From 4b05765174fa2a0750aa8acc252329d6df73c2f1 Mon Sep 17 00:00:00 2001
From: cudawarped <12133430+cudawarped@users.noreply.github.com>
Date: Tue, 2 Aug 2022 17:18:42 +0300
Subject: [PATCH] Initial fix to try and return a valid fourcc when
 _opencv_avcodec_get_name fails.

---
 modules/videoio/src/cap_ffmpeg_impl.hpp | 20 +++++++++++++++++---
 modules/videoio/test/test_ffmpeg.cpp    | 25 +++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/modules/videoio/src/cap_ffmpeg_impl.hpp b/modules/videoio/src/cap_ffmpeg_impl.hpp
index d02b045..caeae31 100644
--- a/modules/videoio/src/cap_ffmpeg_impl.hpp
+++ b/modules/videoio/src/cap_ffmpeg_impl.hpp
@@ -1699,7 +1699,7 @@ double CvCapture_FFMPEG::getProperty( int property_id ) const
         return (double)av_get_picture_type_char(picture->pict_type);
     case CAP_PROP_FPS:
         return get_fps();
-    case CAP_PROP_FOURCC:
+    case CAP_PROP_FOURCC: {
         codec_id = video_st->CV_FFMPEG_CODEC_FIELD->codec_id;
         codec_tag = (double) video_st->CV_FFMPEG_CODEC_FIELD->codec_tag;
 
@@ -1709,12 +1709,26 @@ double CvCapture_FFMPEG::getProperty( int property_id ) const
         }
 
         codec_fourcc = _opencv_avcodec_get_name(codec_id);
-        if(!codec_fourcc || strlen(codec_fourcc) < 4 || strcmp(codec_fourcc, "unknown_codec") == 0)
+        if (!codec_fourcc || strcmp(codec_fourcc, "unknown_codec") == 0 || strlen(codec_fourcc) != 4)
         {
-            return codec_tag;
+            const struct AVCodecTag* fallback_tags[] = {
+            // 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) && 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().
+                avformat_get_mov_video_tags(),
+#endif
+                codec_bmp_tags, // fallback for avformat < 54.1
+                NULL };
+            return av_codec_get_tag(fallback_tags, codec_id);
         }
 
         return (double) CV_FOURCC(codec_fourcc[0], codec_fourcc[1], codec_fourcc[2], codec_fourcc[3]);
+    }
     case CAP_PROP_SAR_NUM:
         return _opencv_ffmpeg_get_sample_aspect_ratio(ic->streams[video_stream]).num;
     case CAP_PROP_SAR_DEN:
diff --git a/modules/videoio/test/test_ffmpeg.cpp b/modules/videoio/test/test_ffmpeg.cpp
index 1157057..f59631c 100644
--- a/modules/videoio/test/test_ffmpeg.cpp
+++ b/modules/videoio/test/test_ffmpeg.cpp
@@ -399,7 +399,32 @@ const ffmpeg_cap_properties_param_t videoio_ffmpeg_properties[] = {
 
 INSTANTIATE_TEST_CASE_P(videoio, ffmpeg_cap_properties, testing::ValuesIn(videoio_ffmpeg_properties));
 
+typedef tuple<string, string> ffmpeg_get_fourcc_param_t;
+typedef testing::TestWithParam<ffmpeg_get_fourcc_param_t> ffmpeg_get_fourcc;
 
+TEST_P(ffmpeg_get_fourcc, check_short_codecs)
+{
+    const VideoCaptureAPIs api = CAP_FFMPEG;
+    if (!videoio_registry::hasBackend(api))
+        throw SkipTestException("Backend was not found");
+    const string fileName = get<0>(GetParam());
+    const string fourcc = get<1>(GetParam());
+    VideoCapture cap(findDataFile(fileName), api);
+    if (!cap.isOpened())
+        throw SkipTestException("Video stream is not supported");
+    ASSERT_EQ(fourccToString(cap.get(CAP_PROP_FOURCC)), fourcc);
+}
+
+const ffmpeg_get_fourcc_param_t ffmpeg_get_fourcc_param[] =
+{
+    ffmpeg_get_fourcc_param_t("../cv/tracking/faceocc2/data/faceocc2.webm", "VP80"),
+    ffmpeg_get_fourcc_param_t("video/sample_322x242_15frames.yuv420p.libvpx-vp9.mp4", "vp09"),
+    ffmpeg_get_fourcc_param_t("video/sample_322x242_15frames.yuv420p.libaom-av1.mp4", "av01"),
+    ffmpeg_get_fourcc_param_t("video/big_buck_bunny.h265", "hevc"),
+    ffmpeg_get_fourcc_param_t("video/big_buck_bunny.h264", "h264")
+};
+
+INSTANTIATE_TEST_CASE_P(videoio, ffmpeg_get_fourcc, testing::ValuesIn(ffmpeg_get_fourcc_param));
 
 // related issue: https://github.com/opencv/opencv/issues/15499
 TEST(videoio, mp4_orientation_meta_auto)
-- 
2.7.4