Just tried my normal encoding process on a new .mp4 file. The process is: demuxing the source, encoding the video to MPEG2 with HCENC, audio to AC3 with ffmpeg, then remux with mplex to get a file suitable for DVD authoring. But it didn't work; the audio is about 4 seconds delayed compared to the video. Looking at the source file in more detail with mp4box, it appears that the audio stream is 4 seconds longer than the video. I assume there's a flag somewhere in the multiplexing data of the file that says to skip the first 4 seconds of the audio stream (which are completely silent), but can anyone point me in the direction of something that can read it and confirm that this is what's really going on...?
Try StreamFab Downloader and download from Netflix, Amazon, Youtube! Or Try DVDFab and copy Blu-rays! or rip iTunes movies!
+ Reply to Thread
Results 1 to 9 of 9
Thread
-
-
are the video & audio the same lengths and just shifted 4 seconds apart? this would be constant 4 seconds throughout the whole video
or are they different lengths? this would be progressively worsening A/V sync over time
or is it completely something else?
What are the specs of the mp4 file? use mediainfo (view=>text) copy & paste the info back here
Are you making a PAL spec DVD? -
Format : MPEG-4
Format profile : Base Media
Codec ID : isom
File size : 2.50 GiB
Duration : 2h 10mn
Overall bit rate : 2 743 Kbps
Encoded date : UTC 2010-09-17 01:09:14
Tagged date : UTC 2010-09-17 01:09:14
Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.1
Format settings, CABAC : Yes
Format settings, ReFrames : 4 frames
Format settings, GOP : M=4, N=48
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 2h 10mn
Bit rate mode : Variable
Bit rate : 2 366 Kbps
Maximum bit rate : 15.1 Mbps
Width : 1 280 pixels
Height : 544 pixels
Display aspect ratio : 2.35:1
Frame rate mode : Constant
Frame rate : 23.976 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.142
Stream size : 2.15 GiB (86%)
Writing library : x264 core 104 r1677 19df41a
Encoding settings : cabac=1 / ref=4 / deblock=1:0:0 / analyse=0x3
:0x113 / me=hex / subme=4 / psy=1 / psy_rd=0.00:0.00 / mixed_ref=0 / me_range=16
/ chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 /
chroma_qp_offset=0 / threads=3 / sliced_threads=0 / nr=0 / decimate=1 / interlac
ed=0 / constrained_intra=0 / bframes=3 / b_pyramid=0 / b_adapt=1 / b_bias=0 / di
rect=1 / weightb=1 / open_gop=0 / weightp=1 / keyint=250 / keyint_min=23 / scene
cut=40 / intra_refresh=0 / rc_lookahead=40 / rc=2pass / mbtree=1 / bitrate=2366
/ ratetol=1.0 / qcomp=0.60 / qpmin=10 / qpmax=51 / qpstep=4 / cplxblur=20.0 / qb
lur=0.5 / ip_ratio=1.40 / aq=1:1.00
Encoded date : UTC 2010-09-16 14:12:54
Tagged date : UTC 2010-09-17 01:12:55
Audio
ID : 2
Format : AAC
Format/Info : Advanced Audio Codec
Format profile : LC
Codec ID : 40
Duration : 2h 10mn
Bit rate mode : Variable
Bit rate : 375 Kbps
Maximum bit rate : 496 Kbps
Channel(s) : 6 channels
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48.0 KHz
Compression mode : Lossy
Stream size : 350 MiB (14%)
Language : English
Encoded date : UTC 2010-09-17 01:12:18
Tagged date : UTC 2010-09-17 01:12:55
The offset is a constant 4 seconds. It's as if on playback the first 4 seconds of the source file's audio should be ignored. Yes, I'm making a PAL dvd, although the same problem occurs if I go for NTSC-film.
Edit: The duration accuracy mediainfo produces in its default format isn't enough to see the problem. Here's the full accuracy version:
Video Duration : 02:10:25.284
Audio Duration : 02:10:29.930 -
If it's a constant delay offset , you can set your multiplexer to give -4000ms delay or +4000ms delay depending on which way you want to shift the audio. Depending on what you used to demux, it should give you the exact value of the delay (e.g. if you used dgindex to demux it)
If it's the audio that has silence in the beginning, and the audio is actually 4s longer, you can use delaycut to trim it off
AVStoDVD should be able automate everything for you (you have the choice to use HCEnc as the encoder)
EDIT:
It appears your video & audio duration don't match
How did you get the duration? Is that from the demultiplexed files before processing (encoding) or after?Last edited by poisondeathray; 10th Feb 2011 at 18:55.
-
That can be normal if the mp4 file was muxed with the delay (I'm assuming the mp4 is in sync)
Here the container holds the delay relationship between audio & video (audio longer than video, 1st part of audio is silent)
_VVVV
AAAAA
When you demux it, the delay relationship between audio & video is lost (elementary video & audio)
VVVV
AAAAA
So if the audio is only silence at the beginning, you can use delaycut to snip it
or another approach is to mux the encoded streams with the delay value
or you can encode it together using avisynth scripts (this basically takes care of the delay, because it's read from the container), so the transcoded AC3 no longer has the gap in the beginning
aud=ffaudiosource("myvideo.mp4")
vid=ffvideosource("myvideo.mp4")
audiodub(vid,aud)
lanczosresize(720,480) #this is for ntsc
If you wanted PAL, you would need to speedup the audio & video
aud=ffaudiosource("myvideo.mp4")
vid=ffvideosource("myvideo.mp4")
audiodub(vid,aud)
lanczosresize(720,576) #this is for pal
assumefps(25, true) #this does pal speedup for both audio & video
or you can try AVStoDVD which will pretty much do everything automatically for youLast edited by poisondeathray; 10th Feb 2011 at 19:51.
-
That can be normal if the mp4 file was muxed with the delay (I'm assuming the mp4 is in sync)
Here the container holds the delay relationship between audio & video (audio longer than video, 1st part of audio is silent)
_VVVV
AAAAA
When you demux it, the delay relationship between audio & video is lost (elementary video & audio)
VVVV
AAAAA -
Try demuxing the .mp4 with dgavcindex, and the delay value should be written into the .aac audio filename
It will say something like this
BLAH T80 2_0ch 192Kbps DELAY 572ms.aac -
Is the source out of sync and/or is it in sync at the start and goes out of sync slowly getting worse near the end?
Similar Threads
-
easy way to repack or demux/remux mp4 video without re-encoding
By Drebin in forum Video ConversionReplies: 2Last Post: 31st Jan 2012, 22:01 -
Help me automating demux-remux dual audio files...
By CactusMan in forum Newbie / General discussionsReplies: 8Last Post: 6th Jan 2012, 21:59 -
Audio/video out of sync after demux-remux
By CarryNL in forum SubtitleReplies: 0Last Post: 14th Sep 2011, 15:31 -
Out-of-sync after mp4 demux
By windranger in forum Video ConversionReplies: 1Last Post: 24th Feb 2010, 18:34 -
Capture out of sync after demux/remux (framedropping)
By Bingo-days in forum CapturingReplies: 3Last Post: 13th Jan 2010, 09:41