080
-#sar 4: 0/1
+#sar 4: 1/1
 #tb 5: 1/1000
 #media_type 5: audio
 #codec_id 5: flac

tests/ref/lavf-fate/av1.mkv

@@ -1,3 +1,3 @@
-d875b42964dd55c8cea2e2752379d327 *tests/data/lavf-fate/lavf.av1.mkv
-55660 tests/data/lavf-fate/lavf.av1.mkv
+ba198efa114b4db3c9f772728f84978b *tests/data/lavf-fate/lavf.av1.mkv
+55656 tests/data/lavf-fate/lavf.av1.mkv
 tests/data/lavf-fate/lavf.av1.mkv CRC=0x7c27cc15

tests/ref/lavf-fate/av1.mp4

@@ -1,3 +1,3 @@
-194cd796f3d28a890b516b2507f57180 *tests/data/lavf-fate/lavf.av1.mp4
-55960 tests/data/lavf-fate/lavf.av1.mp4
+d6afef355cf1bcf1a71b9cfb98c32fba *tests/data/lavf-fate/lavf.av1.mp4
+55976 tests/data/lavf-fate/lavf.av1.mp4
 tests/data/lavf-fate/lavf.av1.mp4 CRC=0x7c27cc15