Update Readme

README.md

@@ -7,32 +7,98 @@ MP3/MP4/FLAC/OGG tag reader and writer for go
 [![Go Reference](https://pkg.go.dev/badge/github.com/gcottom/audiometa/v2.svg)](https://pkg.go.dev/github.com/gcottom/audiometa/v2)   [![Go Report Card](https://goreportcard.com/badge/github.com/gcottom/audiometa/v2)](https://goreportcard.com/report/github.com/gcottom/audiometa/v2)   [![Coverage Status](https://coveralls.io/repos/github/gcottom/audiometa/badge.svg?branch=main)](https://coveralls.io/github/gcottom/audiometa?branch=main)
 
 
-This package allows you to parse and write ID tags for mp3, mp4 (m4a, m4b, m4p), FLAC, and ogg (Vorbis, OPUS) files.
-
-This is the only package available in Go that uses native Go to allow writing of ogg vorbis metadata. As an added bonus I've added support for ogg OPUS as well.
-
-You can access all of the fields of the IDTag through the accessor functions.
-
-v2 massively improves memory management and speed. Several sections have been rewritten. 
-
-
-Fields that can be parsed:
-
-MP3: Artist, AlbumArtist, Album, AlbumArt, Comments, Composer, Genre, Title, Year, BPM, ContentType, CopyrightMessage, Date, EncodedBy, Lyricist, FileType, Language, Length, PartOfSet, and Publisher
-
-MP4: Artist, AlbumArtist, Album, AlbumArt, Comments, Composer, Genre, Title, Year, EncodedBy, and CopyrightMessage
-
-FLAC: Artist, Album, AlbumArt, Date, Genre Title
-
-OGG: Artist, AlbumArtist, Album, AlbumArt, Comment, Date, Genre, Title, Copyright, Publisher, Composer, and has extended support for all other custom or unmapped fields
-
-
-Fields that can be written: 
-
-MP3: Artist, AlbumArtist, Album, AlbumArt, Comments, Composer, Genre, Title, Year, BPM, ContentType, CopyrightMessage, Date, EncodedBy, Lyricist, FileType, Language, Length, PartOfSet, and Publisher
-
-MP4: Artist, AlbumArtist, Album, AlbumArt, Comments, Composer, Genre, Title, Year, and CopyrightMessage
-
-FLAC: Artist, Album, AlbumArt, Genre, Title
-
-OGG: Artist, AlbumArtist, Album, AlbumArt, Comment, Date, Genre, Title, Copyright, Publisher, Composer, and has extended support to allow for passthrough of unknown fields and adding any custom or unmapped field
+This package enables parsing and writing of ID tags for mp3, mp4 (m4a, m4b, m4p), FLAC, and ogg (Vorbis, OPUS) files.
+
+All fields can be accessed via the provided accessor methods. Only supported fields per file type will return non zero data. The exception to this is that ogg files support a passthrough map. 
+By setting kv pairs in the passthrough map, non-standard vorbis comment tags can be written to both ogg Vorbis and ogg OPUS files. 
+
+
+# Parsable Fields Per FileType 
+
+## MP3
+Artist, AlbumArtist, Album, AlbumArt, BPM, ContentType, Comments, Composer, CopyrightMessage, Date, EncodedBy, FileType, Genre, Language, Length, Lyricist, PartOfSet, Publisher, Title, Year
+
+## MP4 & MP4 Types (m4a, m4b, m4p, mp4)
+Artist, AlbumArtist, Album, AlbumArt, Comments, Composer, CopyrightMessage, EncodedBy, Genre, Title, Year
+
+## FLAC
+Artist, Album, AlbumArt, Date, Genre, Title
+
+## OGG (Vorbis and OPUS within an ogg container)
+Artist, AlbumArtist, Album, AlbumArt, Comment, Composer, Copyright, Date, Genre, Title, Publisher, (extended support for custom fields via passthrough map)
+
+
+# Writable Fields Per FileType
+
+## MP3
+Artist, AlbumArtist, Album, AlbumArt, BPM, ContentType, Comments, Composer, CopyrightMessage, Date, EncodedBy, FileType, Genre, Language, Length, Lyricist, PartOfSet, Publisher, Title, Year
+
+## MP4 & MP4 Types (m4a, m4b, m4p, mp4)
+Artist, AlbumArtist, Album, Comments, CopyrightMessage, Composer, Genre, Title, Year (AlbumArt is currently not writeable)
+
+## FLAC
+Artist, Album, AlbumArt, Date, Genre, Title
+
+## OGG (Vorbis and OPUS within an ogg container)
+Artist, AlbumArtist, Album, AlbumArt, Comment, Composer, Copyright, Date, Genre, Title, Publisher, (extended support for custom fields via passthrough map)
+
+# Usage
+
+## Open Tag For Reading From Path
+```
+tag, err := audiometa.OpenTagFromPath("./my-audio-file.mp3")
+if err != nil{
+    panic(err)
+}
+
+artist := tag.Artist()
+album := tag.Album()
+title := tag.Title()
+```
+
+## Open Tag For Reading From io.ReadSeeker
+```
+f, err := os.Open("./my-audio-file.mp3")
+tag, err := audiometa.Open(f, audiometa.ParseOptions{Format: audiometa.MP3}) //ParseOptions is only required if the file does not have an extension
+if err != nil{
+    panic(err)
+}
+
+artist := tag.Artist()
+album := tag.Album()
+title := tag.Title()
+```
+
+## Update Tag
+```
+f, err := os.Open("./my-audio-file.mp3")
+if err != nil{
+    panic(err)
+}
+tag, err := audiometa.Open(f)
+if err != nil{
+    panic(err)
+}
+tag.SetArtist("Beyonce")
+err = tag.Save(f)
+if err != nil{
+    panic(err)
+}
+```
+
+## Clear All Tags And Save
+```
+f, err := os.Open("./my-audio-file.mp3")
+if err != nil{
+    panic(err)
+}
+tag, err := audiometa.Open(f)
+if err != nil{
+    panic(err)
+}
+tag.ClearAllTags()
+err = tag.Save(f)
+if err != nil{
+    panic(err)
+}
+```

mp4_decoder.go

@@ -40,9 +40,6 @@ var atoms = atomNames(map[string]string{
 	"disk":    "disc",
 })
 
-// Detect PNG image if "implicit" class is used
-var pngHeader = []byte{137, 80, 78, 71, 13, 10, 26, 10}
-
 type atomNames map[string]string
 
 func (f atomNames) name(n string) []string {
@@ -164,9 +161,7 @@ func (m metadataMP4) readAtomData(r io.ReadSeeker, name string, size uint32, pro
 
 	if contentType == "implicit" {
 		if name == "covr" {
-			if bytes.HasPrefix(b, pngHeader) {
-				contentType = "png"
-			}
+			contentType = "png"
 		}
 	}