Add output format selection to settings

Introduces new settings for forcing output format when merging videos, allowing users to select a preferred format (mp4, webm, mkv). Updates all language files with relevant translations, adds UI controls in the settings dialog, persists settings via ConfigManager, and passes options through the download workflow to yt-dlp.

src/core/ytsage_downloader.py

@@ -58,6 +58,8 @@ class DownloadThread(QThread):
         force_keyframes=False,
         proxy_url=None,
         geo_proxy_url=None,
+        force_output_format=False,
+        preferred_output_format="mp4",
     ) -> None:
         super().__init__()
         self.url = url
@@ -81,6 +83,8 @@ class DownloadThread(QThread):
         self.force_keyframes = force_keyframes
         self.proxy_url = proxy_url
         self.geo_proxy_url = geo_proxy_url
+        self.force_output_format = force_output_format
+        self.preferred_output_format = preferred_output_format
         self.paused = False
         self.cancelled = False
         self.process = None
@@ -189,6 +193,17 @@ class DownloadThread(QThread):
             res_value = self.resolution if self.resolution else "720"  # Default to 720p if no resolution specified
             cmd.extend(["-S", f"res:{res_value}"])
 
+        # Force output format if enabled and merging is needed
+        if self.force_output_format and not self.is_audio_only:
+            if self.format_has_audio:
+                # Progressive format (video with audio) - use remux to convert container
+                cmd.extend(["--remux-video", self.preferred_output_format])
+                logger.debug(f"Using --remux-video to force progressive format to: {self.preferred_output_format}")
+            else:
+                # Merging video+audio - force merge output format
+                cmd.extend(["--merge-output-format", self.preferred_output_format])
+                logger.debug(f"Using --merge-output-format to force merged format to: {self.preferred_output_format}")
+
         # Output template with resolution in filename
         # Use string concatenation instead of Path.joinpath to avoid Path object issues
         base_path = self.path.as_posix()