[__init__] Metadata should be added after conversion

Fixes #5594

ChangeLog

 version <unreleased>
 
+Core
+* [__init__] Metadata are now added after conversion (#5594)
+
+
 Extractors
 * [openload] Fix extraction (#10408, #12357)
 

youtube_dl/__init__.py

@@ -242,14 +242,11 @@ def _real_main(argv=None):
 
     # PostProcessors
     postprocessors = []
-    # Add the metadata pp first, the other pps will copy it
     if opts.metafromtitle:
         postprocessors.append({
             'key': 'MetadataFromTitle',
             'titleformat': opts.metafromtitle
         })
-    if opts.addmetadata:
-        postprocessors.append({'key': 'FFmpegMetadata'})
     if opts.extractaudio:
         postprocessors.append({
             'key': 'FFmpegExtractAudio',
@@ -279,6 +276,11 @@ def _real_main(argv=None):
         })
         if not already_have_thumbnail:
             opts.writethumbnail = True
+    # FFmpegMetadataPP should be run after FFmpegVideoConvertorPP and
+    # FFmpegExtractAudioPP as containers before conversion may not support
+    # metadata (3gp, webm, etc.)
+    if opts.addmetadata:
+        postprocessors.append({'key': 'FFmpegMetadata'})
     # XAttrMetadataPP should be run after post-processors that may change file
     # contents
     if opts.xattrs: