Added arn to the main repository

arn/video/Info.go

@@ -0,0 +1,87 @@
+package video
+
+import (
+	"os"
+	"strings"
+	"time"
+
+	"github.com/akyoto/go-matroska/matroska"
+)
+
+// Info includes some general information about the video file.
+type Info struct {
+	Duration time.Duration `json:"duration"`
+	FileSize int64         `json:"fileSize"`
+	Video    videoInfo     `json:"video"`
+	Audio    audioInfo     `json:"audio"`
+}
+
+type videoInfo struct {
+	Width  int     `json:"width"`
+	Height int     `json:"height"`
+	FPS    float64 `json:"fps"`
+	Codec  string  `json:"codec"`
+}
+
+type audioInfo struct {
+	BitDepth          int     `json:"bitDepth"`
+	SamplingFrequency float64 `json:"samplingFrequency"`
+	Channels          int     `json:"channels"`
+	Codec             string  `json:"codec"`
+}
+
+// GetInfo returns the information about the given video file.
+func GetInfo(file string) (*Info, error) {
+	stat, err := os.Stat(file)
+
+	if err != nil {
+		return nil, err
+	}
+
+	doc, err := matroska.Decode(file)
+
+	if err != nil {
+		return nil, err
+	}
+
+	video := doc.Segment.Tracks[0].Entries[0]
+	audio := doc.Segment.Tracks[0].Entries[1]
+	frameDuration := video.DefaultDuration
+	fps := 1.0 / frameDuration.Seconds()
+	duration := time.Duration(doc.Segment.Info[0].Duration) * doc.Segment.Info[0].TimecodeScale
+	videoCodecID := normalizeCodecID(video.CodecID)
+	audioCodecID := normalizeCodecID(audio.CodecID)
+
+	info := &Info{
+		Duration: duration,
+		FileSize: stat.Size(),
+
+		Video: videoInfo{
+			Width:  video.Video.Width,
+			Height: video.Video.Height,
+			FPS:    fps,
+			Codec:  videoCodecID,
+		},
+
+		Audio: audioInfo{
+			BitDepth:          audio.Audio.BitDepth,
+			SamplingFrequency: audio.Audio.SamplingFreq,
+			Channels:          audio.Audio.Channels,
+			Codec:             audioCodecID,
+		},
+	}
+
+	return info, nil
+}
+
+func normalizeCodecID(codecID string) string {
+	if strings.HasPrefix(codecID, "V_") {
+		codecID = strings.TrimPrefix(codecID, "V_")
+	}
+
+	if strings.HasPrefix(codecID, "A_") {
+		codecID = strings.TrimPrefix(codecID, "A_")
+	}
+
+	return strings.ToLower(codecID)
+}