Gentoo Archives: gentoo-user

From: Dale <rdalek1967@×××××.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 08:56:03
In Reply to: Re: [gentoo-user] Video editing advice on formats and size of file by Michael Mol
1 Michael Mol wrote:
2 > This is a slightly simplified explanation, owing to my probably not
3 > remembering details quite correctly.
4 >
5 > Media files consist of at least three parts: The container format, the
6 > audio stream and the video stream. You're familiar with container
7 > formats as ".flv", ".mkv", ".avi", ".mpg", ".mp4", etc.
8 >
9 > The audio and video streams consist of frames (for video) or samples
10 > (for audio) where each one consists of information particular to a
11 > particular video image or audio sample. The audio and video frames
12 > typically don't include information as to when they occurred; a frame
13 > won't tell you that it's specific to 33.2 seconds into a sequence, for
14 > example.
15 >
16 > Normally, the file and/or streams will describe how many frames per
17 > second the video stream should move along at, and how many samples per
18 > second the audio stream should move along.
19 >
20 > When the samples and frames stop matching up as the media file plays,
21 > you get desync. This is normal to within a certain tolerance; when
22 > you're moving along 48k audio samples per second, and only 30 video
23 > frames per second, nobody cares if an audio sample is ten or so off
24 > from its ideal position.
25 >
26 > Unfortunately, I can only tell you what's going on. I can't tell you
27 > how to fix it; it's not something I dealt with much.
28 >
29 > I'd suggest you give the other tools a try, too. The other tools
30 > brought up will do essentially the same thing as avidemux; they're
31 > just ripping the audio and video streams out of the source container
32 > files and placing them into a new container file. Your old approach
33 > was very, very slow because your tools were generating completely new
34 > audio and video streams. It's the difference between "dd if=src
35 > of=dst" and "dd if=src|lzma --decompress --stdout|lzma --stdout|dd
36 > of=dst" ... except lzma doesn't loose any data in the process, while
37 > your transcoding was. Once you get the sync issues worked out, you
38 > might even notice improvements in audio and image quality. :)
39 >
41 I been doing some testing on this. I went to about the end of a 3 hour
42 video. By the time it gets near the end of the video, the sound is
43 almost 1.4 seconds off. I tested this by telling smplayer to adjust the
44 audio delay. It is a bit annoying to see something on screen then hear
45 it a second or so later. It's like seeing a explosion at a distance.
46 You see it then have to wait for the sound wave to hit you. When I am
47 midways of the video, it is about .6 to .7 seconds off. So, it gets
48 farther off as it goes. It's most likely one step off that just gets
49 worse as it goes.
51 I tried a couple other commands but I get errors about the file type. I
52 think a couple movies are in flv1 which is old. I may have to convert
53 them then stitch them together, which may not do the sound any good then
54 either. lol
56 Well, I got something to play with.
58 Dale
60 :-) :-)
62 --
63 I am only responsible for what I said ... Not for what you understood or how you interpreted my words!
65 Miss the compile output? Hint:
66 EMERGE_DEFAULT_OPTS="--quiet-build=n"


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