File video capture device supports MJPEG format

media/capture/video/file_video_capture_device.h

Index: media/capture/video/file_video_capture_device.h
diff --git a/media/capture/video/file_video_capture_device.h b/media/capture/video/file_video_capture_device.h
index f50f04146d37094c6d3033412336858461961233..a026db3cbf3ecca09491bb13f02658a0bb2b70e7 100644
--- a/media/capture/video/file_video_capture_device.h
+++ b/media/capture/video/file_video_capture_device.h
@@ -8,6 +8,7 @@
 #include <string>
 
 #include "base/files/file.h"
+#include "base/files/memory_mapped_file.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_checker.h"
@@ -17,21 +18,31 @@ namespace media {
 
 // Implementation of a VideoCaptureDevice class that reads from a file. Used for
 // testing the video capture pipeline when no real hardware is available. The
-// only supported file format is YUV4MPEG2 (a.k.a. Y4M), a minimal container
-// with a series of uncompressed video only frames, see the link
-// http://wiki.multimedia.cx/index.php?title=YUV4MPEG2 for more information
-// on the file format. Several restrictions and notes apply, see the
+// supported file formats are YUV4MPEG2 (a.k.a. Y4M) and MJPEG/JPEG. YUV4MPEG2
+// is a minimal container with a series of uncompressed video only frames, see
+// the link http://wiki.multimedia.cx/index.php?title=YUV4MPEG2 for more
+// information on the file format. Several restrictions and notes apply, see the
 // implementation file.
-// Example videos can be found in http://media.xiph.org/video/derf.
+// Example Y4M videos can be found in http://media.xiph.org/video/derf.

[mcasas, 2015/08/18 18:28:42]

Any example MJPEG files plz?

[henryhsu, 2015/08/19 01:57:24]

media/data/test/bear.mjpeg concatenates many MJPEG images into a file.
Therefore, MJPEG stream doesn't describe the frame rate.

 class MEDIA_EXPORT FileVideoCaptureDevice : public VideoCaptureDevice {

[mcasas, 2015/08/18 18:28:42]

Hmmm, I have the impression that we are mixing two
different things. 

Proposal: Refactor this into three classes:

FileVideoCaptureDevice holds the generic parts,
and has a |scoped_ptr<VideoFileParser> file_parser_;|
member. 

VideoFileParser is implemented in the .cc file 
as either MjpegFileParser or Y4MFileParser.

FVCD() ctor checks the extension of the file and
creates the appropriate parser, using
base::EndsWith(file_name.c_str(), suffix, base::CompareCase::INSENSITIVE_ASCII)
(bonus points for a VideoFileParser factory method).

All header parsing might be stuffed into a
bool VideoFileParser::Init();

FVCD uses VFP only real method after that:

const uint8_t* VideoFileParser::GetNextFrame();

WDYT?

[henryhsu, 2015/08/19 01:57:24]

SGTM. VideoFileParser still uses MemoryMappedFile. 

  public:
-  static int64 ParseFileAndExtractVideoFormat(
-      base::File* file,
-      media::VideoCaptureFormat* video_format);
-  static base::File OpenFileForRead(const base::FilePath& file_path);
+  // Reads and parses the header of a |mapped_file|, returning the collected
+  // pixel format in |video_format| and storing current frame size in
+  // |frame_size|. Returns the index of the first byte of the first video
+  // frame. If parsing |mapped_file| failed, returns -1.
+  // Restrictions: Only trivial Y4M per-frame headers and MJPEG are supported.
+  static size_t ParseFileAndExtractVideoFormat(
+      const base::MemoryMappedFile* mapped_file,
+      media::VideoCaptureFormat* video_format,
+      int* frame_size);
+
+  // Opens a given file for reading, and returns the memory mapped file to the
+  // caller, who is responsible for closing it.
+  static scoped_ptr<base::MemoryMappedFile>
+      OpenFileForRead(const base::FilePath& file_path);
 
   // Constructor of the class, with a fully qualified file path as input, which
-  // represents the Y4M video file to stream repeatedly.
+  // represents the Y4M or MJPEG file to stream repeatedly.
   explicit FileVideoCaptureDevice(const base::FilePath& file_path);
 
   // VideoCaptureDevice implementation, class methods.
@@ -41,14 +52,11 @@ class MEDIA_EXPORT FileVideoCaptureDevice : public VideoCaptureDevice {
   void StopAndDeAllocate() override;
 
  private:
-  // Returns size in bytes of an I420 frame, not including possible paddings,
-  // defined by |capture_format_|.
-  int CalculateFrameSize() const;
-
   // Called on the |capture_thread_|.
   void OnAllocateAndStart(const VideoCaptureParams& params,
                           scoped_ptr<Client> client);
   void OnStopAndDeAllocate();
+  const uint8_t* GetNextFrame();
   void OnCaptureTask();
 
   // |thread_checker_| is used to check that destructor, AllocateAndStart() and
@@ -61,12 +69,11 @@ class MEDIA_EXPORT FileVideoCaptureDevice : public VideoCaptureDevice {
   // The following members belong to |capture_thread_|.
   scoped_ptr<VideoCaptureDevice::Client> client_;
   const base::FilePath file_path_;
-  base::File file_;
-  scoped_ptr<uint8[]> video_frame_;
+  scoped_ptr<base::MemoryMappedFile> mapped_file_;

[mcasas, 2015/08/18 18:28:42]

A typical Y4M file can be a few Gigabytes long,
would MemoryMappedFile handle it correctly?

[henryhsu, 2015/08/19 01:57:24]

MemoryMapedFile doesn't mention the size limitation.
And I also tested crowd720_25frames.y4m which is used in autotest.
Could you provide a Y4M file then I can test it?

[henryhsu, 2015/08/19 10:05:11]

Y4mFileParser uses original base::File implementation. MjpegFileParser uses
MemoryMappedFile.

   VideoCaptureFormat capture_format_;
   int frame_size_;
-  int64 current_byte_index_;
-  int64 first_frame_byte_index_;
+  size_t current_byte_index_;
+  size_t first_frame_byte_index_;
   // Target time for the next frame.
   base::TimeTicks next_frame_time_;