mirror of https://github.com/jlelse/GoBlog
78 lines
1.7 KiB
Go
78 lines
1.7 KiB
Go
package mp3merge
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import (
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"bytes"
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"errors"
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"io"
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"github.com/dmulholl/mp3lib"
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)
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// Inspired by https://github.com/dmulholl/mp3cat/blob/2ec1e4fe4d995ebd41bf1887b3cab8e2a569b3d4/mp3cat.go
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// Merge multiple mp3s into one mp3.
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func MergeMP3(out io.Writer, in ...io.Reader) error {
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if len(in) == 0 {
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return errors.New("no inputs specified")
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}
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var totalFrames, totalBytes uint32
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var firstBitRate int
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var isVBR bool
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var tmpOut bytes.Buffer
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// Loop over the input files and append their MP3 frames to the output file.
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for _, inReader := range in {
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if inReader == nil {
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return errors.New("nil input")
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}
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isFirstFrame := true
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for {
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// Read the next frame from the input
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frame := mp3lib.NextFrame(inReader)
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if frame == nil {
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break
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}
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// Skip the first frame if it's a VBR header
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if isFirstFrame {
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isFirstFrame = false
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if mp3lib.IsXingHeader(frame) || mp3lib.IsVbriHeader(frame) {
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continue
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}
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}
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// If we detect more than one bitrate we'll need to add a VBR header to the output
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if firstBitRate == 0 {
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firstBitRate = frame.BitRate
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} else if frame.BitRate != firstBitRate {
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isVBR = true
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}
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// Write the frame to the temporary output
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_, err := tmpOut.Write(frame.RawBytes)
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if err != nil {
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return err
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}
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// Increment the total number of frames and bytes
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totalFrames += 1
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totalBytes += uint32(len(frame.RawBytes))
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}
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}
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// If we detected multiple bitrates, prepend a VBR header to the output
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if isVBR {
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xingHeader := mp3lib.NewXingHeader(totalFrames, totalBytes)
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_, err := out.Write(xingHeader.RawBytes)
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if err != nil {
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return err
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}
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}
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// Copy the temporary output to the output
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_, err := tmpOut.WriteTo(out)
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return err
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}
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