Merge pull request opencv#19667 from alalek:hotfix_ffmpeg_hw_accel

Author: alalek

modules/videoio/src/cap_ffmpeg_hw.hpp

@@ -486,7 +486,7 @@ class HWAccelIterator {
         if (va_type == VIDEO_ACCELERATION_ANY)
         {
             if (!accel_list.empty())
-                accel_list = ",";  // add no-acceleration case to the end of the list
+                accel_list += ",";  // add no-acceleration case to the end of the list
         }
         CV_LOG_DEBUG(NULL, "FFMPEG: allowed acceleration types (" << getVideoAccelerationName(va_type) << "): '" << accel_list << "'");
 

modules/videoio/src/cap_ffmpeg_impl.hpp

@@ -572,7 +572,7 @@ void CvCapture_FFMPEG::init()
     memset(&packet_filtered, 0, sizeof(packet_filtered));
     av_init_packet(&packet_filtered);
     bsfc = NULL;
-    va_type = cv::VIDEO_ACCELERATION_ANY;
+    va_type = cv::VIDEO_ACCELERATION_NONE;  // TODO OpenCV 5.0: change to _ANY?
     hw_device = -1;
 }