diff --git a/src/apps/cam/camera_session.cpp b/src/apps/cam/camera_session.cpp
index 097dc479241a..227df9e922ea 100644
--- a/src/apps/cam/camera_session.cpp
+++ b/src/apps/cam/camera_session.cpp
@@ -230,11 +230,16 @@ int CameraSession::start()
 #endif
 
 	if (options_.isSet(OptFile)) {
-		if (!options_[OptFile].toString().empty())
-			sink_ = std::make_unique<FileSink>(camera_.get(), streamNames_,
-							   options_[OptFile]);
-		else
-			sink_ = std::make_unique<FileSink>(camera_.get(), streamNames_);
+		std::unique_ptr<FileSink> sink =
+			std::make_unique<FileSink>(camera_.get(), streamNames_);
+
+		if (!options_[OptFile].toString().empty()) {
+			ret = sink->setFilePattern(options_[OptFile]);
+			if (ret)
+				return ret;
+		}
+
+		sink_ = std::move(sink);
 	}
 
 	if (sink_) {
diff --git a/src/apps/cam/file_sink.cpp b/src/apps/cam/file_sink.cpp
index 3e000d2fd9c6..76e21db9bf9a 100644
--- a/src/apps/cam/file_sink.cpp
+++ b/src/apps/cam/file_sink.cpp
@@ -5,6 +5,7 @@
  * File Sink
  */
 
+#include <array>
 #include <assert.h>
 #include <fcntl.h>
 #include <iomanip>
@@ -12,6 +13,7 @@
 #include <sstream>
 #include <string.h>
 #include <unistd.h>
+#include <utility>
 
 #include <libcamera/camera.h>
 
@@ -24,13 +26,13 @@
 using namespace libcamera;
 
 FileSink::FileSink([[maybe_unused]] const libcamera::Camera *camera,
-		   const std::map<const libcamera::Stream *, std::string> &streamNames,
-		   const std::string &pattern)
+		   const std::map<const libcamera::Stream *, std::string> &streamNames)
 	:
 #ifdef HAVE_TIFF
 	  camera_(camera),
 #endif
-	  streamNames_(streamNames), pattern_(pattern)
+	  pattern_(kDefaultFilePattern), fileType_(FileType::Binary),
+	  streamNames_(streamNames)
 {
 }
 
@@ -38,6 +40,41 @@ FileSink::~FileSink()
 {
 }
 
+int FileSink::setFilePattern(const std::string &pattern)
+{
+	static const std::array<std::pair<std::string, FileType>, 2> types{{
+		{ ".dng", FileType::Dng },
+		{ ".ppm", FileType::Ppm },
+	}};
+
+	pattern_ = pattern;
+
+	if (pattern_.empty() || pattern_.back() == '/')
+		pattern_ += kDefaultFilePattern;
+
+	fileType_ = FileType::Binary;
+
+	for (const auto &type : types) {
+		if (pattern_.size() < type.first.size())
+			continue;
+
+		if (pattern_.find(type.first, pattern_.size() - type.first.size()) !=
+		    std::string::npos) {
+			fileType_ = type.second;
+			break;
+		}
+	}
+
+#ifndef HAVE_TIFF
+	if (fileType_ == FileType::Dng) {
+		std::cerr << "DNG support not available" << std::endl;
+		return -EINVAL;
+	}
+#endif /* HAVE_TIFF */
+
+	return 0;
+}
+
 int FileSink::configure(const libcamera::CameraConfiguration &config)
 {
 	int ret = FrameSink::configure(config);
@@ -67,21 +104,10 @@ bool FileSink::processRequest(Request *request)
 void FileSink::writeBuffer(const Stream *stream, FrameBuffer *buffer,
 			   [[maybe_unused]] const ControlList &metadata)
 {
-	std::string filename;
+	std::string filename = pattern_;
 	size_t pos;
 	int fd, ret = 0;
 
-	if (!pattern_.empty())
-		filename = pattern_;
-
-#ifdef HAVE_TIFF
-	bool dng = filename.find(".dng", filename.size() - 4) != std::string::npos;
-#endif /* HAVE_TIFF */
-	bool ppm = filename.find(".ppm", filename.size() - 4) != std::string::npos;
-
-	if (filename.empty() || filename.back() == '/')
-		filename += "frame-#.bin";
-
 	pos = filename.find_first_of('#');
 	if (pos != std::string::npos) {
 		std::stringstream ss;
@@ -93,7 +119,7 @@ void FileSink::writeBuffer(const Stream *stream, FrameBuffer *buffer,
 	Image *image = mappedBuffers_[buffer].get();
 
 #ifdef HAVE_TIFF
-	if (dng) {
+	if (fileType_ == FileType::Dng) {
 		ret = DNGWriter::write(filename.c_str(), camera_,
 				       stream->configuration(), metadata,
 				       buffer, image->data(0).data());
@@ -104,7 +130,7 @@ void FileSink::writeBuffer(const Stream *stream, FrameBuffer *buffer,
 		return;
 	}
 #endif /* HAVE_TIFF */
-	if (ppm) {
+	if (fileType_ == FileType::Ppm) {
 		ret = PPMWriter::write(filename.c_str(), stream->configuration(),
 				       image->data(0));
 		if (ret < 0)
diff --git a/src/apps/cam/file_sink.h b/src/apps/cam/file_sink.h
index 9d560783af09..71b7fe0feab5 100644
--- a/src/apps/cam/file_sink.h
+++ b/src/apps/cam/file_sink.h
@@ -21,10 +21,11 @@ class FileSink : public FrameSink
 {
 public:
 	FileSink(const libcamera::Camera *camera,
-		 const std::map<const libcamera::Stream *, std::string> &streamNames,
-		 const std::string &pattern = "");
+		 const std::map<const libcamera::Stream *, std::string> &streamNames);
 	~FileSink();
 
+	int setFilePattern(const std::string &pattern);
+
 	int configure(const libcamera::CameraConfiguration &config) override;
 
 	void mapBuffer(libcamera::FrameBuffer *buffer) override;
@@ -32,6 +33,14 @@ public:
 	bool processRequest(libcamera::Request *request) override;
 
 private:
+	static constexpr const char *kDefaultFilePattern = "frame-#.bin";
+
+	enum class FileType {
+		Binary,
+		Dng,
+		Ppm,
+	};
+
 	void writeBuffer(const libcamera::Stream *stream,
 			 libcamera::FrameBuffer *buffer,
 			 const libcamera::ControlList &metadata);
@@ -39,7 +48,10 @@ private:
 #ifdef HAVE_TIFF
 	const libcamera::Camera *camera_;
 #endif
-	std::map<const libcamera::Stream *, std::string> streamNames_;
+
 	std::string pattern_;
+	FileType fileType_;
+
+	std::map<const libcamera::Stream *, std::string> streamNames_;
 	std::map<libcamera::FrameBuffer *, std::unique_ptr<Image>> mappedBuffers_;
 };