Hi folks,
I'm hoping someone might be able to help me figure out a strange sound problem that has plagued my setup for a few years now. It's a small intermittent issue I've come to live with, but I'm trying to solve it yet again. I use ffmpeg to record using a Blackmagic decklink capture card in my PC. There is an HDMI input into that. I use a customized recording command (below).

The problem I've had since the beginning of using this setup is recordings, regardless of length, about half the time get this high pitched crackling sound that lasts around 10-60 seconds once in the recording. The product is otherwise flawless. Over time I learned that about 95% of the time, this problem occurs in the first 20 minutes of recording. So the way around it I found is to simply restart the source 20 minutes after the ffmpeg recording command is started, and then lop off that 20 minutes later using MakeMKV.

I'm getting tired of doing that and I want to try to figure what this could possibly be. I tried replacing the Blackmagic card in case it was defective and that didn't solve it; the same thing happened with a new card. I also tried recording using different software besides ffmpeg including Blackmagic's native recording program and the same sound issue happened. At this point I'm stumped. Any ideas are appreciated. Thanks.

My ffmpeg recording command:
Code:
ffmpeg -f dshow -c:v v210 -video_pin_name 1 -audio_pin_name 1 -video_size 3840x2160 -rtbufsize 2147480000 -framerate 24000/1001 -channels 6 -sample_rate 48k -sample_size 16 -i video="Decklink Video Capture":audio="Decklink Audio Capture" -filter_complex "[0:0]scale=w=iw:h=ih:interl=false:eval=init:out_v_chr_pos=-128:out_h_chr_pos=-128:flags=bilinear+accurate_rnd+print_info,format=p010le[vout];[0:1]channelmap=FL-FL|FR-FR|LFE-FC|FC-LFE|BL-BL|BR-BR:5.1[aout]" -map "[vout]" -map "[aout]" -color_range 1 -chroma_sample_location left -color_trc smpte2084 -color_primaries bt2020 -colorspace bt2020nc -strict -2 -c:a eac3 -b:a 3072k -c:v hevc_nvenc -profile:v main10 -preset:v p7 -b:v 80M -bufsize:v 120M -maxrate 90M -minrate 70M -g 4 -t 02:25:00 Recording.mkv
A recording sample of the problem (problem starts at right about 22 seconds in): https://drive.google.com/file/d/1mjK62PpAj0446MBP3rL4FeoL1zhjrH4F/view?usp=sharing

Thanks