Recherche avancée

Sur d’autres sites (9919)

• H.264 and VP8 for still image coding : WebP ?

  1er octobre 2010, par Dark Shikari — H.264, VP8, google, psychovisual optimizations

  JPEG is a very old lossy image format. By today’s standards, it’s awful compression-wise : practically every video format since the days of MPEG-2 has been able to tie or beat JPEG at its own game. The reasons people haven’t switched to something more modern practically always boil down to a simple one — it’s just not worth the hassle. Even if JPEG can be beaten by a factor of 2, convincing the entire world to change image formats after 20 years is nigh impossible. Furthermore, JPEG is fast, simple, and practically guaranteed to be free of any intellectual property worries. It’s been tried before : JPEG-2000 first, then Microsoft’s JPEG XR, both tried to unseat JPEG. Neither got much of anywhere.

  Now Google is trying to dump yet another image format on us, “WebP”. But really, it’s just a VP8 intra frame. There are some obvious practical problems with this new image format in comparison to JPEG ; it doesn’t even support all of JPEG’s features, let alone many of the much-wanted features JPEG was missing (alpha channel support, lossless support). It only supports 4:2:0 chroma subsampling, while JPEG can handle 4:2:2 and 4:4:4. Google doesn’t seem interested in adding any of these features either.

  But let’s get to the meat and see how these encoders stack up on compressing still images. As I explained in my original analysis, VP8 has the advantage of H.264′s intra prediction, which is one of the primary reasons why H.264 has such an advantage in intra compression. It only has i4x4 and i16x16 modes, not i8x8, so it’s not quite as fancy as H.264′s, but it comes close.

  The test files are all around 155KB ; download them for the exact filesizes. For all three, I did a binary search of quality levels to get the file sizes close. For x264, I encoded with --tune stillimage --preset placebo. For libvpx, I encoded with --best. For JPEG, I encoded with ffmpeg, then applied jpgcrush, a lossless jpeg compressor. I suspect there are better JPEG encoders out there than ffmpeg ; if you have one, feel free to test it and post the results. The source image is the 200th frame of Parkjoy, from derf’s page (fun fact : this video was shot here ! More info on the video here.).

  Files : (x264 [154KB], vp8 [155KB], jpg [156KB])

  Results (decoded to PNG) : (x264, vp8, jpg)

  This seems rather embarrassing for libvpx. Personally I think VP8 looks by far the worst of the bunch, despite JPEG’s blocking. What’s going on here ? VP8 certainly has better entropy coding than JPEG does (by far !). It has better intra prediction (JPEG has just DC prediction). How could VP8 look worse ? Let’s investigate.

  VP8 uses a 4×4 transform, which tends to blur and lose more detail than JPEG’s 8×8 transform. But that alone certainly isn’t enough to create such a dramatic difference. Let’s investigate a hypothesis — that the problem is that libvpx is optimizing for PSNR and ignoring psychovisual considerations when encoding the image… I’ll encode with --tune psnr --preset placebo in x264, turning off all psy optimizations. 

  Files : (x264, optimized for PSNR [154KB]) [Note for the technical people : because adaptive quantization is off, to get the filesize on target I had to use a CQM here.]

  Results (decoded to PNG) : (x264, optimized for PSNR)

  What a blur ! Only somewhat better than VP8, and still worse than JPEG. And that’s using the same encoder and the same level of analysis — the only thing done differently is dropping the psy optimizations. Thus we come back to the conclusion I’ve made over and over on this blog — the encoder matters more than the video format, and good psy optimizations are more important than anything else for compression. libvpx, a much more powerful encoder than ffmpeg’s jpeg encoder, loses because it tries too hard to optimize for PSNR.

  These results raise an obvious question — is Google nuts ? I could understand the push for “WebP” if it was better than JPEG. And sure, technically as a file format it is, and an encoder could be made for it that’s better than JPEG. But note the word “could”. Why announce it now when libvpx is still such an awful encoder ? You’d have to be nuts to try to replace JPEG with this blurry mess as-is. Now, I don’t expect libvpx to be able to compete with x264, the best encoder in the world — but surely it should be able to beat an image format released in 1992 ?

  Earth to Google : make the encoder good first, then promote it as better than the alternatives. The reverse doesn’t work quite as well.

  [155KB]

• FFMEG dumping a RTSP streaming works on Windows but not in Ubuntu

  8 août 2016, par cuentafalsa7

  I have a camera with a RTSP server. When I try to save the streaming, using FFMPEG in Windows works ; in Ubuntu, FFMPEG it doesn’t.

  The command, in Windows is :

  ffmpeg.exe -i "rtsp://192.168.1.10:1236/?videoapi=mc&h264=1000-20-1280-960" -r 20 test.mp4

  In Linux :

  ffmpeg -i "rtsp://192.168.1.10:1236/?videoapi=mc&h264=1000-20-1280-960" -r 20 test.mp4

  The output in Linux is :

  $ ffmpeg  -i "rtsp://192.168.1.10:1236/?videoapi=mr&h264=1000-20-1280-960" -r 20 test.mp4
  
  ffmpeg version 2.8.6-1ubuntu2 Copyright (c) 2000-2016 the FFmpeg developers                                                                                                                                                                                                    
  
    built with gcc 5.3.1 (Ubuntu 5.3.1-11ubuntu1) 20160311                                                                                                                                                                                                                       
  
    configuration: --prefix=/usr --extra-version=1ubuntu2 --build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --cc=cc --cxx=g++ --enable-gpl --enable-shared --disable-stripping --disable-decoder=libopenjpeg --disable-decoder=libschroedinger --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-libzmq --enable-frei0r --enable-libx264 --enable-libopencv                                                                                                                                                                                                                                            
  
    libavutil      54. 31.100 / 54. 31.100                                                                                                                                                                                                                                       
  
    libavcodec     56. 60.100 / 56. 60.100                                                                                                                                                                                                                                       
  
    libavformat    56. 40.101 / 56. 40.101                                                                                                                                                                                                                                       
  
    libavdevice    56.  4.100 / 56.  4.100                                                                                                                                                                                                                                       
  
    libavfilter     5. 40.101 /  5. 40.101                                                                                                                                                                                                                                       
  
    libavresample   2.  1.  0 /  2.  1.  0                                                                                                                                                                                                                                       
  
    libswscale      3.  1.101 /  3.  1.101                                                                                                                                                                                                                                       
  
    libswresample   1.  2.101 /  1.  2.101                                                                                                                                                                                                                                       
  
    libpostproc    53.  3.100 / 53.  3.100                                                                                                                                                                                                                                       
  
  [rtsp @ 0x1f18340] UDP timeout, retrying with TCP                                                                                                                                                                                                                              
  
  [rtsp @ 0x1f18340] Nonmatching transport in server reply                                                                                                                                                                                                                       
  
  [rtsp @ 0x1f18340] Could not find codec parameters for stream 0 (Video: h264, none): unspecified size                                                                                                                                                                          
  
  Consider increasing the value for the 'analyzeduration' and 'probesize' options                                                                                                                                                                                                
  
  rtsp://192.168.1.10:1236/?videoapi=mr&h264=1000-20-1280-960: could not find codec parameters                                                                                                                                                                                  
  
  Input #0, rtsp, from 'rtsp://192.168.1.10:1236/?videoapi=mr&h264=1000-20-1280-960':                                                                                                                                                                                           
  
    Metadata:                                                                                                                                                                                                                                                                    
  
      title           : Unnamed                                                                                                                                                                                                                                                  
  
      comment         : N/A                                                                                                                                                                                                                                                      
  
    Duration: N/A, bitrate: N/A                                                                                                                                                                                                                                                  
  
      Stream #0:0: Video: h264, none, 90k tbr, 90k tbn, 180k tbc                                                                                                                                                                                                                 
  
  Output #0, mp4, to 'test.mp4':                                                                                                                                                                                                                                                 
  
  Output file #0 does not contain any stream              

  The ffmpeg.exe output is :

  >ffmpeg.exe
  
  ffmpeg version N-81300-gce2217b Copyright (c) 2000-2016 the FFmpeg developers
  
    built with gcc 5.4.0 (GCC)
  
    configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-dxva2 --enable-libmfx --enable-nvenc --enable-avisynth --enable-bzlib --enable-lib
  
  ebur128 --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libfree
  
  type --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-lib
  
  openjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame
  
   --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-decklink --enable-zlib
  
    libavutil      55. 28.100 / 55. 28.100
  
    libavcodec     57. 51.100 / 57. 51.100
  
    libavformat    57. 46.100 / 57. 46.100
  
    libavdevice    57.  0.102 / 57.  0.102
  
    libavfilter     6. 50.100 /  6. 50.100
  
    libswscale      4.  1.100 /  4.  1.100
  
    libswresample   2.  1.100 /  2.  1.100
  
    libpostproc    54.  0.100 / 54.  0.100
  
  Hyper fast Audio and Video encoder
  
  usage: ffmpeg [options] [[infile options] -i infile]... {[outfile options] outfile}...
  
  
  
  Use -h to get full help or, even better, run 'man ffmpeg'

  The ffmpeg output in Ubuntu is :

  $ ffmpeg 
  
  ffmpeg version 2.8.6-1ubuntu2 Copyright (c) 2000-2016 the FFmpeg developers                                                                                                                                                                                                    
  
    built with gcc 5.3.1 (Ubuntu 5.3.1-11ubuntu1) 20160311                                                                                                                                                                                                                       
  
    configuration: --prefix=/usr --extra-version=1ubuntu2 --build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --cc=cc --cxx=g++ --enable-gpl --enable-shared --disable-stripping --disable-decoder=libopenjpeg --disable-decoder=libschroedinger --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-libzmq --enable-frei0r --enable-libx264 --enable-libopencv                                                                                                                                                                                                                                            
  
    libavutil      54. 31.100 / 54. 31.100                                                                                                                                                                                                                                       
  
    libavcodec     56. 60.100 / 56. 60.100                                                                                                                                                                                                                                       
  
    libavformat    56. 40.101 / 56. 40.101                                                                                                                                                                                                                                       
  
    libavdevice    56.  4.100 / 56.  4.100                                                                                                                                                                                                                                       
  
    libavfilter     5. 40.101 /  5. 40.101                                                                                                                                                                                                                                       
  
    libavresample   2.  1.  0 /  2.  1.  0                                                                                                                                                                                                                                       
  
    libswscale      3.  1.101 /  3.  1.101                                                                                                                                                                                                                                       
  
    libswresample   1.  2.101 /  1.  2.101                                                                                                                                                                                                                                       
  
    libpostproc    53.  3.100 / 53.  3.100                                                                                                                                                                                                                                       
  
  Hyper fast Audio and Video encoder                                                                                                                                                                                                                                             
  
  usage: ffmpeg [options] [[infile options] -i infile]... {[outfile options] outfile}...                                                                                                                                                                                         
  
  
  
  Use -h to get full help or, even better, run 'man ffmpeg'  

  I’m using Windows 7 64 bits and Ubuntu 16.04.

  I have tried to increase the suggested values but didn’t work either.
  Any idea, except switching to Windows ?

• H.264 and VP8 for still image coding : WebP ?

  
  1er octobre 2010, par Dark Shikari — google, H.264, psychovisual optimizations, VP8

  Update : post now contains a Theora comparison as well ; see below.

  JPEG is a very old lossy image format. By today’s standards, it’s awful compression-wise : practically every video format since the days of MPEG-2 has been able to tie or beat JPEG at its own game. The reasons people haven’t switched to something more modern practically always boil down to a simple one — it’s just not worth the hassle. Even if JPEG can be beaten by a factor of 2, convincing the entire world to change image formats after 20 years is nigh impossible. Furthermore, JPEG is fast, simple, and practically guaranteed to be free of any intellectual property worries. It’s been tried before : JPEG-2000 first, then Microsoft’s JPEG XR, both tried to unseat JPEG. Neither got much of anywhere.

  Now Google is trying to dump yet another image format on us, “WebP”. But really, it’s just a VP8 intra frame. There are some obvious practical problems with this new image format in comparison to JPEG ; it doesn’t even support all of JPEG’s features, let alone many of the much-wanted features JPEG was missing (alpha channel support, lossless support). It only supports 4:2:0 chroma subsampling, while JPEG can handle 4:2:2 and 4:4:4. Google doesn’t seem interested in adding any of these features either.

  But let’s get to the meat and see how these encoders stack up on compressing still images. As I explained in my original analysis, VP8 has the advantage of H.264′s intra prediction, which is one of the primary reasons why H.264 has such an advantage in intra compression. It only has i4x4 and i16x16 modes, not i8x8, so it’s not quite as fancy as H.264′s, but it comes close.

  The test files are all around 155KB ; download them for the exact filesizes. For all three, I did a binary search of quality levels to get the file sizes close. For x264, I encoded with --tune stillimage --preset placebo. For libvpx, I encoded with --best. For JPEG, I encoded with ffmpeg, then applied jpgcrush, a lossless jpeg compressor. I suspect there are better JPEG encoders out there than ffmpeg ; if you have one, feel free to test it and post the results. The source image is the 200th frame of Parkjoy, from derf’s page (fun fact : this video was shot here ! More info on the video here.).

  Files : (x264 [154KB], vp8 [155KB], jpg [156KB])

  Results (decoded to PNG) : (x264, vp8, jpg)

  This seems rather embarrassing for libvpx. Personally I think VP8 looks by far the worst of the bunch, despite JPEG’s blocking. What’s going on here ? VP8 certainly has better entropy coding than JPEG does (by far !). It has better intra prediction (JPEG has just DC prediction). How could VP8 look worse ? Let’s investigate.

  VP8 uses a 4×4 transform, which tends to blur and lose more detail than JPEG’s 8×8 transform. But that alone certainly isn’t enough to create such a dramatic difference. Let’s investigate a hypothesis — that the problem is that libvpx is optimizing for PSNR and ignoring psychovisual considerations when encoding the image… I’ll encode with --tune psnr --preset placebo in x264, turning off all psy optimizations. 

  Files : (x264, optimized for PSNR [154KB]) [Note for the technical people : because adaptive quantization is off, to get the filesize on target I had to use a CQM here.]

  Results (decoded to PNG) : (x264, optimized for PSNR)

  What a blur ! Only somewhat better than VP8, and still worse than JPEG. And that’s using the same encoder and the same level of analysis — the only thing done differently is dropping the psy optimizations. Thus we come back to the conclusion I’ve made over and over on this blog — the encoder matters more than the video format, and good psy optimizations are more important than anything else for compression. libvpx, a much more powerful encoder than ffmpeg’s jpeg encoder, loses because it tries too hard to optimize for PSNR.

  These results raise an obvious question — is Google nuts ? I could understand the push for “WebP” if it was better than JPEG. And sure, technically as a file format it is, and an encoder could be made for it that’s better than JPEG. But note the word “could”. Why announce it now when libvpx is still such an awful encoder ? You’d have to be nuts to try to replace JPEG with this blurry mess as-is. Now, I don’t expect libvpx to be able to compete with x264, the best encoder in the world — but surely it should be able to beat an image format released in 1992 ?

  Earth to Google : make the encoder good first, then promote it as better than the alternatives. The reverse doesn’t work quite as well.

  Addendum (added Oct. 2, 03:51) :

  maikmerten gave me a Theora-encoded image to compare as well. Here’s the PNG and the source (155KB). And yes, that’s Theora 1.2 (Ptalarbvorm) beating VP8 handily. Now that is embarassing. Guess what the main new feature of Ptalarbvorm is ? Psy optimizations…

  Addendum (added Apr. 20, 23:33) :

  There’s a new webp encoder out, written from scratch by skal (available in libwebp). It’s significantly better than libvpx — not like that says much — but it should probably beat JPEG much more readily now. The encoder design is rather unique — it basically uses K-means for a large part of the encoding process. It still loses to x264, but that was expected.

  [155KB]