Audio format problem with ffmpeg

[Boxcart]

Hi all,

I'm using ffmpeg to capture audio and video with a Blackmagic Design DeckLink card. It's taken some time to get the ffmpeg command right, and for a while I dealt with a random audio crackling problem. Basically a recording of around an hour would have one or two instances of ~10 second segments having crackling audio at random places. The rest would be perfect.

I've been using this ffmpeg command:

ffmpeg -f dshow -c:v v210 -video_pin_name 1 -audio_pin_name 1 -video_size 3840x2160 -rtbufsize 2147480000 -framerate 24000/1000 -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 ac3 -b:a 640k -c:v hevc_nvenc -profile:v main10 -preset:v p7 -b:v 80M -bufsize:v 120M -maxrate 90M -minrate 60M -g 4 -t HH:MM:SS title.mkv

Following up on prior threads dealing with different, disparate issues, I figured out what was causing the random audio crackling problem, and now have a 100% working command that's awesome. I found that to fix the crackling problem, I needed to change

-c:a

from AC3 or EAC3 to pcm_s24le (the signal coming into the DeckLink card is actually PCM) the crackling completely goes away. I left all of the other parameters in the command above exactly the same. However I need your help with one final adjustment if possible. Pcm_s24le results in less "rich" audio. It seems like the volume is lower and it makes less use of the surround speakers. It's still good audio however, but action scenes tend to suffer. Also with pcm_s24le the LFE in loud scenes can sound blown out in the room through the subwoofers.

Can I convert this audio to AC3 with ffmpeg? Would that just recreate the crackling problem or solve this one? Now that it is known that using a PCM format to record the PCM input makes the crackling go away, is there an adjustment that could be made to the command to get the same richness and proper use of channels as when using EAC3 or AC3?

Thanks!