Gentoo Archives: gentoo-user

From: Michael Mol <mikemol@×××××.com>
To: gentoo-user@l.g.o
Subject: Re: [gentoo-user] Video editing advice on formats and size of file
Date: Sat, 24 Dec 2011 03:51:35
In Reply to: Re: [gentoo-user] Video editing advice on formats and size of file by Dale
1 On Fri, Dec 23, 2011 at 10:26 PM, Dale <rdalek1967@×××××.com> wrote:
2 > Dale wrote:
3 >>
4 >>
5 >> Well, it took some experimenting but I finally figured it out.  I like to
6 >> have never found the save video option under the file menu.  Why not hide it
7 >> next time.  lol  I can't blame it on my glasses this time either.  I got new
8 >> ones a while back.  Maybe it is stupidity.  o_O
9 >>
10 >> I will say this tho, it is dang fast.  It took like 10 to 15 seconds and
11 >> it was done.  Kdenlive took MUCH longer.
12 >>
13 >> File size is awesome too.  The two files added are very close to just
14 >> adding the file size of each video.  I'm talking within a megabyte or two.
15 >>
16 >> Thanks for this tip.  I got a new toy to play with.  lol
17 >>
18 >> Dale
19 >>
20 >> :-)  :-)
21 >>
22 >
23 > Since you seem to have used this more than I have.  I have a question.  On
24 > the original videos, the sound is synced up fine.  The words match when
25 > their lips move and other sounds match up.  After I splice them together,
26 > the sound is off.  It seems longer videos are worse than shorter ones.  Am I
27 > missing something here?  I'm pretty much using the default settings.
28 >
29 > I also have a problem with the older .flv1 files.  Any tips on that?
30 >  Something special I need to install for older formats?  I googled and found
31 > threads but it appears the packages either merged with something else or are
32 > no longer available or something.
33 >
34 > Thanks much.
36 This is a slightly simplified explanation, owing to my probably not
37 remembering details quite correctly.
39 Media files consist of at least three parts: The container format, the
40 audio stream and the video stream. You're familiar with container
41 formats as ".flv", ".mkv", ".avi", ".mpg", ".mp4", etc.
43 The audio and video streams consist of frames (for video) or samples
44 (for audio) where each one consists of information particular to a
45 particular video image or audio sample. The audio and video frames
46 typically don't include information as to when they occurred; a frame
47 won't tell you that it's specific to 33.2 seconds into a sequence, for
48 example.
50 Normally, the file and/or streams will describe how many frames per
51 second the video stream should move along at, and how many samples per
52 second the audio stream should move along.
54 When the samples and frames stop matching up as the media file plays,
55 you get desync. This is normal to within a certain tolerance; when
56 you're moving along 48k audio samples per second, and only 30 video
57 frames per second, nobody cares if an audio sample is ten or so off
58 from its ideal position.
60 Unfortunately, I can only tell you what's going on. I can't tell you
61 how to fix it; it's not something I dealt with much.
63 I'd suggest you give the other tools a try, too. The other tools
64 brought up will do essentially the same thing as avidemux; they're
65 just ripping the audio and video streams out of the source container
66 files and placing them into a new container file. Your old approach
67 was very, very slow because your tools were generating completely new
68 audio and video streams. It's the difference between "dd if=src
69 of=dst" and "dd if=src|lzma --decompress --stdout|lzma --stdout|dd
70 of=dst" ... except lzma doesn't loose any data in the process, while
71 your transcoding was. Once you get the sync issues worked out, you
72 might even notice improvements in audio and image quality. :)
74 --
75 :wq


Subject Author
Re: [gentoo-user] Video editing advice on formats and size of file Dale <rdalek1967@×××××.com>
Re: [gentoo-user] Video editing advice on formats and size of file David Haller <gentoo@×××××××.de>