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• Lossless avi encoding on linux

  31 août 2012, par JohnSavage

  I am trying to write video using opencv. It is important for me to do this precisely - so it has to be a lossless codec. I am working with OpenCV 2.4.1 on Ubuntu 12.04

  Previously, I was using the fourcc code 0. This gave me the exact result I wanted, and I was able to recover the images perfectly.

  I am not sure what happened, but as of a recent update (around Jul 20th 2012), something went wrong and I am no longer able to write files with this fourcc code. I really don't remember what it was, but it could have come from doing an update, removing some software from my software center, and some other things I did during general cleaning...

  When I check an older file with mediainfo (http://www.fourcc.org/identifier/) I see the following result :

  Complete name                            : oldsample.avi
  
  Format                                   : AVI
  
  Format/Info                              : Audio Video Interleave
  
  Format profile                           : OpenDML
  
  File size                                : 1.07 GiB
  
  Duration                                 : 41s 467ms
  
  Overall bit rate                         : 221 Mbps
  
  Writing application                      : Lavf53.5.0
  
  Video
  
  ID                                       : 0
  
  Format                                   : RGB
  
  Codec ID                                 : 0x00000000
  
  Codec ID/Info                            : Basic Windows bitmap format. 1, 4 and 8 bpp     versions are palettised. 16, 24 and 32bpp contain raw RGB samples
  
  Duration                                 : 41s 467ms
  
  Bit rate                                 : 221 Mbps
  
  Width                                    : 640 pixels
  
  Height                                   : 4294966 816 pixels
  
  Display aspect ratio                     : 0.000
  
  Frame rate                               : 30.000 fps
  
  Bit depth                                : 8 bits
  
  Stream size                              : 1.07 GiB (100%)

  Now, I see that when I write using the 0 fourcc codec, the program actually defaults to the i420 codec. Here is the output from one of the files I try to write now :

  Complete name                            : newsample.avi
  
  Format                                   : AVI
  
  Format/Info                              : Audio Video Interleave
  
  File size                                : 73.0 MiB
  
  Duration                                 : 5s 533ms
  
  Overall bit rate                         : 111 Mbps
  
  Writing application                      : Lavf54.6.100
  
  Video
  
  ID                                       : 0
  
  Format                                   : YUV
  
  Codec ID                                 : I420
  
  Codec ID/Info                            : 8 bit Y plane followed by 8 bit 2x2 subsampled U and V planes.
  
  Duration                                 : 5s 533ms
  
  Bit rate                                 : 111 Mbps
  
  Width                                    : 640 pixels
  
  Height                                   : 480 pixels
  
  Display aspect ratio                     : 4:3
  
  Frame rate                               : 30.000 fps
  
  Compression mode                         : Lossless
  
  Bits/(Pixel*Frame)                       : 12.000
  
  Stream size                              : 72.9 MiB (100%)

  This format, and other formats I try to use (like huffyuv HFYU), do not work for me because I end up with effects like this http://imgur.com/a/0OC4y - you see the bright artifacts coming in due to what I assume is either lossy compression or chroma subsampling in the case of HFYU which is supposed to be lossless. What you are looking at is the red channel from one of my videos. The perceptual effect is negligible when you look at all 3 channels simultaneously but it is essential that I reconstruct the images exactly.

  Furthermore, while I am able to play my old files in media players like vlc, I suddenly find them to be completely incompatible with opencv. When I try to open the older files with a videocapture, the open step works fine, but trying to do a read operation results in a segfault. Furthermore, When I try to write with either :

  CV_FOURCC(0,0,0,0)
  
  0

  Opencv defaults to I420 for some reason.

  Next, I tried using some alternate codecs. 'DIB ' seems like something that should work for me, and on the opencv website (http://opencv.willowgarage.com/wiki/VideoCodecs) it is listed as a 'recommended' codec. However, trying to use this results in the following message :

  OpenCV-2.4.1/modules/highgui/src/cap_gstreamer.cpp:483: error: (-210) Gstreamer Opencv backend doesn't support this codec acutally. in function CvVideoWriter_GStreamer::open
  
  
  
  Aborted (core dumped)

  I checked the opencv source for this codec, and stumbled across the following :

  cd OpenCV-2.4.1/modules
  
  grep -i -r "CV_FOURCC" ./*
  
  ...
  
  ./highgui/src/cap_qt.cpp:    /*if( fourcc == CV_FOURCC( 'D', 'I', 'B', ' ' ))
  
  ./highgui/include/opencv2/highgui/highgui_c.h:#define CV_FOURCC_DEFAULT CV_FOURCC('I', 'Y', 'U', 'V') /* Use default codec for specified filename (Linux only) */

  I tried installing qt4 and reconfiguring with the WITH_QT flag, but that did not change anything. I also tried uncommenting that part of the code and reinstalling opencv, but that also did not work.

  My ultimate goal is for any way to efficiently store and retrieve a video stream with 16 bits for every pixel (like 32float would work fine, and then it wouldn't need to be perfect). Right now I am unpacking the 16 bits into the red and green channels, which is why I need it to be perfect - since an error of 1 in the red channel is multiplied by 256 in the final result. I am not having success with any of the fourcc codes available to me.

• Révision 21861 : Report de r21860

  10 décembre 2014, par kent1 -

  Le Dari (http://fr.wikipedia.org/wiki/Dari) est aussi une langue rtl

• Winamp and the March of GUI

  1er juillet 2012, par Multimedia Mike — General, ars technica, gui, user interface, winamp

  Ars Technica recently published a 15-year retrospective on the venerable Winamp multimedia player, prompting bouts of nostalgia and revelations of "Huh ? That program is still around ?" from many readers. I was among them.

  
  
  

  I remember first using Winamp in 1997. I remember finding a few of these new files called MP3s online and being able to play the first 20 seconds using the official Fraunhofer Windows player— full playback required the fully licensed version. Then I searched for another player and came up with Winamp. The first version I ever used was v1.05 in the summer of 1997. I remember checking the website often for updates and trying out every single one. I can’t imagine doing that nowadays— programs need to auto-update themselves (which Winamp probably does now ; I can’t recall the last time I used the program).

  Video Underdog
  The last time Winamp came up on my radar was early in 2003 when a new version came with support for a custom, proprietary multimedia audio/video format called Nullsoft Video (NSV). I remember the timeframe because the date is indicated in the earliest revision of my NSV spec document (back when I was maintaining such docs in a series of plaintext files). This was cobbled together from details I and others in the open source multimedia community sorted out from sample files. It was missing quite a few details, though.

  Then, Winamp founder Justin Frankel — introduced through a colleague on the xine team — emailed me his official NSV format and told me I was free to incorporate details into my document just as long as it wasn’t obvious that I had the official spec. This put me in an obnoxious position of trying to incorporate details which would have been very difficult to reverse engineer without the official doc. I think I coped with the situation by never really getting around to updating my doc in any meaningful way. Then, one day, the official spec was released to the world anyway, and it is now mirrored here at multimedia.cx.

  I don’t think the format ever really caught on in any meaningful way, so not a big deal. (Anytime I say that about a format, I always learn it saw huge adoption is some small but vocal community.)

  What’s Wrong With This Picture ?
  What I really wanted to discuss in this post was the matter of graphical user interfaces and how they have changed in the last 15 years.
  
  I still remember when I first downloaded Winamp v1.05 and tried it on my Windows machine at the time. Indignantly, the first thought I had was, "What makes this program think it’s so special that it’s allowed to violate the user interface conventions put forth by the rest of the desktop ?" All of the Windows programs followed a standard set of user interface patterns and had a consistent look and feel... and then Winamp came along and felt it could violate all those conventions.

  I guess I let the program get away with it because it was either that or only play 20-second clips from the unregistered Fraunhofer player. Though incredibly sterile by comparison, the Fraunhofer player, it should be noted, followed Windows UI guidelines to the letter.

  As the summer of 1997 progressed and more Winamp versions were released, eventually one came out (I think it was v1.6 or so) that supported skins. I was excited because there was a skin that made the program look like a proper Windows program— at least if you used the default Windows color scheme, and had all of your fonts a certain type and size.

  Skins were implemented by packaging together a set of BMP images to overlay on various UI elements. I immediately saw a number of shortcomings with this skinning approach. A big one was UI lock-in. Ironically, if you skin an app and wish to maintain backwards compatibility with the thousands of skins selflessly authored by your vibrant community (seriously, I couldn’t believe how prolific these things were), then you were effectively locked into the primary UI. Forget about adding a new button anywhere.

  Another big problem was resolution-independence. Basing your UI on static bitmaps doesn’t scale well with various resolutions. Winamp had its normal mode and it also had double-sized mode.

  Skins proliferated among many types of programs in the late 1990s. I always treasured this Suck.com (remember them ? that’s a whole other nostalgia trip) essay from April, 2000 entitled Skin Cancer. Still, Winamp was basically the standard, and the best, and I put away my righteous nerd rage and even dug through the vast troves of skins. I remember settling on Swankamp for a good part of 1998, probably due to the neo-swing revival at the time.

  
  
  

  Then again, if Winamp irked me, imagine my reaction when I was first exposed to the Sonique Music Player in 1998 :

  
  
  

  The New UI Order
  Upon reflection, I realize now that I had a really myopic view of what a computer GUI should be. I thought the GUIs were necessarily supposed to follow the WIMP (windows, icons, mouse, pointer) paradigm and couldn’t conceive of anything different. For a long time, I couldn’t envision a useful GUI on a small device (like a phone) because WIMP didn’t fit well on such a small interface (even though I saw various ill-fated attempts to make it work). This thinking seriously crippled me when I was trying to craft a GUI for a custom console media player I was developing as a hobby many years ago.

  I’m looking around at what I have open on my Windows 7 desktop right now. Google Chrome browser, Apple iTunes, Adobe Photoshop Elements, and VMware Player are 4 programs which all seem to have their own skins. Maybe Winamp doesn’t look so out of place these days.