IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
[Help] Demux audio from m2ts not the same using diff app
redwine
post Dec 17 2011, 21:24
Post #1





Group: Members
Posts: 23
Joined: 21-June 11
Member No.: 91712



Hi,

I have a m2ts file with video and LCPM audio.
I tried to demux the LPCM audio stream using TsMuxer, VLC & Audacity (open m2ts and export as wave).
I notice that all the 3 app give me wave file that are slightly different from one another.
(but all 3 apps give me 16bit 48kHz wave)

For a start, file size are slight different.
When i open the wave file in Audacity, the waveform are slightly different as well.
If i perform a binary compare, the whole files are totally different.
(if its a offset issue, i normally only see differences at the start or end of the file)

Any possibility of the above apps processing the raw audio differently ?


Rgds
Go to the top of the page
+Quote Post
DVDdoug
post Dec 19 2011, 21:21
Post #2





Group: Members
Posts: 2441
Joined: 24-August 07
From: Silicon Valley
Member No.: 46454



Strange... I don't know how the audio data would get changed. It's not easy to alter PCM audio data "accidently" without really fouling-up the audio... Do these files sound similar?

If the files sound the same, I wouldn't worry about it. If they sound different, choose the best-sounding one. tongue.gif

I think foobar2000 can compare the audio data (or get a checksum of the audio) while ignoring the file header. (I don't use foobar, so someone else can help with that... assuming it's actually possible.)

QUOTE
I have a m2ts file with video and LCPM audio.
Is there possibly more than one audio stream? (Like a file from a DVD with both LPCM and Dolby AC3 streams?) Audacity (and I think VLC) should be able to open various formats and save them as WAV. I'm not sure if TsMuxer can convert, but a simple de-muxer should simply be making an m2a file... If it's making a WAV file, it's doing more than de-muxing... but it should be just writing a header followed by the original PCM data.

QUOTE
For a start, file size are slight different.
That could simply be a difference in the header, or perhaps some silence-padding on the end, depending on how the MPEG frames are decoded.

QUOTE
When i open the wave file in Audacity, the waveform are slightly different as well.
How are they different? If you can see a difference, you should be able to hear a difference....

QUOTE
If i perform a binary compare, the whole files are totally different.
(if its a offset issue, i normally only see differences at the start or end of the file)
If there's an offset, all of the bytes will be offset and a binary compare will show at all bytes are different. If I compare ABCD to xxABCD, the 3rd element in the 1st series is 'C' and the 3rd element in the 2nd series is 'A'. None of the data matches. (All of the data after whatever is causing the offset will be mis-matched.)
Go to the top of the page
+Quote Post
killazys
post Mar 10 2012, 15:25
Post #3





Group: Members
Posts: 7
Joined: 25-August 11
Member No.: 93266



Use http://hank315.nl/ DGMPGDecode package. DGDecode should demux to a .pcm file for you. You can then convert that using SoX, NicLPCMSource() + SoundOut() in Avisynth, etc.
Go to the top of the page
+Quote Post

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 20th April 2014 - 00:11