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fq/format/vorbis/vorbis_comment.go

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package vorbis
import (
"encoding/base64"
"io"
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"strings"
"github.com/wader/fq/format"
"github.com/wader/fq/format/registry"
"github.com/wader/fq/pkg/decode"
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)
var flacPicture decode.Group
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func init() {
registry.MustRegister(decode.Format{
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Name: format.VORBIS_COMMENT,
Description: "Vorbis comment",
DecodeFn: commentDecode,
Dependencies: []decode.Dependency{
{Names: []string{format.FLAC_PICTURE}, Group: &flacPicture},
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},
})
}
func commentDecode(d *decode.D, in any) any {
d.Endian = decode.LittleEndian
vendorLen := d.FieldU32("vendor_length")
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d.FieldUTF8("vendor", int(vendorLen))
userCommentListLength := d.FieldU32("user_comment_list_length")
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i := uint64(0)
d.FieldStructArrayLoop("user_comments", "user_comment", func() bool { return i < userCommentListLength }, func(d *decode.D) {
userCommentLength := d.FieldU32("length")
userCommentStart := d.Pos()
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userComment := d.FieldUTF8("comment", int(userCommentLength))
var metadataBlockPicturePrefix = "METADATA_BLOCK_PICTURE="
var metadataBlockPicturePrefixLower = "metadata_block_picture="
if strings.HasPrefix(userComment, metadataBlockPicturePrefix) ||
strings.HasPrefix(userComment, metadataBlockPicturePrefixLower) {
base64Offset := int64(len(metadataBlockPicturePrefix)) * 8
base64Len := int64(len(userComment))*8 - base64Offset
_, base64Br, dv, _, _ := d.TryFieldReaderRangeFormat(
"picture",
userCommentStart+base64Offset, base64Len,
func(r io.Reader) io.Reader { return base64.NewDecoder(base64.StdEncoding, r) },
flacPicture, nil,
)
if dv == nil && base64Br != nil {
d.FieldRootBitBuf("picture", base64Br)
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}
}
i++
})
return nil
}