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• 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]

• Launch Leech and the History of WMV

  14 septembre 2010, par Multimedia Mike — General

  I was combing through my programming archives again and came across an old Perl script called launch-leech.pl. This was a private script I used to maintain for the benefit of myself and a few friends. See, there was this site called Launch.com (URL doesn’t seem to do anything as of this writing but here’s the Wikipedia page). Purchased by Yahoo ! in 2001, Launch still maintained their independent branding. They also carried a lot of music videos, of which I am a huge junkie. launch-leech.pl was the tool I used to download the videos. This was particularly useful since I stubbornly clung to dialup internet access until mid-2004 and it would have been impossible to stream video at any decent quality (though there were 56k streams, so like I said– not possible at any decent quality).

  
  
  

  Technically
  I followed Launch.com for many years. To be honest, I only “followed” in that I figured out where their “latest videos” URL lived and regularly polled it. Each video had either a 6-, 7-, or 8-digit unique ID that could be plugged into the launch-leech.pl script which would then have a conversation with the relevant servers, determine the correct streaming URL with the highest quality, then download and save the URL by handing it off to an external program (first ASFRecorder, though I later switched to mmsclient).

  At one point, I even wrote a crawler that compiled an offline database of all the videos, their IDs and their metadata. I never thought of anything interesting to do with it, though.

  
  
  

  Windows Media Legacy
  During these glory days of leeching, Launch.com streamed using Windows Media. I admit, it’s a bit of a blur now — the site might have used Real or QuickTime, but I was obviously most in tune with the WM side. I remember when I first found the site circa 2000-2001, the videos were in MS MPEG-4v3, and the high quality bitrate was 300 kbits/sec. Eventually, Launch.com would stream WMV7, WMV8, and finally WMV9, with bitrates up to 700 kbits/sec. However, they never broke free of the 320×240 encoding resolution, which was frustrating. When I wasn’t able to notice any substantial difference between 300 and 700 kbits/sec, I felt it might be time to put those extra bits to work on a resolution upgrade.

  At least they were nice enough to re-encode a number of old videos using better codecs and bitrates with each revision, thus prompting me to scan through the site collecting updated video IDs for download.

  
  
  

  Epilogue
  I don’t clearly remember when I stopped visiting Launch.com. Video-wise, the web has been a blur of Flash video ever since about 2006. Meanwhile, I spent a lot of time collecting a bunch of music videos in the first half of the decade only to find that pretty much every version of every music video made since the dawn of time is available on demand thanks to YouTube. I have found that this phenomenon manifests in many areas as internet technology marches on.

  The Real Entertainment
  The launch-leech.pl tool represents a recurring pattern for me. I derive as much — if not more — entertainment from creating programs like launch-leech.pl (and implicitly reverse engineering something in the process ; in this case, a website) as I do from the intended entertainment media itself. I seem to have this issue a lot with games, too.

  Is this an issue for anyone else ? Am I the only one who would rather play with the box that a shiny toy comes packaged in ?

• FFMpeg and WebM/VP8

  25 novembre 2011, par Anand Suresh

  I am trying to use ffmpeg and ffserver to stream VP8 video.

  I am using the following command to start FFMpeg :

  ffmpeg -v 9 -loglevel 99 -f x11grab -s 1440x900 -r2 -i :0.0 -f webm http://localhost:8090/feed1.ffm

  The above command abruptly terminates generating the following error :

  > FFmpeg version 0.6.2-4:0.6.2-1ubuntu1.1, Copyright (c) 2000-2010 the Libav developers
  
    built on Sep 16 2011 16:57:46 with gcc 4.5.2
  
    configuration: --extra-version=4:0.6.2-1ubuntu1.1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --enable-libvpx --disable-stripping --enable-runtime-cpudetect --enable-vaapi --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --enable-shared --disable-static
  
    WARNING: library configuration mismatch
  
    libavutil   configuration: --extra-version=4:0.6.2-1ubuntu1.1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --enable-libvpx --disable-stripping --enable-runtime-cpudetect --enable-vaapi --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --shlibdir=/usr/lib/i686/cmov --cpu=i686 --enable-shared --disable-static --disable-ffmpeg --disable-ffplay
  
    libavcodec  configuration: --extra-version=4:0.6.2-1ubuntu1.1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --enable-libvpx --disable-stripping --enable-runtime-cpudetect --enable-vaapi --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --shlibdir=/usr/lib/i686/cmov --cpu=i686 --enable-shared --disable-static --disable-ffmpeg --disable-ffplay
  
    libavformat configuration: --extra-version=4:0.6.2-1ubuntu1.1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --enable-libvpx --disable-stripping --enable-runtime-cpudetect --enable-vaapi --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --shlibdir=/usr/lib/i686/cmov --cpu=i686 --enable-shared --disable-static --disable-ffmpeg --disable-ffplay
  
    libavdevice configuration: --extra-version=4:0.6.2-1ubuntu1.1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --enable-libvpx --disable-stripping --enable-runtime-cpudetect --enable-vaapi --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --shlibdir=/usr/lib/i686/cmov --cpu=i686 --enable-shared --disable-static --disable-ffmpeg --disable-ffplay
  
    libavfilter configuration: --extra-version=4:0.6.2-1ubuntu1.1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --enable-libvpx --disable-stripping --enable-runtime-cpudetect --enable-vaapi --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --shlibdir=/usr/lib/i686/cmov --cpu=i686 --enable-shared --disable-static --disable-ffmpeg --disable-ffplay
  
    libswscale  configuration: --extra-version=4:0.6.2-1ubuntu1.1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --enable-libvpx --disable-stripping --enable-runtime-cpudetect --enable-vaapi --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --shlibdir=/usr/lib/i686/cmov --cpu=i686 --enable-shared --disable-static --disable-ffmpeg --disable-ffplay
  
    libpostproc configuration: --extra-version=4:0.6.2-1ubuntu1.1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --enable-libvpx --disable-stripping --enable-runtime-cpudetect --enable-vaapi --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --shlibdir=/usr/lib/i686/cmov --cpu=i686 --enable-shared --disable-static --disable-ffmpeg --disable-ffplay
  
    libavutil     50.15. 1 / 50.15. 1
  
    libavcodec    52.72. 2 / 52.72. 2
  
    libavformat   52.64. 2 / 52.64. 2
  
    libavdevice   52. 2. 0 / 52. 2. 0
  
    libavfilter    1.19. 0 /  1.19. 0
  
    libswscale     0.11. 0 /  0.11. 0
  
    libpostproc   51. 2. 0 / 51. 2. 0
  
  [x11grab @ 0x9869420]device: :0.0 -> display: :0.0 x: 0 y: 0 width: 1440 height: 900
  
  [x11grab @ 0x9869420]shared memory extension  found
  
  [x11grab @ 0x9869420]Probe buffer size limit 5000000 reached
  
  [x11grab @ 0x9869420]Estimating duration from bitrate, this may be inaccurate
  
  Input #0, x11grab, from ':0.0':
  
    Duration: N/A, start: 1322253753.374957, bitrate: 41472 kb/s
  
      Stream #0.0, 1, 1/1000000: Video: rawvideo, bgra, 1440x900, 1/1, 41472 kb/s, 1 tbr, 1000k tbn, 1 tbc
  
  [libvpx @ 0x9876540]v0.9.6
  
  [libvpx @ 0x9876540]--enable-pic --enable-shared --disable-install-bins --disable-install-srcs --target=x86-linux-gcc
  
  [libvpx @ 0x9876540]vpx_codec_enc_cfg
  
  [libvpx @ 0x9876540]generic settings
  
    g_usage:                      0
  
    g_threads:                    0
  
    g_profile:                    0
  
    g_w:                          320
  
    g_h:                          240
  
    g_timebase:                   {1/30}
  
    g_error_resilient:            0
  
    g_pass:                       0
  
    g_lag_in_frames:              0
  
  [libvpx @ 0x9876540]rate control settings
  
    rc_dropframe_thresh:          0
  
    rc_resize_allowed:            0
  
    rc_resize_up_thresh:          60
  
    rc_resize_down_thresh:        30
  
    rc_end_usage:                 0
  
    rc_twopass_stats_in:          (nil)(0)
  
    rc_target_bitrate:            256
  
  [libvpx @ 0x9876540]quantizer settings
  
    rc_min_quantizer:             4
  
    rc_max_quantizer:             63
  
  [libvpx @ 0x9876540]bitrate tolerance
  
    rc_undershoot_pct:            95
  
    rc_overshoot_pct:             200
  
  [libvpx @ 0x9876540]decoder buffer model
  
    rc_buf_sz:                    6000
  
    rc_buf_initial_sz:            4000
  
    rc_buf_optimal_sz:            5000
  
  [libvpx @ 0x9876540]2 pass rate control settings
  
    rc_2pass_vbr_bias_pct:        50
  
    rc_2pass_vbr_minsection_pct:  0
  
    rc_2pass_vbr_maxsection_pct:  400
  
  [libvpx @ 0x9876540]keyframing settings
  
    kf_mode:                      1
  
    kf_min_dist:                  0
  
    kf_max_dist:                  9999
  
  [libvpx @ 0x9876540]
  
  [libvpx @ 0x9876540]vpx_codec_enc_cfg
  
  [libvpx @ 0x9876540]generic settings
  
    g_usage:                      0
  
    g_threads:                    1
  
    g_profile:                    0
  
    g_w:                          1440
  
    g_h:                          900
  
    g_timebase:                   {1/1}
  
    g_error_resilient:            0
  
    g_pass:                       0
  
    g_lag_in_frames:              0
  
  [libvpx @ 0x9876540]rate control settings
  
    rc_dropframe_thresh:          0
  
    rc_resize_allowed:            0
  
    rc_resize_up_thresh:          60
  
    rc_resize_down_thresh:        30
  
    rc_end_usage:                 0
  
    rc_twopass_stats_in:          (nil)(0)
  
    rc_target_bitrate:            200
  
  [libvpx @ 0x9876540]quantizer settings
  
    rc_min_quantizer:             1
  
    rc_max_quantizer:             38
  
  [libvpx @ 0x9876540]bitrate tolerance
  
    rc_undershoot_pct:            95
  
    rc_overshoot_pct:             200
  
  [libvpx @ 0x9876540]decoder buffer model
  
    rc_buf_sz:                    6000
  
    rc_buf_initial_sz:            4000
  
    rc_buf_optimal_sz:            5000
  
  [libvpx @ 0x9876540]2 pass rate control settings
  
    rc_2pass_vbr_bias_pct:        50
  
    rc_2pass_vbr_minsection_pct:  0
  
    rc_2pass_vbr_maxsection_pct:  400
  
  [libvpx @ 0x9876540]keyframing settings
  
    kf_mode:                      1
  
    kf_min_dist:                  0
  
    kf_max_dist:                  12
  
  [libvpx @ 0x9876540]
  
  [libvpx @ 0x9876540]vpx_codec_control
  
  [libvpx @ 0x9876540]  VP8E_SET_CPUUSED:             3
  
  [libvpx @ 0x9876540]  VP8E_SET_NOISE_SENSITIVITY:   0
  
  Output #0, webm, to 'http://127.0.0.1:8090/feed1.ffm':
  
    Metadata:
  
      encoder         : Lavf52.64.2
  
      Stream #0.0, 0, 1/1000: Video: libvpx, yuv420p, 1440x900, 1/1, q=2-31, 200 kb/s, 1k tbn, 1 tbc
  
  Stream mapping:
  
    Stream #0.0 -> #0.0
  
  Press [q] to stop encoding
  
  [webm @ 0x98753b0]Writing block at offset 15, size 158658, pts 0, dts 0, duration 1000, flags 128
  
  [webm @ 0x98753b0]Starting new cluster at offset 158681 bytes, pts 0

  Can anyone point out what I am doing wrong here ? Why does ffmpeg die everytime it starts a new cluster ?

  Thanks