main: changes, fixes

- refactors http session usage across modules
- adjusts video info extraction
- improves temporary directory, concurrency limits, buffering, and error handling in download routines

util/av/thumbnail.go

@@ -12,10 +12,7 @@ func ExtractVideoThumbnail(
 		Input(videoPath).
 		Output(thumbnailPath, ffmpeg.KwArgs{
 			"vframes": 1,
-			"f":       "image2",
 			"ss":      "00:00:01",
-			"c:v":     "mjpeg",
-			"q:v":     10, // not sure
 		}).
 		Silent(true).
 		OverWriteOutput().

util/av/videoinfo.go

@@ -10,9 +10,9 @@ func GetVideoInfo(filePath string) (int64, int64, int64) {
 	if err != nil {
 		return 0, 0, 0
 	}
-	duration := gjson.Get(probeData, "format.duration").Int()
+	duration := gjson.Get(probeData, "format.duration").Float()
 	width := gjson.Get(probeData, "streams.0.width").Int()
 	height := gjson.Get(probeData, "streams.0.height").Int()
 
-	return duration, width, height
+	return int64(duration), width, height
 }