mp4: Decode emsg box

Author: wader

format/mp4/boxes.go

@@ -1741,6 +1741,35 @@ func decodeBox(ctx *decodeContext, d *decode.D, typ string) {
 		default:
 			d.FieldRawLen("data", d.BitsLeft())
 		}
+	case "emsg":
+		// https://aomediacodec.github.io/id3-emsg/
+		version := d.FieldU8("version")
+		d.FieldU24("flags")
+		var schemeIdUri string
+		switch version {
+		case 0:
+			schemeIdUri = d.FieldUTF8Null("scheme_id_uri")
+			d.FieldUTF8Null("value")
+			d.FieldU32("timescale")
+			d.FieldU32("presentation_time_delta")
+			d.FieldU32("event_duration")
+			d.FieldU32("id")
+		case 1:
+			d.FieldU32("timescale")
+			d.FieldU64("presentation_time")
+			d.FieldU32("event_duration")
+			d.FieldU32("id")
+			schemeIdUri = d.FieldUTF8Null("scheme_id_uri")
+			d.FieldUTF8Null("value")
+		default:
+			d.FieldRawLen("data", d.BitsLeft())
+		}
+		switch schemeIdUri {
+		case "https://aomedia.org/emsg/ID3":
+			d.FieldFormat("message_data", &id3v2Group, nil)
+		default:
+			d.FieldRawLen("message_data", d.BitsLeft())
+		}
 	default:
 		// there are at least 4 ways to encode udta metadata in mov/mp4 files.
 		//

format/mp4/testdata/emsg.fqtest

@@ -0,0 +1,20 @@
+$ fq -o force=true -d mp4 dv emsg.mp4
+     |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|0123456789abcdef|.{}: emsg.mp4 (mp4) 0x0-0x1a0.7 (417)
+     |                                               |                |  boxes[0:1]: 0x0-0x1a0.7 (417)
+     |                                               |                |    [0]{}: box 0x0-0x1a0.7 (417)
+0x000|00 00 01 a1                                    |....            |      size: 417 0x0-0x3.7 (4)
+0x000|            65 6d 73 67                        |    emsg        |      type: "emsg" (Event message) 0x4-0x7.7 (4)
+0x000|                        00                     |        .       |      version: 0 0x8-0x8.7 (1)
+0x000|                           00 00 00            |         ...    |      flags: 0 0x9-0xb.7 (3)
+0x000|                                    68 74 74 70|            http|      scheme_id_uri: "http://youtube.com/streaming/metadata/segment/1..." 0xc-0x40.7 (53)
+0x010|3a 2f 2f 79 6f 75 74 75 62 65 2e 63 6f 6d 2f 73|://youtube.com/s|
+*    |until 0x40.7 (53)                              |                |
+0x040|   00                                          | .              |      value: "" 0x41-0x41.7 (1)
+0x040|      00 00 00 01                              |  ....          |      timescale: 1 0x42-0x45.7 (4)
+0x040|                  00 00 00 00                  |      ....      |      presentation_time_delta: 0 0x46-0x49.7 (4)
+0x040|                              00 00 00 00      |          ....  |      event_duration: 0 0x4a-0x4d.7 (4)
+0x040|                                          30 d7|              0.|      id: 819396933 0x4e-0x51.7 (4)
+0x050|01 45                                          |.E              |
+0x050|      53 65 71 75 65 6e 63 65 2d 4e 75 6d 62 65|  Sequence-Numbe|      message_data: raw bits 0x52-0x1a0.7 (335)
+0x060|72 3a 20 30 0d 0a 49 6e 67 65 73 74 69 6f 6e 2d|r: 0..Ingestion-|
+*    |until 0x1a0.7 (end) (335)                      |                |