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Added comments and links to ogg spec. Clarified code with const

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Simon L 2015-05-20 13:43:08 +02:00 committed by David Howden
parent 109d54c374
commit 01fd433fb4
1 changed files with 21 additions and 4 deletions
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25
ogg.go
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@ -10,8 +10,14 @@ import (
"os"
)
const (
idType int = 1
commentType = 3
)
// ReadOGGTags reads OGG metadata from the io.ReadSeeker, returning the resulting
// metadata in a Metadata implementation, or non-nil error if there was a problem.
// See http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html and http://www.xiph.org/ogg/doc/framing.html for details
// TODO: Needs a more generic return type than "metadataFLAC" and the "FLAC" format is not as obvious as "Vorbis comment"
func ReadOGGTags(r io.ReadSeeker) (Metadata, error) {
_, err := r.Seek(0, os.SEEK_SET)
@ -27,6 +33,8 @@ func ReadOGGTags(r io.ReadSeeker) (Metadata, error) {
return nil, errors.New("expected 'OggS'")
}
// Skip 22 bytes of Page header to read page_segments length byte at position 26
// See http://www.xiph.org/ogg/doc/framing.html
_, err = r.Seek(22, os.SEEK_CUR)
if err != nil {
return nil, err
@ -37,24 +45,30 @@ func ReadOGGTags(r io.ReadSeeker) (Metadata, error) {
return nil, err
}
// Seek and discard the segments
_, err = r.Seek(int64(nS), os.SEEK_CUR)
if err != nil {
return nil, err
}
idComment, err := readInt(r, 1)
// First packet type is identification, type 1
t, err := readInt(r, 1)
if err != nil {
return nil, err
}
if idComment != 1 {
if t != idType {
return nil, errors.New("expected 'vorbis' identification type 1")
}
// Seek and discard 29 bytes from common and identification header
// See http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html#x1-610004.2
_, err = r.Seek(29, os.SEEK_CUR)
if err != nil {
return nil, err
}
// Beginning of a new page. Comment packet is on a separate page
// See http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html#x1-132000A.2
oggs, err = readString(r, 4)
if err != nil {
return nil, err
@ -63,6 +77,7 @@ func ReadOGGTags(r io.ReadSeeker) (Metadata, error) {
return nil, errors.New("expected 'OggS'")
}
// Skip page 2 header, same as line 30
_, err = r.Seek(22, os.SEEK_CUR)
if err != nil {
return nil, err
@ -78,14 +93,16 @@ func ReadOGGTags(r io.ReadSeeker) (Metadata, error) {
return nil, err
}
typeComment, err := readInt(r, 1)
// Packet type is comment, type 3
t, err = readInt(r, 1)
if err != nil {
return nil, err
}
if typeComment != 3 {
if t != commentType {
return nil, errors.New("expected 'vorbis' comment type 3")
}
// Seek and discard 6 bytes from common header
_, err = r.Seek(6, os.SEEK_CUR)
if err != nil {
return nil, err