player: handle chapter range like --start/--end

Instead of comparing the current chapter every time, set the playback
end timestamp to the chapter end. Likewise, don't execute an extra seek
for the start chapter.

Maybe we could also use the timeline facility to restrict playback to
the given chapter range, but this would be strange when using
--chapter=N to start playback at a given chapter. Then you couldn't seek
back, which is possibly not what the user wants.

player/loadfile.c

@@ -1335,17 +1335,17 @@ goto_reopen_demuxer: ;
     if (startpos == -1 && mpctx->resolve_result &&
         mpctx->resolve_result->start_time > 0)
         startpos = mpctx->resolve_result->start_time;
+    if (startpos == -1 && opts->chapterrange[0] > 0) {
+        double start = chapter_start_time(mpctx, opts->chapterrange[0] - 1);
+        if (start != MP_NOPTS_VALUE)
+            startpos = start;
+    }
     if (startpos == -1 && mpctx->timeline)
         startpos = 0;
     if (startpos != -1) {
         queue_seek(mpctx, MPSEEK_ABSOLUTE, startpos, 0, true);
         execute_queued_seek(mpctx);
     }
-    if (opts->chapterrange[0] > 0) {
-        if (mp_seek_chapter(mpctx, opts->chapterrange[0] - 1))
-            execute_queued_seek(mpctx);
-    }
-
     get_relative_time(mpctx); // reset current delta
 
     if (mpctx->opts->pause)

player/playloop.c

@@ -947,9 +947,9 @@ void run_playloop(struct MPContext *mpctx)
     }
 
     if (opts->chapterrange[1] > 0) {
-        int cur_chapter = get_current_chapter(mpctx);
-        if (cur_chapter != -1 && cur_chapter + 1 > opts->chapterrange[1])
-            mpctx->stop_play = PT_NEXT_ENTRY;
+        double end = chapter_start_time(mpctx, opts->chapterrange[1]);
+        if (end != MP_NOPTS_VALUE && (endpts == MP_NOPTS_VALUE || end < endpts))
+            endpts = end;
     }
 
     if (mpctx->d_audio && !mpctx->restart_playback && !ao_untimed(mpctx->ao)) {