videoio: update ffmpeg backend

- fix compilation for old libraries
- update codec/tag selection logic
- add documentation note about MP4 container tags

modules/videoio/include/opencv2/videoio.hpp

@@ -564,7 +564,9 @@ public:
     @param fourcc 4-character code of codec used to compress the frames. For example,
     VideoWriter::fourcc('P','I','M','1') is a MPEG-1 codec, VideoWriter::fourcc('M','J','P','G') is a
     motion-jpeg codec etc. List of codes can be obtained at [Video Codecs by
-    FOURCC](http://www.fourcc.org/codecs.php) page.
+    FOURCC](http://www.fourcc.org/codecs.php) page. FFMPEG backend with MP4 container natively uses
+    other values as fourcc code: see [ObjectType](http://www.mp4ra.org/codecs.html),
+    so you may receive a warning message from OpenCV about fourcc code conversion.
     @param fps Framerate of the created video stream.
     @param frameSize Size of the video frames.
     @param isColor If it is not zero, the encoder will expect and encode color frames, otherwise it

modules/videoio/src/cap_ffmpeg_impl.hpp

@@ -1543,7 +1543,7 @@ void CvVideoWriter_FFMPEG::close()
 #define CV_PRINTABLE_CHAR(ch) ((ch) < 32 ? '?' : (ch))
 #define CV_TAG_TO_PRINTABLE_CHAR4(tag) CV_PRINTABLE_CHAR((tag) & 255), CV_PRINTABLE_CHAR(((tag) >> 8) & 255), CV_PRINTABLE_CHAR(((tag) >> 16) & 255), CV_PRINTABLE_CHAR(((tag) >> 24) & 255)
 
-static inline bool cv_ff_codec_tag_match(const AVCodecTag *tags, enum AVCodecID id, unsigned int tag)
+static inline bool cv_ff_codec_tag_match(const AVCodecTag *tags, CV_CODEC_ID id, unsigned int tag)
 {
     while (tags->id != AV_CODEC_ID_NONE)
     {
@@ -1553,7 +1553,7 @@ static inline bool cv_ff_codec_tag_match(const AVCodecTag *tags, enum AVCodecID
     }
     return false;
 }
-static inline bool cv_ff_codec_tag_list_match(const AVCodecTag *const *tags, enum AVCodecID id, unsigned int tag)
+static inline bool cv_ff_codec_tag_list_match(const AVCodecTag *const *tags, CV_CODEC_ID id, unsigned int tag)
 {
     int i;
     for (i = 0; tags && tags[i]; i++) {
@@ -1611,21 +1611,24 @@ bool CvVideoWriter_FFMPEG::open( const char * filename, int fourcc,
 #if LIBAVCODEC_VERSION_INT<((51<<16)+(49<<8)+0)
     if( (codec_id = codec_get_bmp_id( fourcc )) == CV_CODEC(CODEC_ID_NONE) )
         return false;
-#elif LIBAVFORMAT_BUILD >= CALC_FFMPEG_VERSION(54, 1, 0)
-// APIchnages:
-// 2012-01-31 - dd6d3b0 - lavf 54.01.0
-//   Add avformat_get_riff_video_tags() and avformat_get_riff_audio_tags().
+#else
     if( (codec_id = av_codec_get_id(fmt->codec_tag, fourcc)) == CV_CODEC(CODEC_ID_NONE) )
     {
         const struct AVCodecTag * fallback_tags[] = {
+#if LIBAVFORMAT_BUILD >= CALC_FFMPEG_VERSION(54, 1, 0)
+// APIchanges:
+// 2012-01-31 - dd6d3b0 - lavf 54.01.0
+//   Add avformat_get_riff_video_tags() and avformat_get_riff_audio_tags().
                 avformat_get_riff_video_tags(),
-#if LIBAVFORMAT_BUILD >= CALC_FFMPEG_VERSION(55, 25, 100)
+#endif
+#if LIBAVFORMAT_BUILD >= CALC_FFMPEG_VERSION(55, 25, 100) && defined LIBAVFORMAT_VERSION_MICRO && LIBAVFORMAT_VERSION_MICRO >= 100
 // APIchanges: ffmpeg only
 // 2014-01-19 - 1a193c4 - lavf 55.25.100 - avformat.h
 //   Add avformat_get_mov_video_tags() and avformat_get_mov_audio_tags().
-                // TODO ffmpeg only, need to skip libav: avformat_get_mov_video_tags(),
+                avformat_get_mov_video_tags(),
 #endif
-                codec_bmp_tags, NULL };
+                codec_bmp_tags, // fallback for avformat < 54.1
+                NULL };
         if( (codec_id = av_codec_get_id(fallback_tags, fourcc)) == CV_CODEC(CODEC_ID_NONE) )
         {
             fflush(stdout);
@@ -1650,10 +1653,6 @@ bool CvVideoWriter_FFMPEG::open( const char * filename, int fourcc,
             fourcc = supported_tag;
         }
     }
-#else
-    const struct AVCodecTag * tags[] = { codec_bmp_tags, NULL};
-    if( (codec_id = av_codec_get_id(tags, fourcc)) == CV_CODEC(CODEC_ID_NONE) )
-        return false;
 #endif
 
     // alloc memory for context