faster chapter splitting

Since there is an issue with this fix when applied on flac option, the changes dont take effect on flac.
For more information have a look in KrumpetPirate/AAXtoMP3 issue #142.

AAXtoMP3

@@ -542,14 +542,18 @@ do
         chapter_title="${title}-$(printf %0${#chaptercount}d $chapternum) ${chapter}"
         chapter_file="${output_directory}/${chapter_title}.${extension}"
 
-        # the ID3 tags must only be specified for *.mp3 files,
-        # the other container formats come with their own
-        # tagging mechanisms.
-        id3_version_param=""
-        if test "${extension}" = "mp3"; then
-          id3_version_param="-id3v2_version 3"
+        # Since the .aax file allready got converted we can use
+        # -acodec copy, which is much faster than a reencodation.
+        # Since there is an issue when using copy on flac, where
+        # the duration of the chapters gets shown as if they where
+        # as long as the whole audiobook.
+        chapter_codec=""
+        if test "${extension}" = "flac"; then
+          chapter_codec="-acodec flac "${compression_level_param}""
+        else
+          chapter_codec="-acodec copy"
         fi
-
+        
         # Big Long chapter debug
         debug_vars "Chapter Variables:" cover_file chapter_start chapter_end id3_version_param chapternum chapter_title chapter_file
         if [ "$((${continueAt} > ${chapternum}))" = "0" ]; then
@@ -564,8 +568,7 @@ do
             -i "${cover_file}" \
             -map 0:0 \
             -map 1:0 \
-            -acodec "${codec}" ${id3_version_param} \
-            ${compression_level_param} \
+            ${chapter_codec} \
             -metadata:s:v title="Album cover" \
             -metadata:s:v comment="Cover (Front)" \
             -metadata track="${chapternum}" \