Very bizarre audio issue

[Boxcart]

Hi all,

Recently I've encountered an extremely confusing issue that I need help with. I'll try to be as concise as I can.

I record content with a Blackmagic Media DeckLink card using ffmpeg. I mostly capture old movies that I have to put on my Plex server. I typically use the EAC3 (Dolby Digital Plus) encoder with ffmpeg as I've found it most faithfully/identically captures the original audio quality and sounds better than the other encoders that ffmpeg has which I have tested. AC3 (Dolby Digital) also sounds very good but EAC3 has a higher bit rate so I go with that. This process produces lossless/reference quality recordings that look and sound perfect, with one issue being this sound issue in my Home Theater room that does not occur on other devices/setups with the same files.

I've noticed that when I add these output movies to my Plex server, and play them back through Plex on an NVIDIA Shield connected to my Yamaha AVR (which is connected to my home theater speakers) Dolby Digital Plus (EAC3) and only that format comes through as garbled screeching. Every other audio format (Dolby Atmos, DTS, Dolby Digital, etc.) plays just fine.

The DD+ audio will play just fine on my PC (although it's not truly a DD+ setup it's just playing through my speakers or headphones) as well as through Plex on my iPhone and other devices. Therefore I figured there was a problem with my NVIDIA Shield. So then I connected other devices to the Yamaha AVR and played the same content and got the same problem, so I ruled out the NVIDIA Shield. Then I figured it was my AVR maybe having a bad board and being unable to decode DD+ but not other formats for some reason. I got the idea to download reference Dolby Digital Plus files from Dolby and try those (in other words not my ffmpeg creations) and what do you know, they played just fine.

On my NVIDIA Shield, if I turn on Dolby processing (which processes the audio on the device instead of sending it to the AVR to decode and sends lower quality processed audio to the AVR) or if I turn off DD+ (which sends the audio to the AVR instead as PCM which doesn't sound as good) the sounds comes through properly without the garbled/corrupted sound.

For some reason though, there is something about the Dolby Digital Plus/EAC3 that I am creating with ffmpeg that a real AVR cannot process for some reason. Dolby Digital Plus from other sources works just fine.

Here is the ffmpeg command I am using:

ffmpeg -f dshow -c:v v210 -video_pin_name 1 -audio_pin_name 1 -video_size 1920x1080 -rtbufsize 2147480000 -framerate 24000/1001 -channels 6 -sample_rate 48k -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 bt709 -color_primaries bt709 -colorspace bt709 -strict -2 -c:a eac3 -b:a 6144k -c:v hevc_nvenc -profile:v main10 -preset:v p7 -b:v 80M -bufsize:v 120M -maxrate 90M -minrate 70M -g 4 -t 02:40:00 MovieName.mkv

Here is the MediaInfo reading of one of the affected files:

Format                                   : Matroska
Format version                           : Version 4
File size                                : 23.5 GiB
Duration                                 : 1 h 59 min
Overall bit rate                         : 28.0 Mb/s
Encoded date                             : UTC 2023-12-01 17:31:57
Writing application                      : mkvmerge v67.0.0 ('Under Stars') 64-bit
Writing library                          : libebml v1.4.2 + libmatroska v1.6.4 / Lavf60.3.100

Video
ID                                       : 1
Format                                   : HEVC
Format/Info                              : High Efficiency Video Coding
Format profile                           : Main 10@L5.1@High
Codec ID                                 : V_MPEGH/ISO/HEVC
Duration                                 : 1 h 59 min
Bit rate                                 : 21.9 Mb/s
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 23.976 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 10 bits
Bits/(Pixel*Frame)                       : 0.110
Stream size                              : 18.3 GiB (78%)
Writing library                          : Lavc60.3.100 hevc_nvenc
Language                                 : English
Default                                  : No
Forced                                   : No
Color range                              : Limited
Color primaries                          : BT.2020
Transfer characteristics                 : PQ
Matrix coefficients                      : BT.2020 non-constant

Audio
ID                                       : 2
Format                                   : E-AC-3
Format/Info                              : Enhanced AC-3
Commercial name                          : Dolby Digital Plus
Codec ID                                 : A_EAC3
Duration                                 : 1 h 59 min
Bit rate mode                            : Constant
Bit rate                                 : 6 144 kb/s
Channel(s)                               : 6 channels
Channel layout                           : L R C LFE Ls Rs
Sampling rate                            : 48.0 kHz
Frame rate                               : 187.500 FPS (256 SPF)
Bit depth                                : 32 bits
Compression mode                         : Lossy
Delay relative to video                  : 9 ms
Stream size                              : 5.15 GiB (22%)
Writing library                          : Lavc60.3.100 eac3
Language                                 : English
Service kind                             : Complete Main
Default                                  : No
Forced                                   : No

If anyone could help me figure this out I would very much appreciate it. I've exhausted all options in terms of the player since it happened on multiple devices, and the receiver, since other EAC3 sources besides my ffmpeg recordings work fine, so I would believe there's something wrong in here. I will note turning off the AI function on the AVR made the problem go from garbled DD+ audio to basically no audio with some popping, but everything else is the same. Since other DD+ content worked but mine doesn't on the AVR, I'm lead to believe there is something wrong with the audio encoding/capturing.

Thanks!

[davexnet]

Have you seen anything different in the files when looking at them in mediainfo?
Is the problem related to the bitrate?

[Boxcart]

Have you seen anything different in the files when looking at them in mediainfo?
Is the problem related to the bitrate?

Here's the MediaInfo reading on the Dolby Digital Plus file I downloaded from Dolby that doesn't have a sound issue on the NVIDIA Shield (Plex)/Yamaha AVR:

Audio
ID                                       : 1
Format                                   : E-AC-3
Format/Info                              : Enhanced AC-3
Commercial name                          : Dolby Digital Plus
Codec ID                                 : ec-3
Duration                                 : 1 min 11 s
Bit rate mode                            : Constant
Bit rate                                 : 256 kb/s
Channel(s)                               : 6 channels
Channel layout                           : L R C LFE Ls Rs
Sampling rate                            : 48.0 kHz
Frame rate                               : 31.250 FPS (1536 SPF)
Compression mode                         : Lossy
Stream size                              : 2.20 MiB (9%)
Service kind                             : Complete Main
Default                                  : Yes
Alternate group                          : 2
Encoded date                             : UTC 2016-11-11 07:46:21
Tagged date                              : UTC 2016-11-11 07:46:21

And here's the MediaInfo readout on a problem recording:

Audio
ID                                       : 2
Format                                   : E-AC-3
Format/Info                              : Enhanced AC-3
Commercial name                          : Dolby Digital Plus
Codec ID                                 : A_EAC3
Duration                                 : 1 h 59 min
Bit rate mode                            : Constant
Bit rate                                 : 6 144 kb/s
Channel(s)                               : 6 channels
Channel layout                           : L R C LFE Ls Rs
Sampling rate                            : 48.0 kHz
Frame rate                               : 187.500 FPS (256 SPF)
Bit depth                                : 32 bits
Compression mode                         : Lossy
Delay relative to video                  : 9 ms
Stream size                              : 5.15 GiB (22%)
Writing library                          : Lavc60.3.100 eac3
Language                                 : English
Service kind                             : Complete Main
Default                                  : No
Forced                                   : No

[davexnet]

Yes but your problem file shows this and you haven't stated whether any files work at this maxed out bitrate

Bit rate               : 6 144 kb/s

[Boxcart]

Yes but your problem file shows this and you haven't stated whether any files work at his maxed out bitrate

Bit rate               : 6 144 kb/s

Those files work if I let the NVIDIA Shield process the Dolby audio in the settings (but it will have a faint, intermittent clipping/popping sound) or alternatively if I just turn off DD+ (but leave all the other audio formats on in the NVIDIA Shield settings) it will then be sent to the Yamaha AVR as PCM which works without issue, but subjectively does not sound as good/rich as Dolby.

It's also worth pointing out that all of my AC3 (not EAC3) ffmpeg recordings also use maxed out bitrates (640 kbps in the case of AC3) and play without any issue at all. Those recordings are made using the same ffmpeg command from above, but simply changing "eac3" to "ac3." It's just DD+/EAC3 with the problem for some reason.

[davexnet]

Unless you can find a sample file that plays normally at that bitrate it points to something in your playback chain
as being incompatible with it

[Boxcart]

Unless you can find a sample file that plays normally at that bitrate it points to something in your playback chain
as being incompatible with it

Yup the bitrate was the issue. I just ran one of the problem videos through ffmpeg again and the only command I entered was to lower the audio bitrate to half of what it was at before (which was overkill) and leave the rest of the file alone. Now Dolby Digital Plus works perfectly. Thank you!

[davexnet]

Unless you can find a sample file that plays normally at that bitrate it points to something in your playback chain
as being incompatible with it

Yup the bitrate was the issue. I just ran one of the problem videos through ffmpeg again and the only command I entered was to lower the audio bitrate to half of what it was at before (which was overkill) and leave the rest of the file alone. Now Dolby Digital Plus works perfectly. Thank you!

You're welcome.