Having issues with AC-3 Passthrough

[KyleMadrid]

Hi all,

I have encoded a few files recently that had AC-3 audio, and I used AC-3 passthrough because I don't want to lose any quality in the audio. But I noticed that when I play the encoded file, the audio is quite a bit lower than the audio in the original. It's not a HUGE difference, but there is definitely a difference.

So I'm just a bit confused because I thought the whole point of using passthrough for audio was so that there is absolutely no quality loss. I was okay with it at first and thought I could just live with it, but then I decided that I wanted to delay the audio in one of the files, so I tried using MKV merge (never had any problems with this program before) and when the file had finished muxing, the audio wouldn't play. There was absolutely no sound at all. I checked with MediaInfo to see if the audio track was there, and it was.

It's very weird because I then tried doing the same thing (delaying audio with mkvmerge) with the original file and it worked without any issues. So it only seems to be an issue with AC-3 passthrough resultant files.

Does anyone have any idea what's happening? Am I doing something wrong?

And before anyone asks, yes, I am DEFINITELY using the AC-3 passthrough option, I'm not accidentally choosing a different option.

I use VidCoder if anyone is wondering.

Thanks in advance to anyone willing to help

[poisondeathray]

What container was the source in ? Sometimes the decoding pathway used will different for different containers (might be using different splitter, decoder, post processing)

What player , software or hardware, did you use to check ?

Use mediainfo (view=>text) post the information for the source file, and encoded file

[KyleMadrid]

Source File

Format : MPEG-TS
File size : 7.38 GiB
Duration : 1h 3mn
Overall bit rate mode : Variable
Overall bit rate : 16.6 Mbps

Video
ID : 514 (0x202)
Menu ID : 3802 (0xEDA)
Format : AVC
Format/Info : Advanced Video Codec
Format profile : Main@L4.0
Format settings, CABAC : Yes
Format settings, ReFrames : 4 frames
Format settings, GOP : M=4, N=12
Codec ID : 27
Duration : 1h 3mn
Bit rate : 15.2 Mbps
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate : 25.000 fps
Standard : PAL
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Interlaced
Scan order : Top Field First
Bits/(Pixel*Frame) : 0.293
Stream size : 6.76 GiB (92%)
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709

Audio #1
ID : 642 (0x282)
Menu ID : 3802 (0xEDA)
Format : MPEG Audio
Format version : Version 1
Format profile : Layer 2
Codec ID : 4
Duration : 1h 3mn
Bit rate mode : Constant
Bit rate : 192 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Compression mode : Lossy
Delay relative to video : 11ms
Stream size : 87.5 MiB (1%)
Language : std
Language, more info : Clean effects

Audio #2
ID : 662 (0x296)
Menu ID : 3802 (0xEDA)
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Format settings, Endianness : Big
Codec ID : 6
Duration : 1h 3mn
Bit rate mode : Constant
Bit rate : 384 Kbps
Channel(s) : 6 channels
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48.0 KHz
Bit depth : 16 bits
Compression mode : Lossy
Delay relative to video : 77ms
Stream size : 175 MiB (2%)
Language : English
Language, more info : Clean effects


Encoded File

Format : Matroska
Format version : Version 2
File size : 2.88 GiB
Duration : 1h 4mn
Overall bit rate : 6 391 Kbps
Writing application : HandBrake 5358svn
Writing library : libmkv 0.6.5

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.1
Format settings, CABAC : Yes
Format settings, ReFrames : 4 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 1h 4mn
Bit rate : 6 000 Kbps
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 50.000 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.130
Stream size : 2.65 GiB (92%)
Writing library : x264 core 130
Encoding settings : cabac=1 / ref=1 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=2 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=0 / me_range=16 / chroma_me=1 / trellis=0 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=0 / threads=6 / lookahead_threads=2 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=1 / keyint=500 / keyint_min=50 / scenecut=40 / intra_refresh=0 / rc_lookahead=10 / rc=abr / mbtree=1 / bitrate=6000 / ratetol=1.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / vbv_maxrate=62500 / vbv_bufsize=78125 / nal_hrd=none / ip_ratio=1.40 / aq=1:1.00
Language : English
Default : Yes
Forced : No
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709

Audio
ID : 2
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Format settings, Endianness : Big
Codec ID : A_AC3
Duration : 1h 4mn
Bit rate mode : Constant
Bit rate : 384 Kbps
Channel(s) : 6 channels
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48.0 KHz
Bit depth : 16 bits
Compression mode : Lossy
Stream size : 177 MiB (6%)
Language : English
Default : Yes
Forced : No



"What player , software or hardware, did you use to check?"

VLC and MPC

[poisondeathray]

mediainfo might not be 100% accurate, but why has the audio length and filesize changed if it's not re-encoded ?

1h 3min vs. 1h 4min
175 Mib vs. 177Mib

If vidcoder has a log file, check it

Please answer the other questions on what software player or hardware used to check this

[KyleMadrid]

Oh, sorry about that, there are 2 source files (both the same type) and 2 encoded files (both the same type) and I accidentally posted the MediaInfo for the second asource file and the MediaInfo for the first encoded file. Does that make sense?

EDIT: Okay, let me rephrase that.

I posted the MediaInfo for source file #2, and the MediaInfo for encoded file #1 (encoded from source file #1)

[KyleMadrid]

Sorry, I answered the question after editing the other post. But anyway, I used VLC and MPC-HC