codecs: Add support for extradata output from ffprobe (-show_data)

Author: codedread

codecs/codecs.js

@@ -197,13 +197,33 @@ export function getFullMIMEString(info) {
 
 // TODO: Consider whether any of these should be exported.
 
+function getCleanHex(extradata) {
+  // 1. Split into lines
+  // 2. Extract only the middle hex section (after ':' and before '  ')
+  // 3. Remove all spaces
+  return extradata.split('\n')
+    .map(line => line.split(':')[1]?.split('  ')[0])
+    .filter(Boolean)
+    .join('')
+    .replace(/\s/g, '');
+}
+
 /**
  * AVC1 is the same thing as H264.
  * https://developer.mozilla.org/en-US/docs/Web/Media/Formats/codecs_parameter#iso_base_media_file_format_mp4_quicktime_and_3gp
  * @param {ProbeStream} stream
  * @returns {string}
  */
 function getAVC1CodecString(stream) {
+  if (stream.extradata && stream.codec_tag_string === 'avc1') {
+    const hex = getCleanHex(stream.extradata); // results in "014d4028..."
+
+    // Bytes 1, 2, and 3 are the Profile, Constraints, and Level.
+    // In the hex string, these are characters at index 2 through 8.
+    const codecPart = hex.substring(2, 8).toUpperCase();
+    return `avc1.${codecPart}`;
+  }
+
   if (!stream.profile) throw `No profile found in AVC1 stream`;
 
   let frag = 'avc1';

docs/unrar.html

@@ -271,6 +271,32 @@ describe('codecs test suite', () => {
             .to.be.a('string')
             .and.satisfy(s => s.startsWith('video/mp4; codecs="avc1.4D00'));
       });
+
+      describe('extradata tests', () => {
+        it('prefers extradata for codec string', () => {
+          info.streams[0].extradata = '00000000: 014d 4028 ffe1 001a 674d 4028 9a66 0140 .M@(...gM@(.f.@';
+          expect(getFullMIMEString(info))
+              .equals('video/mp4; codecs="avc1.4D4028"');
+        });
+
+        it('handles multiline extradata', () => {
+          info.streams[0].extradata =
+              '00000000: 0164 0029 ffe1 001b 6764 0029 ac2b 4028 .d.)....gd.).+@(\n' +
+              '00000010: 2f82 1801 1000 0003 0010 0000 0303 20f1 /............. .';
+          expect(getFullMIMEString(info))
+              .equals('video/mp4; codecs="avc1.640029"');
+        });
+
+        it('does not use extradata if codec_tag_string is not avc1', () => {
+          info.streams[0].codec_tag_string = 'not-avc1';
+          info.streams[0].codec_name = 'h264';
+          info.streams[0].profile = 'Main';
+          info.streams[0].level = 20;
+          info.streams[0].extradata = '00000000: 014d 4028 ffe1 001a 674d 4028 9a66 0140 .M@(...gM@(.f.@';
+          expect(getFullMIMEString(info))
+              .equals('video/mp4; codecs="avc1.4D0014"');
+        });
+      });
     });
   });