diff --git a/cli/cli.go b/cli/cli.go
index ef1f7c5..5030f27 100644
--- a/cli/cli.go
+++ b/cli/cli.go
@@ -3,7 +3,6 @@
 package main
 
 import (
-	"errors"
 	"flag"
 	"fmt"
 	"os"
@@ -50,12 +49,11 @@ var Arguments struct {
 	Help bool `json:"-"`
 	VideoInfo bool `json:"-"`
 	ListFormats bool `json:"-"`
-	UnparsedChapterNum   int  `json:"chapter_num"`
+	ChapterNum   int  `json:"chapter_num"`
 	// Parsed
 	Video core.GtvVideo `json:"-"`
 	StartDuration time.Duration `json:"-"`
 	StopDuration time.Duration `json:"-"`
-	ChapterIdx int `json:"-"`
 	Ratelimit float64 `json:"-"`
 }
 
@@ -91,7 +89,7 @@ func CliParseArguments() error {
 	flag.BoolVar(&Arguments.Help, "help", false, "")
 	flag.BoolVar(&Arguments.VideoInfo, "info", false, "")
 	flag.StringVar(&Arguments.Url, "url", "", "")
-	flag.IntVar(&Arguments.UnparsedChapterNum, "chapter", 0, "") // 0 -> chapter idx -1 -> complete stream
+	flag.IntVar(&Arguments.ChapterNum, "chapter", 0, "") // 0 -> chapter idx -1 -> complete stream
 	flag.StringVar(&Arguments.FormatName, "format", "auto", "")
 	flag.StringVar(&Arguments.OutputFile, "output", "", "")
 	flag.StringVar(&Arguments.TimestampStart, "start", "", "")
@@ -104,9 +102,6 @@ func CliParseArguments() error {
 	if err != nil {
 		return err
 	}
-	if Arguments.Video.Category != "streams" {
-		return errors.New("video category '" + Arguments.Video.Category + "' not supported")
-	}
 	if Arguments.TimestampStart == "" {
 		Arguments.StartDuration = -1
 	} else {
@@ -123,10 +118,9 @@ func CliParseArguments() error {
 			return err
 		}
 	}
-	Arguments.ChapterIdx = Arguments.UnparsedChapterNum - 1
 	Arguments.Ratelimit = ratelimitMbs * 1_000_000.0 // MB/s -> B/s
 	if Arguments.Ratelimit <= 0 {
-		return errors.New("the value of --max-rate must be greater than 0")
+		return &GenericCliAgumentError{Msg: "the value of --max-rate must be greater than 0"}
 	}
 	return err
 }
@@ -162,13 +156,16 @@ func CliRun() int {
 	fmt.Print("\n")
 	fmt.Printf("Title:     %s\n", streamEp.Title)
 	// Check and list chapters/formats and exit
-	if Arguments.ChapterIdx >= 0 {
-		if Arguments.ChapterIdx >= len(streamEp.Chapters) {
-			CliErrorMessage(&core.ChapterNotFoundError{ChapterNum: Arguments.UnparsedChapterNum})
-			CliAvailableChapters(streamEp.Chapters)
-			return 1
-		}
+	targetChapter, err := streamEp.GetChapterByNumber(Arguments.ChapterNum)
+	if err != nil {
+		CliErrorMessage(err)
+		CliAvailableChapters(streamEp.Chapters)
+		return 1
 	}
+	if Arguments.ChapterNum > 0 && len(streamEp.Chapters) > 0 {
+		fmt.Printf("Chapter:   %v. %v\n", Arguments.ChapterNum, targetChapter.Title)
+	}
+	// Video Info
 	if Arguments.VideoInfo {
 		fmt.Printf("Episode:   %s\n", streamEp.Episode)
 		fmt.Printf("Length:    %s\n", streamEp.Length)
@@ -198,22 +195,16 @@ func CliRun() int {
 		return 1
 	}
 	fmt.Printf("Format:    %v\n", format.Name)
-	// chapter
-	targetChapter := core.Chapter{Index: -1} // set Index to -1 for noop
-	if len(streamEp.Chapters) > 0 && Arguments.ChapterIdx >= 0 {
-		targetChapter = streamEp.Chapters[Arguments.ChapterIdx]
-		fmt.Printf("Chapter:   %v. %v\n", Arguments.UnparsedChapterNum, targetChapter.Title)
-	}
 	// We already set the output file correctly so we can output it
 	if Arguments.OutputFile == "" {
-		Arguments.OutputFile = streamEp.GetProposedFilename(Arguments.ChapterIdx)
+		Arguments.OutputFile = streamEp.GetProposedFilename(targetChapter)
 	}
 	// Start Download
 	fmt.Printf("Output:    %v\n", Arguments.OutputFile)
 	fmt.Print("\n")
 	successful := false
 	aborted := false
-	for p := range core.DownloadEpisode(
+	for p := range core.DownloadStreamEpisode(
 		streamEp,
 		targetChapter,
 		Arguments.FormatName,
@@ -242,7 +233,7 @@ func CliRun() int {
 		fmt.Print("\nAborted.                                                ")
 		return 130
 	} else if !successful {
-		CliErrorMessage(errors.New("download failed"))
+		CliErrorMessage(&GenericDownloadError{})
 		return 1
 	} else { return 0 }
 }
diff --git a/cli/errors.go b/cli/errors.go
new file mode 100644
index 0000000..941ac6f
--- /dev/null
+++ b/cli/errors.go
@@ -0,0 +1,15 @@
+package main
+
+type GenericCliAgumentError struct {
+	Msg string
+}
+
+func (err *GenericCliAgumentError) Error() string {
+	return err.Msg
+}
+
+type GenericDownloadError struct {}
+
+func (err *GenericDownloadError) Error() string {
+	return "download failed"
+}
diff --git a/core/errors.go b/core/errors.go
index b9e5240..38ce24d 100644
--- a/core/errors.go
+++ b/core/errors.go
@@ -35,7 +35,7 @@ type FileExistsError struct {
 }
 
 func (err *FileExistsError) Error() string {
-	return "File '" + err.Filename + "' already exists. See the available options on how to proceed."
+	return "file '" + err.Filename + "' already exists - see the available options on how to proceed"
 }
 
 type FormatNotFoundError struct {
@@ -43,7 +43,7 @@ type FormatNotFoundError struct {
 }
 
 func (err *FormatNotFoundError) Error() string {
-	return "Format " + err.FormatName + " is not available."
+	return "format " + err.FormatName + " is not available"
 }
 
 type ChapterNotFoundError struct {
@@ -51,5 +51,27 @@ type ChapterNotFoundError struct {
 }
 
 func (err *ChapterNotFoundError) Error() string {
-	return fmt.Sprintf("Chapter %v not found.", err.ChapterNum)
+	return fmt.Sprintf("chapter %v not found", err.ChapterNum)
+}
+
+type VideoCategoryUnsupportedError struct {
+	Category string
+}
+
+func (err *VideoCategoryUnsupportedError) Error() string {
+	return fmt.Sprintf("video category '%v' not supported", err.Category)
+}
+
+type GtvVideoUrlParseError struct {
+	Url string
+}
+
+func (err *GtvVideoUrlParseError) Error() string {
+	return fmt.Sprintf("Could not parse URL %v", err.Url)
+}
+
+type DownloadInfoFileReadError struct {}
+
+func (err *DownloadInfoFileReadError) Error() string {
+	return "could not read download info file, can't continue download"
 }
diff --git a/core/gtv_api.go b/core/gtv_api.go
index 471a561..f41a9ac 100644
--- a/core/gtv_api.go
+++ b/core/gtv_api.go
@@ -4,7 +4,6 @@ package core
 
 import (
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"iter"
@@ -113,7 +112,7 @@ func GetStreamChunkList(video VideoFormat) (ChunkList, error) {
 	return chunklist, err
 }
 
-func DownloadEpisode(
+func DownloadStreamEpisode(
 	ep StreamEpisode,
 	chapter Chapter,
 	formatName string,
@@ -128,7 +127,7 @@ func DownloadEpisode(
 	return func (yield func(DownloadProgress) bool) {
 		// Set automatic values
 		if outputFile == "" {
-			outputFile = ep.GetProposedFilename(chapter.Index)
+			outputFile = ep.GetProposedFilename(chapter)
 		}
 		if chapter.Index >= 0 {
 			if startDuration < 0 {
@@ -167,7 +166,7 @@ func DownloadEpisode(
 		if continueDl {
 			infoFileData, err := os.ReadFile(infoFilename)
 			if err != nil {
-				yield(DownloadProgress{Error: errors.New("could not access download info file, can't continue download")})
+				yield(DownloadProgress{Error: &DownloadInfoFileReadError{}})
 				return
 			}
 			i, err := strconv.ParseInt(string(infoFileData), 10, 32)
diff --git a/core/gtv_common.go b/core/gtv_common.go
index 9ee0b5a..436e7d5 100644
--- a/core/gtv_common.go
+++ b/core/gtv_common.go
@@ -3,7 +3,6 @@
 package core
 
 import (
-	"errors"
 	"fmt"
 	"regexp"
 	"time"
@@ -40,10 +39,13 @@ func ParseGtvVideoUrl(url string) (GtvVideo, error) {
 	video := GtvVideo{}
 	match := videoUrlRegex.FindStringSubmatch(url)
 	if len(match) < 2 {
-		return video, errors.New("Could not parse URL " + url)
+		return video, &GtvVideoUrlParseError{Url: url}
 	}
 	video.Category = match[1]
 	video.Id = match[2]
+	if video.Category != "streams" {
+		return video, &VideoCategoryUnsupportedError{Category: video.Category}
+	}
 	return video, nil
 }
 
@@ -109,9 +111,21 @@ func (ep *StreamEpisode) GetFormatByName(formatName string) (VideoFormat, error)
 	}
 }
 
-func (ep *StreamEpisode) GetProposedFilename(chapterIdx int) string {
-	if chapterIdx >= 0 && chapterIdx < len(ep.Chapters) {
-		return fmt.Sprintf("GTV%04s - %v. %s.ts", ep.Episode, chapterIdx+1, sanitizeUnicodeFilename(ep.Chapters[chapterIdx].Title))
+func (ep *StreamEpisode) GetChapterByNumber(number int) (Chapter, error) {
+	chapter := Chapter{Index: -1} // set Index to -1 for noop
+	idx := number-1
+	if idx >= 0 && idx >= len(ep.Chapters) {
+		return chapter, &ChapterNotFoundError{ChapterNum: number}
+	}
+	if len(ep.Chapters) > 0 && idx >= 0 {
+		chapter = ep.Chapters[idx]
+	}
+	return chapter, nil
+}
+
+func (ep *StreamEpisode) GetProposedFilename(chapter Chapter) string {
+	if chapter.Index >= 0 && chapter.Index < len(ep.Chapters) {
+		return fmt.Sprintf("GTV%04s - %v. %s.ts", ep.Episode, chapter.Index, sanitizeUnicodeFilename(ep.Chapters[chapter.Index].Title))
 	} else {
 		return sanitizeUnicodeFilename(ep.Title) + ".ts"
 	}