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• Curator of the Samples Archive

  13 mai 2011, par Multimedia Mike — General

  Remember how I mirrored the world-famous MPlayerHQ samples archive a few months ago ? Due to a series of events, the original archive is no longer online. However, me and the people who control the mplayerhq.hu domain figured out how to make samples.mplayerhq.hu point to samples.multimedia.cx.

  That means... I’m the current owner and curator of our central multimedia samples repository. Such power ! This should probably be the fulfillment of a decade-long dream for me, having managed swaths of the archive, most notably the game formats section.

  How This Came To Be

  If you pay any attention to the open source multimedia scene, you might have noticed that there has been a smidge of turmoil. Heated words were exchanged, authority was questioned, some people probably said some things they didn’t mean, and the upshot is that, where once there was one project (FFmpeg), there are now 2 projects (also Libav). And to everyone who has wanted me to mention it on my blog— there, I finally broke my silence and formally acknowledged the schism.

  For my part, I was just determined to ensure that the samples archive remained online, preferably at the original samples.mplayerhq.hu address. There are 10 years worth of web links out there pointing into the original repository.

  Better Solution

  I concede that it’s not entirely optimal to host the repository here at multimedia.cx. While I can offer a crazy amount of monthly bandwidth, I can’t offer rsync (invaluable for keeping mirrors in sync), nor can the server provide anonymous FTP or allow me to offer accounts to other admins who can manage the repository.

  The samples archive is also mirrored at samples.libav.org/samples. I understand that service is provided by VideoLAN. Right now, both repositories are known to be static. I’m open to brainstorms about how to improve the situation.

• Programming Language Levels

  20 mai 2011, par Multimedia Mike — Programming

  I’ve been doing this programming thing for some 20 years now. Things sure do change. One change I ponder from time to time is the matter of programming language levels. Allow me to explain.

  The 1990s
  When I first took computer classes in the early 1990s, my texts would classify computer languages into 3 categories, or levels. The lower the level, the closer to the hardware ; the higher the level, the more abstract (and presumably, easier to use). I recall that the levels went something like this :

  • High level : Pascal, BASIC, Logo, Fortran
  • Medium level : C, Forth
  • Low level : Assembly language

  Keep in mind that these were the same texts which took the time to explain the history of computers from mainframes -> minicomputers -> a relatively recent phenomenon called microcomputers or "PCs".

  Somewhere in the mid-late 1990s, when I was at university, I was introduced to a new tier :

  • Very high level : Perl, shell scripting

  I think there was some debate among my peers about whether C++ and Java were properly classified as high or very high level. The distinction between high and very high, in my observation, seemed to be that very high level languages had more complex data structures (at the very least, a hash / dictionary / associative array / key-value map) built into the language, as well as implicit memory management.

  Modern Day
  These days, the old hierarchy is apparently forgotten (much like minicomputers). I observe that there is generally a much simpler 2-tier classification :

  • Low level : C, assembly language
  • High level : absolutely every other programming language in wide use today

  I find myself wondering where C++ and Objective-C fit in this classification scheme. Then I remember that it doesn’t matter and this is all academic.

  Relevancy
  I think about this because I have pretty much stuck to low-level programming all of my life, mostly due to my interest in game and multimedia-type programming. But the trends in computing have favored many higher level languages and programming paradigms. I woke up one day and realized that the kind of work I often do — lower level stuff — is not very common.

  I’m not here to argue that low or high level is superior. You know I’m all about using the appropriate tool for the job. But I sometimes find myself caught between worlds, having the defend and explain one to the other.

  • On one hand, it’s not unusual for the multitudes of programmers working at the high level to gasp and wonder why I or anyone else would ever use C or assembly language for anything when there are so many beautiful high level languages. I patiently explain that those languages have to be written in some other language (at first) and that they need to run on some operating system and that most assuredly won’t be written in a high level language. For further reading, I refer them to Joel Spolsky’s great essay called Back to Basics which describes why it can be useful to know at least a little bit about how the computer does what it does at the lowest levels.
  • On the other hand, believe it or not, I sometimes have to defend the merits of high level languages to my low level brethren. I’ll often hear variations of, "Any program can be written in C. Using a high level language to achieve the same will create a slow and bloated solution." I try to explain that the trade-off in time to complete the programming task weighed against the often-negligible performance hit of what is often an I/O-bound operation in the first place makes it worthwhile to use the high level language for a wide variety of tasks.

    Or I just ignore them. That’s actually the best strategy.

• Improve ffmpeg x11grab screen capture performance

  10 janvier 2020, par Toby Eggitt

  I have been doing screen-only (no sound) capture using ffmpeg with libx264 for the encoding quite successfully on an old machine built around a Core2 Quad Q6600 processor. I now need to include audio in this, but the fans on this ancient machine are too loud. So, I found a fanless motherboard (https://www.asrock.com/mb/Intel/J5005-ITX/index.asp) that has an Intel Pentium Silver J5005 processor and decided to use this instead. The CPU’s benchmarks put it in a similar bracket to the Q6600, and the general performance seems to be significantly better, presumably at least in part because it’s now using DDR4 memory that’s faster access.

  However, the machine fails horribly at the screen capture. It’s missing frames all over the place ; I actually end up with video that’s missing almost half the frames, and plays back at about double speed. Also, any audio is just messed up so badly I can hardly think how to describe it, best I can come up with is that I get perhaps a quarter second of sound then a few seconds pause (the video meanwhile is actually still playing back, albeit with no sense of time).

  Some things occur to me that might be the cause, or cure, of my troubles, some of which I might be able to fix, others not so much. What other things should I try ? (I’d prefer to avoid simply throwing money at the issue with random ideas that are baseless !)

  1) perhaps the CPU lacks some "extensions" to the instruction set (I recall years ago some CPUs gaining MMX extensions") so that the CPU is fast at mundane computing but sucks at video encoding.

  2) perhaps the fact that the old machine had a dedicated graphics card, while this new one is sharing main memory with the graphics system means that reading the screen pixels is much slower.

  3) perhaps the fact that this new machine has a single DDR4 memory stick in it means that I’m forcing all the memory reads and writes for the computations through the same memory as is holding the screen, and that’s too much (implying that adding an additional memory stick might jus possibly help ?)

  4) perhaps there’s some bios setting that would allow more efficient sharing of video memory ?

  5) my favorite, perhaps there’s a better compression library that I could use to get decent quality screen capture with much less CPU usage.

  I should also note that I have tried this with -threads 0, and the CPU usage hovers between 100% and 200% ; around 100% when the screen is static, and rising as I move windows around and otherwise create more output.

  6) the motherboard claims to have some kind of hardware video encoder built into it. I haven’t paid this any attention to this point, as I assumed it was for the purpose of taking HDMI input and encoding it, but maybe there’s a way to use this, if so, what libraries might I need to get ffmpeg to do this.

  Edits :

  • This is an off the shelf ffmpeg. I’m certainly willing to try building it myself if I have some idea what I should do different.
  • The motherboard claims to have hardware encoders, but I’m struggling to find out what they are (seems like it’s an Intel chip called "UHD Graphics 605" but nothing I can find suggests ffmpeg can work with that)

  • command line right now has been (without audio) :

    ffmpeg  -video_size 1280x720   -f x11grab  -i ${DISPLAY}+100,100  -vcodec libx264  -f alsa -i pulse -acodec ac3 -threads 0  ./video$(date +%F-%H-%M-%S).mp4

  Log from a short recording session is :

  ffmpeg version 3.4.6-0ubuntu0.18.04.1 Copyright (c) 2000-2019 the FFmpeg developers
  
    built with gcc 7 (Ubuntu 7.3.0-16ubuntu3)
  
    configuration: --prefix=/usr --extra-version=0ubuntu0.18.04.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --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-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --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-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  
    libavutil      55. 78.100 / 55. 78.100
  
    libavcodec     57.107.100 / 57.107.100
  
    libavformat    57. 83.100 / 57. 83.100
  
    libavdevice    57. 10.100 / 57. 10.100
  
    libavfilter     6.107.100 /  6.107.100
  
    libavresample   3.  7.  0 /  3.  7.  0
  
    libswscale      4.  8.100 /  4.  8.100
  
    libswresample   2.  9.100 /  2.  9.100
  
    libpostproc    54.  7.100 / 54.  7.100
  
  [x11grab @ 0x561a723e5ac0] Stream #0: not enough frames to estimate rate; consider increasing probesize
  
  Input #0, x11grab, from ':0+100,100':
  
    Duration: N/A, start: 1578693116.465807, bitrate: N/A
  
      Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1280x720, 29.97 fps, 1000k tbr, 1000k tbn, 1000k tbc
  
  Unknown decoder 'libx264'
  
  simon@studio:~$ ffmpeg  -video_size 1280x720   -f x11grab  -i ${DISPLAY}+100,100  -vcodec libx264 -threads 0  ./video$(date +%F-%H-%M-%S).mp4
  
  ffmpeg version 3.4.6-0ubuntu0.18.04.1 Copyright (c) 2000-2019 the FFmpeg developers
  
    built with gcc 7 (Ubuntu 7.3.0-16ubuntu3)
  
    configuration: --prefix=/usr --extra-version=0ubuntu0.18.04.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --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-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --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-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  
    libavutil      55. 78.100 / 55. 78.100
  
    libavcodec     57.107.100 / 57.107.100
  
    libavformat    57. 83.100 / 57. 83.100
  
    libavdevice    57. 10.100 / 57. 10.100
  
    libavfilter     6.107.100 /  6.107.100
  
    libavresample   3.  7.  0 /  3.  7.  0
  
    libswscale      4.  8.100 /  4.  8.100
  
    libswresample   2.  9.100 /  2.  9.100
  
    libpostproc    54.  7.100 / 54.  7.100
  
  [x11grab @ 0x558225bc29a0] Stream #0: not enough frames to estimate rate; consider increasing probesize
  
  Input #0, x11grab, from ':0+100,100':
  
    Duration: N/A, start: 1578693132.513351, bitrate: N/A
  
      Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1280x720, 29.97 fps, 1000k tbr, 1000k tbn, 1000k tbc
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
  
  Press [q] to stop, [?] for help
  
  [libx264 @ 0x558225bcd360] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
  
  [libx264 @ 0x558225bcd360] profile High 4:4:4 Predictive, level 3.1, 4:4:4 8-bit
  
  [libx264 @ 0x558225bcd360] 264 - core 152 r2854 e9a5903 - H.264/MPEG-4 AVC codec - Copyleft 2003-2017 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x1:0x111 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=4 threads=6 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
  
  Output #0, mp4, to './video2020-01-10-14-52-12.mp4':
  
    Metadata:
  
      encoder         : Lavf57.83.100
  
      Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv444p, 1280x720, q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
  
      Metadata:
  
        encoder         : Lavc57.107.100 libx264
  
      Side data:
  
        cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
  
  Past duration 0.806847 too large     256kB time=00:00:00.43 bitrate=4835.3kbits/s dup=16 drop=0 speed=0.207x    
  
  frame=  371 fps= 29 q=-1.0 Lsize=     639kB time=00:00:12.27 bitrate= 426.6kbits/s dup=16 drop=14 speed=0.971x    
  
  video:634kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.813096%
  
  [libx264 @ 0x558225bcd360] frame I:2     Avg QP:18.16  size:221502
  
  [libx264 @ 0x558225bcd360] frame P:93    Avg QP:14.97  size:  2007
  
  [libx264 @ 0x558225bcd360] frame B:276   Avg QP:20.13  size:    69
  
  [libx264 @ 0x558225bcd360] consecutive B-frames:  0.8%  0.0%  0.0% 99.2%
  
  [libx264 @ 0x558225bcd360] mb I  I16..4: 44.6%  0.0% 55.4%
  
  [libx264 @ 0x558225bcd360] mb P  I16..4:  0.2%  0.0%  0.3%  P16..4:  0.7%  0.1%  0.1%  0.0%  0.0%    skip:98.5%
  
  [libx264 @ 0x558225bcd360] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8:  1.0%  0.0%  0.0%  direct: 0.0%  skip:99.0%  L0:50.9% L1:49.0% BI: 0.1%
  
  [libx264 @ 0x558225bcd360] coded y,u,v intra: 41.3% 37.5% 37.4% inter: 0.1% 0.0% 0.0%
  
  [libx264 @ 0x558225bcd360] i16 v,h,dc,p: 58% 41%  1%  0%
  
  [libx264 @ 0x558225bcd360] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 33% 30% 14%  2%  4%  4%  5%  3%  5%
  
  [libx264 @ 0x558225bcd360] Weighted P-Frames: Y:0.0% UV:0.0%
  
  [libx264 @ 0x558225bcd360] ref P L0: 59.2%  8.8% 25.5%  6.5%
  
  [libx264 @ 0x558225bcd360] ref B L0: 59.4% 39.0%  1.6%
  
  [libx264 @ 0x558225bcd360] ref B L1: 96.5%  3.5%
  
  [libx264 @ 0x558225bcd360] kb/s:419.29
  
  Exiting normally, received signal 2.