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• WebM Video Codec in Skype 5.0 Group Video

  9 novembre 2010, par noreply@blogger.com (John Luther)

  Our friends at Skype recently released Skype 5.0 for Windows and Mac, which features a beta group video feature using VP8, the video codec in WebM. In the first half of 2010, approximately 40% of Skype-to-Skype calls were video calls and we’re excited that in the future many of those calls will be made using VP8.

  To check out the new group video feature, simply download the Skype Software.

  Note : For group video to work, everyone on the call needs the new Skype for Windows or Mac, a webcam and a broadband connection.

  For more info about Skype group video, visit the Skype website.

  

• Minimal Understanding of VP8′s Forward Transform

  16 novembre 2010, par Multimedia Mike — VP8

  Regarding my toy VP8 encoder, Pengvado mentioned in the comments of my last post, “x264 looks perfect using only i16x16 DC mode. You must be doing something wrong in computing residual or fdct or quantization.” This makes a lot of sense. The encoder generates a series of elements which describe how to reconstruct the original image. Intra block reconstruction takes into consideration the following elements :

  
  
  

  I have already verified that both my encoder and FFmpeg’s VP8 decoder agree precisely on how to reconstruct blocks based on the predictors, coefficients, and quantizers. Thus, if the decoded image still looks crazy, the elements the encoder is generating to describe the image must be wrong.

  So I started studying the forward DCT, which I had cribbed wholesale from the original libvpx 0.9.0 source code. It should be noted that the formal VP8 spec only defines the inverse transform process, not the forward process. I was using a version designated as the “short” version, vs. the “fast” version. Then I looked at the 0.9.5 FDCT. Then I got the idea of comparing the results of each.

  input:   92 91 89 86 91 90 88 86 89 89 89 88 89 87 88 93

  • libvpx 0.9.0 “short” :

    forward : -314 5 1 5 4 5 -2 0 0 1 -1 -1 1 11 -3 -4
    inverse : 92 91 89 86 89 86 91 90 91 90 88 86 88 86 89 89
    

  • libvpx 0.9.0 “fast” :

    forward : -314 4 0 5 4 4 -2 0 0 1 0 -1 1 11 -2 -5
    inverse : 91 91 89 86 88 86 91 90 91 90 88 86 88 86 89 89
    

  • libvpx 0.9.5 “short” :

    forward : -312 7 1 0 1 12 -5 2 2 -3 3 -1 1 0 -2 1
    inverse : 92 91 89 86 91 90 88 86 89 89 89 88 89 87 88 93
    

  I was surprised when I noticed that input[] != idct(fdct(input[])) in some of the above cases. Then I remembered that the aforementioned property isn’t what is meant by a “bit-exact” transform– only that all implementations of the inverse transform are supposed to produce bit-exact output for a given vector of input coefficients.

  Anyway, I tried applying each of these forward transforms. I got slightly differing results, with the latest one I tried (the fdct from libvpx 0.9.5) producing the best results (to my eye). At least the trees look better in the Big Buck Bunny logo image :

  
  
  The dense trees of the Big Buck Bunny logo using one of the libvpx 0.9.0 forward transforms
  
  
  The same segment of the image using the libvpx 0.9.5 forward transform
  

  Then again, it could be that the different numbers generated by the newer forward transform triggered different prediction modes to be chosen. Overall, adapting the newer FDCT did not dramatically improve the encoding quality.

  Working on the intra 4×4 mode encoding is generating some rather more accurate blocks than my intra 16×16 encoder. Pengvado indicated that x264 generates perfectly legible results when forcing the encoder to only use intra 16×16 mode. To be honest, I’m having trouble understanding how that can possibly occur thanks to the Walsh-Hadamard transform (WHT). I think that’s where a lot of the error is creeping in with my intra 16×16 encoder. Then again, FFmpeg implements an inverse WHT function that bears ‘vp8′ in its name. This implies that it’s custom to the algorithm and not exactly shared with H.264.

• Can ffmpeg copy parts from an rmvb file without re-encoding ?

  24 juin 2017, par Eng. M.Hamdy

  I want to fast copy parts from an rmvb file without re-encoding. This command works fine with mp4 files but not with rmbv (I dropped start time and duration here) :

  ffmpeg -i input -c copy output

  when I use it with rmvb like this :

  ffmpeg -i 1.rmvb -c copy 1.mp4

  I get this error :

  [mp4 @ 00bb8980] Could not find tag for codec rv40 in stream #0, codec
  not curre ntly supported in container Could not write header for
  output file #0 (incorrect codec parameters ?) : Invali d argument
  Stream mapping : Stream #0:1 -> #0:0 (copy) Stream #0:0 -> #0:1
  (copy)

  I also tried this :

  ffmpeg -i 1.rmvb -c copy 2.rmvb

  and got this error :

  [NULL @ 04748980] Unable to find a suitable output format for ’2.rmvb’
  2.rmvb : Invalid argument

  I tried this command :

  ffmpeg -i 1.rmvb -c:v copy -c:a aac -strict experimental -b:a 128k 1.mp4

  and got this error :

  [mp4 @ 046e0020] Could not find tag for codec rv40 in stream #0, codec
  not curre ntly supported in container Could not write header for
  output file #0 (incorrect codec parameters ?) : Invali d argument Error
  initializing output stream 0:1 — [aac @ 046e1bc0] Qavg : nan
  Conversion failed !

  I read this topic :
  but the solution does not work for me.. After many trials, this is the command that worked (and took too long time) :

  ffmpeg -i 1.rmvb -c:v libx264 -b:a 32k output.mp4

  But I do not want to re-encode the file. Any solution ?

  Edit :
  I tried :

  ffmpeg -i 1.rmvb -c copy 1.mkv

  ffmpeg version N-86447-gfeb13ae Copyright (c) 2000-2017 the FFmpeg
  developers built with gcc 7.1.0 (GCC) configuration : —enable-gpl
  —enable-version3 —enable-cuda —enable-cuvid —e nable-d3d11va —enable-dxva2 —enable-libmfx —enable-nvenc —enable-avisynth — enable-bzlib —enable-fontconfig —enable-frei0r —enable-gnutls
  —enable-iconv
  —enable-libass —enable-libbluray —enable-libbs2b —enable-libcaca —enable-li bfreetype —enable-libgme —enable-libgsm —enable-libilbc —enable-libmodplug -
  -enable-libmp3lame —enable-libopencore-amrnb —enable-libopencore-amrwb —enabl e-libopenh264 —enable-libopenjpeg —enable-libopus —enable-librtmp —enable-li bsnappy —enable-libsoxr —enable-libspeex —enable-libtheora —enable-libtwolam e —enable-libvidstab —enable-libvo-amrwbenc —enable-libvorbis —enable-libvpx —enable-libwavpack —enable-libwebp —enable-libx264 —enable-libx265 —enable
  -libxavs —enable-libxvid —enable-libzimg —enable-lzma —enable-zlib libavutil 55. 63.100 / 55. 63.100 libavcodec 57. 98.100 /
  57. 98.100 libavformat 57. 73.100 / 57. 73.100 libavdevice 57. 7.100 / 57. 7.100 libavfilter 6. 92.100 / 6. 92.100 libswscale 4. 7.101 / 4. 7.101 libswresample 2. 8.100 /
  2. 8.100 libpostproc 54. 6.100 / 54. 6.100 [rm @ 033a7520] Invalid stream index 2 for index at pos 206099254 Input #0, rm, from
  ’1.rmvb’ : Metadata :
  title : ArabSeed.CoM
  author : ArabSeed.CoM
  copyright : ArabSeed.CoM
  comment :
  ASMRuleBook : #($Bandwidth >= 0),Stream0Bandwidth = 64082, Stream1Bandwi dth = 285918 ;
  Audiences : Easy RealMedia Tool’s Audience ;
  audioMode : music
  Creation Date : 4/22/2010 4:31:14
  Description : This File is Created by Easy RealMedia Tools@ !
  Email : rick@redcheek.net
  Generated By : Easy RealMedia Tools V1.8x
  HomeWeb : http://redcheek.net
  Keywords : ArabSeed.CoM
  Modification Date : 4/22/2010 4:31:14
  videoMode : normal Duration : 01:16:35.69, start : 0.000000, bitrate : 358 kb/s
  Stream #0:0 : Audio : cook (cook / 0x6B6F6F63), 44100 Hz, stereo, fltp, 64 kb/ s
  Stream #0:1 : Video : rv40 (RV40 / 0x30345652), yuv420p, 720x408, 280 kb/s, 25 fps, 25 tbr, 1k tbn, 1k tbc Output #0, matroska, to
  ’1.mkv’ : Metadata :
  title : ArabSeed.CoM
  author : ArabSeed.CoM
  copyright : ArabSeed.CoM
  comment :
  ASMRuleBook : #($Bandwidth >= 0),Stream0Bandwidth = 64082, Stream1Bandwi dth = 285918 ;
  Audiences : Easy RealMedia Tool’s Audience ;
  audioMode : music
  Creation Date : 4/22/2010 4:31:14
  Description : This File is Created by Easy RealMedia Tools@ !
  Email : rick@redcheek.net
  Generated By : Easy RealMedia Tools V1.8x
  HomeWeb : http://redcheek.net
  Keywords : ArabSeed.CoM
  Modification Date : 4/22/2010 4:31:14
  videoMode : normal
  encoder : Lavf57.73.100
  Stream #0:0 : Video : rv40 (RV40 / 0x30345652), yuv420p, 720x408, q=2-31, 280 kb/s, 25 fps, 25 tbr, 1k tbn, 1k tbc
  Stream #0:1 : Audio : cook ([255][255][255][255] / 0xFFFFFFFF), 44100 Hz, ster eo, fltp, 64 kb/s Stream mapping : Stream #0:1 -> #0:0
  (copy) Stream #0:0 -> #0:1 (copy) Press [q] to stop, [?] for help
  [matroska @ 05228980] The Matroska muxer does not yet support muxing
  cook av_interleaved_write_frame() : Not yet implemented in FFmpeg,
  patches welcome Error writing trailer of 1.mkv : Not yet implemented in
  FFmpeg, patches welcome frame= 21 fps=0.0 q=-1.0 Lsize= 0kB
  time=00:00:01.48 bitrate= 0.0kbits /s speed= 148x video:2kB
  audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing ove
  rhead : unknown Conversion failed !

  I also tried :

  ffmpeg -i 1.rmvb -c copy 1.avi
  
  
  
  ffmpeg version N-86447-gfeb13ae Copyright (c) 2000-2017 the FFmpeg developers
  
    built with gcc 7.1.0 (GCC)
  
    configuration: --enable-gpl --enable-version3 --enable-cuda --enable-cuvid --e
  
  nable-d3d11va --enable-dxva2 --enable-libmfx --enable-nvenc --enable-avisynth --
  
  enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv
  
  --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-li
  
  bfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug -
  
  -enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enabl
  
  e-libopenh264 --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-li
  
  bsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolam
  
  e --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx
  
   --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable
  
  -libxavs --enable-libxvid --enable-libzimg --enable-lzma --enable-zlib
  
    libavutil      55. 63.100 / 55. 63.100
  
    libavcodec     57. 98.100 / 57. 98.100
  
    libavformat    57. 73.100 / 57. 73.100
  
    libavdevice    57.  7.100 / 57.  7.100
  
    libavfilter     6. 92.100 /  6. 92.100
  
    libswscale      4.  7.101 /  4.  7.101
  
    libswresample   2.  8.100 /  2.  8.100
  
    libpostproc    54.  6.100 / 54.  6.100
  
  [rm @ 00077520] Invalid stream index 2 for index at pos 206099254
  
  Input #0, rm, from '1.rmvb':
  
    Metadata:
  
      title           : ArabSeed.CoM
  
      author          : ArabSeed.CoM
  
      copyright       : ArabSeed.CoM
  
      comment         :
  
      ASMRuleBook     : #($Bandwidth >= 0),Stream0Bandwidth = 64082, Stream1Bandwi
  
  dth = 285918;
  
      Audiences       : Easy RealMedia Tool's Audience;
  
      audioMode       : music
  
      Creation Date   : 4/22/2010 4:31:14
  
      Description     : This File is Created by Easy RealMedia Tools@!
  
      Email           : rick@redcheek.net
  
      Generated By    : Easy RealMedia Tools V1.8x
  
      HomeWeb         : http://redcheek.net
  
      Keywords        : ArabSeed.CoM
  
      Modification Date: 4/22/2010 4:31:14
  
      videoMode       : normal
  
    Duration: 01:16:35.69, start: 0.000000, bitrate: 358 kb/s
  
      Stream #0:0: Audio: cook (cook / 0x6B6F6F63), 44100 Hz, stereo, fltp, 64 kb/
  
  s
  
      Stream #0:1: Video: rv40 (RV40 / 0x30345652), yuv420p, 720x408, 280 kb/s, 25
  
   fps, 25 tbr, 1k tbn, 1k tbc
  
  Could not write header for output file #0 (incorrect codec parameters ?): Operat
  
  ion not permitted
  
  Stream mapping:
  
    Stream #0:1 -> #0:0 (copy)
  
    Stream #0:0 -> #0:1 (copy)
  
      Last message repeated 1 times