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• Playing With Emscripten and ASM.js

  1er mars 2014, par Multimedia Mike — General

  The last 5 years or so have provided a tremendous amount of hype about the capabilities of JavaScript. I think it really kicked off when Google announced their Chrome web browser in September, 2008 along with its V8 JS engine. This seemed to spark an arms race in JS engine performance along with much hyperbole that eventually all software could, would, and/or should be written in straight JavaScript for maximum portability and future-proofing, perhaps aided by Emscripten, a tool which magically transforms C and C++ code into JS. The latest round of rhetoric comes courtesy of something called asm.js which purports to narrow the gap between JS and native code performance.

  I haven’t been a believer, to express it charitably. But I wanted to be certain, so I set out to devise my own experiment to test modern JS performance.

  Up Front Summary
  I was extremely surprised that my experiment demonstrated JS performance FAR beyond my expectations. There might be something to these claims of magnficent JS speed in numerical applications. Basically, here were my thoughts during the process :

  • There’s no way that JavaScript can come anywhere close to C performance for a numerically intensive operation ; a simple experiment should demonstrate this.
  • Here’s a straightforward C program to perform a simple yet numerically intensive operation.
  • Let’s compile the C program on gcc and get some baseline performance numbers.
  • Let’s use Emscripten to convert the C program to JavaScript and run it under Chrome.
  • Ha ! Pitiful JS performance, just as I expected !
  • Try the same program under Firefox, since Firefox is supposed to have some crazy optimization for asm.js code, allegedly emitted by Emscripten.
  • LOL ! Firefox performs even worse than Chrome !
  • Wait a minute… the Emscripten documentation mentioned using optimization levels for generating higher performance JS, so try ‘-O1′.
  • Umm… wow : Chrome’s performance increased dramatically ! What about Firefox ? Not only is Firefox faster than Chrome, it’s faster than the gcc-generated code !
  • As my faith in C is suddenly shaken to its core, I remembered to compile the gcc version with an explicit optimization level. The native C version pulled ahead of Firefox again, but the Firefox code is still close.
  • Aha ! This is just desktop– but what about mobile ? One of the leading arguments for converting everything to pure JavaScript is that such programs will magically run perfectly in mobile browsers. So I wager that this is where the experiment will fall over.
  • I proceed to try the same converted program on a variety of mobile platforms.
  • The mobile platforms perform rather admirably as well.
  • I am surprised.

  The Experiment
  I wanted to run a simple yet numerically-intensive and relevant benchmark, and something I am familiar with. I settled on JPEG image decoding. Again, I wanted to keep this simple, ideally in a single file because I didn’t know how hard it might be to deal with Emscripten. I found NanoJPEG, which is a straightforward JPEG decoder contained in a single C file.
  

  I altered nanojpeg.c (to a new file called nanojpeg-static.c) such that the main() program would always load a 1920×1080 (a.k.a. 1080p) JPEG file (“bbb-1080p-title.jpg”, the Big Buck Bunny title), rather than requiring a command line argument. Then I used gettimeofday() to profile the core decoding function (njDecode()).

  Compiling with gcc and profiling execution :

  gcc -Wall nanojpeg-static.c -o nanojpeg-static
  ./nanojpeg-static
  

  Optimization levels such as -O0, -O3, or -Os can be applied to the compilation command.

  For JavaScript conversion, I installed Emscripten and converted using :

  /path/to/emscripten/emcc nanojpeg-static.c -o nanojpeg.html \
    —preload-file bbb-1080p-title.jpg -s TOTAL_MEMORY=32000000
  

  The ‘–preload-file’ option makes the file available to the program via standard C-style file I/O functions. The ‘-s TOTAL_MEMORY’ was necessary because the default of 16 MB wasn’t enough. Again, the -O optimization levels can be sent in.

  For running, the .html file is loaded (via webserver) in a web browser.

  Want To Try It Yourself ?
  I put the files here : http://multimedia.cx/emscripten/. The .c file, the JPEG file, and the Emscripten-converted files using -O0, -O1, -O2, -O3, -Os, and no optimization switch.

  Results and Charts
  Here is the spreadsheet with the raw results.

  I ran this experiment using Ubuntu Linux 12.04 on an Intel Atom N450-based netbook. For this part, I was able to compare the Chrome and Firefox browser results against the C results :

  
  
  

  These are the results for a 2nd generation Android Nexus 7 using both Chrome and Firefox :

  
  
  

  Here is the result for an iPad 2 running iOS 7 and Safari– there is no Firefox for iOS and while there is a version of Chrome for iOS, it apparently isn’t able to leverage an optimized JS engine. Chrome takes so long to complete this experiment that there’s no reason to muddy the graph with the results :
  

  
  
  

  Interesting that -O1 tends to provide better optimization than levels 2 or 3, and that -Os (optimize for size) seems to be a good all-around choice.

  Don’t Get Too Smug
  JavaScript can indeed get amazing performance in this day and age. Please be advised, however, that this isn’t the best that a C decoder implementation can possibly do. This version doesn’t leverage any SIMD extensions. According to profiling (using gprof against the C code), sample saturation in color conversion dominates followed by inverse DCT functions, common cases for SIMD ASM or intrinsics. Allegedly, there will be some support for JS SIMD optimizations some day. We’ll see.

  Implications For Development
  I’m still not especially motivated to try porting the entire Native Client game music player codebase to JavaScript. I’m still wondering about the recommended development flow. How are you supposed to develop for Emscripten and asm.js ? From what I can tell, Emscripten is not designed as a simple aide for porting C/C++ code to JS. No, it reduces the code into JS code you can’t possibly maintain. This seems to imply that the C/C++ code needs to be developed and debugged in its entirety and then converted to JS, which seems arduous.

• How to add black borders to video

  7 décembre 2023, par Arnaud Rochez

  So I'm using ffmpeg to convert a video to 19201080 px, I found two ways to do so, the first one would be to stretch the video to 19201080, but then it looks kinda stretched. I used this command for this :

  


  ./ffmpeg_darwin -i SRC -vf scale=1920:1080,setdar=16:9 DEST


  


  The other option is the same without setdar but this just adapts the resolution to the one it started from (1728*1080).

  


  I would like to fill the 192 pixels of the width with a black border. Is there some kind of option to do so ? Or is there maybe another command line that could achieve this ?

  


• To concatenate more than two video using FFMPEG

  21 décembre 2018, par Alok Kumar Verma

  I’ve been working on FFMPEG, this is indeed not an easy task since I’ve succeeded in doing some work. I’m done with concatenating two videos using ffmpeg but somehow when it comes to more than two it does not work. So I’m finding out some command to do my task.

  The thing I did is to merge two videos are :

  String complexCommand[] = {"-y", "-i", "/mnt/m_external_sd/Videos/VID-20161221-WA0000.mp4", "-i", "/mnt/m_external_sd/Videos/Brodha V - Aathma Raama [Music Video]_HD.mp4", "-strict", "experimental", "-filter_complex",
  
               "[0:v]scale=1920x1080,setsar=1:1[v0];[1:v] scale=iw*min(1920/iw\\,1080/ih):ih*min(1920/iw\\,1080/ih), pad=1920:1080:(1920-iw*min(1920/iw\\,1080/ih))/2:(1080-ih*min(1920/iw\\,1080/ih))/2,setsar=1:1[v1];[v0][0:a][v1][1:a] concat=n=2:v=1:a=1",
  
               "-ab", "48000", "-ac", "2", "-ar", "22050", "-s", "1920x1080", "-vcodec", "libx264","-crf","27","-q","4","-preset", "ultrafast", savingPath};

  The above is working fine for two videos. I’ve tried altering my code for three videos but it does not work.

  What I’ve done in the above code is :

  • Added one more input after the second one
  • Changed the concat=3:v=1:a=1

  But it does not merge and gave me this error in my LogCat :

  FAILED with output : ffmpeg version n3.0.1 Copyright (c) 2000-2016 the FFmpeg developers
  
                                                         built with gcc 4.8 (GCC)
  
                                                         configuration: --target-os=linux --cross-prefix=/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/bin/arm-linux-androideabi- --arch=arm --cpu=cortex-a8 --enable-runtime-cpudetect --sysroot=/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/sysroot --enable-pic --enable-libx264 --enable-libass --enable-libfreetype --enable-libfribidi --enable-libmp3lame --enable-fontconfig --enable-pthreads --disable-debug --disable-ffserver --enable-version3 --enable-hardcoded-tables --disable-ffplay --disable-ffprobe --enable-gpl --enable-yasm --disable-doc --disable-shared --enable-static --pkg-config=/home/vagrant/SourceCode/ffmpeg-android/ffmpeg-pkg-config --prefix=/home/vagrant/SourceCode/ffmpeg-android/build/armeabi-v7a --extra-cflags='-I/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/include -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fno-strict-overflow -fstack-protector-all' --extra-ldflags='-L/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/lib -Wl,-z,relro -Wl,-z,now -pie' --extra-libs='-lpng -lexpat -lm' --extra-cxxflags=
  
                                                         libavutil      55. 17.103 / 55. 17.103
  
                                                         libavcodec     57. 24.102 / 57. 24.102
  
                                                         libavformat    57. 25.100 / 57. 25.100
  
                                                         libavdevice    57.  0.101 / 57.  0.101
  
                                                         libavfilter     6. 31.100 /  6. 31.100
  
                                                         libswscale      4.  0.100 /  4.  0.100
  
                                                         libswresample   2.  0.101 /  2.  0.101
  
                                                         libpostproc    54.  0.100 / 54.  0.100
  
                                                       Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/mnt/m_external_sd/Videos/VID-20161221-WA0000.mp4':
  
                                                         Metadata:
  
                                                           major_brand     : isom
  
                                                           minor_version   : 512
  
                                                           compatible_brands: isomiso2avc1mp41
  
                                                           encoder         : Lavf57.25.100
  
                                                         Duration: 00:02:47.09, start: 0.000000, bitrate: 245 kb/s
  
                                                           Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 854x480 [SAR 1:1 DAR 427:240], 112 kb/s, 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc (default)
  
                                                           Metadata:
  
                                                             handler_name    : VideoHandler
  
                                                           Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
  
                                                           Metadata:
  
                                                             handler_name    : SoundHandler
  
                                                       Input #1, mov,mp4,m4a,3gp,3g2,mj2, from '/mnt/m_external_sd/Videos/Brodha V - Aathma Raama [Music Video]_HD.mp4':
  
                                                         Metadata:
  
                                                           major_brand     : mp42
  
                                                           minor_version   : 0
  
                                                           compatible_brands: isommp42
  
                                                           creation_time   : 2013-12-15 13:11:41
  
                                                         Duration: 00:03:51.08, start: 0.000000, bitrate: 1693 kb/s
  
                                                           Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720, 1498 kb/s, 25 fps, 25 tbr, 50 tbn, 50 tbc (default)
  
                                                           Metadata:
  
                                                             handler_name    : VideoHandler
  
                                                           Stream #1:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 191 kb/s (default)
  
                                                           Metadata:
  
                                                             creation_time   : 2013-12-15 13:11:41
  
                                                             handler_name    : IsoMedia File Produced by Google, 5-11-2011
  
                                                       Input #2, mov,mp4,m4a,3gp,3g2,mj2, from '/mnt/m_external_sd/DCIM/Sinha's POP/20150530_073113.mp4':
  
                                                         Metadata:
  
                                                           major_brand     : isom
  
                                                           minor_version   : 0
  
                                                           compatible_brands: isom3gp4
  
                                                           creation_time   : 2015-05-30 02:06:06
  
                                                         Duration: 00:04:48.48, start: 0.000000, bitrate: 3608 kb/s
  
                                                           Stream #2:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 720x480, 3478 kb/s, 30.28 fps, 30 tbr, 90k tbn, 180k tbc (default)
  
                                                           Metadata:
  
                                                             creation_time   : 2015-05-30 02:06:06
  
                                                             handler_name    : VideoHandle
  
                                                             encoder         :                                
  
                                                           Stream #2:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 125 kb/s (default)
  
                                                           Metadata:
  
                                                             creation_time   : 2015-05-30 02:06:06
  
                                                             handler_name    : SoundHandle
  
                                                       [Parsed_setsar_1 @ 0xa9ea9220] num:den syntax is deprecated, please use num/den or named options instead
  
                                                       [Parsed_setsar_4 @ 0xa9ea9310] num:den syntax is deprecated, please use num/den or named options instead
  
                                                       [Parsed_setsar_1 @ 0xa9ea92c0] num:den syntax is deprecated, please use num/den or named options instead
  
                                                       [Parsed_setsar_4 @ 0xa9ea93b0] num:den syntax is deprecated, please us

  I’ve tried one more command which works fine for concatenating two videos but still it does not work for more than two videos :

  String complexCommand[] = {"-y", "-i", "/mnt/m_external_sd/Videos/VID-20161221-WA0000.mp4", "-i", "/mnt/m_external_sd/Videos/Brodha V - Aathma Raama [Music Video]_HD.mp4", "-i", "/mnt/m_external_sd/DCIM/Sinha's POP/20150530_073113.mp4", "-strict", "experimental", "-filter_complex",
  
              "[0:v]scale=480x640,setsar=1:1[v0];[1:v]scale=480x640,setsar=1:1[v1];[v0][0:a][v1][1:a] concat=n=3:v=1:a=1",
  
              "-ab", "48000", "-ac", "2", "-ar", "22050", "-s", "480x640", "-vcodec", "libx264","-crf","27","-q","4","-preset", "ultrafast", savingPath};

  You can clearly see in the above code that I’ve tried using this for the three videos but still no luck. Will appreciate your help. Thanks.

  EDITS

  After following the LordNeckbeard’s suggestion from the comment section, I’ve used his suggestion in my code but after doing that still no luck however the console’s output got changed and here is the command which I used :

  String complexCommand[] = {"-y", "-i", "/mnt/m_external_sd/Videos/VID-20161221-WA0000.mp4", "-i", "/mnt/m_external_sd/Videos/Brodha V - Aathma Raama [Music Video]_HD.mp4", "-i", "/mnt/m_external_sd/DCIM/Sinha's POP/20150530_073113.mp4", "-strict", "experimental", "-filter_complex",
  
              "[0:v]scale=480x640,setsar=1[v0];[1:v]scale=480x640,setsar=1[v1];[v0][0:a][v1][1:a] concat=n=3:v=1:a=1",
  
              "-ab", "48000", "-ac", "2", "-ar", "22050", "-s", "480x640", "-vcodec", "libx264","-crf","27","-preset", "ultrafast", savingPath};

  Here you can clearly see that I’ve used setsar=1 and used -crf only.

  And the logs are :

  FAILED with output : ffmpeg version n3.0.1 Copyright (c) 2000-2016 the FFmpeg developers
  
                                                           built with gcc 4.8 (GCC)
  
                                                           configuration: --target-os=linux --cross-prefix=/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/bin/arm-linux-androideabi- --arch=arm --cpu=cortex-a8 --enable-runtime-cpudetect --sysroot=/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/sysroot --enable-pic --enable-libx264 --enable-libass --enable-libfreetype --enable-libfribidi --enable-libmp3lame --enable-fontconfig --enable-pthreads --disable-debug --disable-ffserver --enable-version3 --enable-hardcoded-tables --disable-ffplay --disable-ffprobe --enable-gpl --enable-yasm --disable-doc --disable-shared --enable-static --pkg-config=/home/vagrant/SourceCode/ffmpeg-android/ffmpeg-pkg-config --prefix=/home/vagrant/SourceCode/ffmpeg-android/build/armeabi-v7a --extra-cflags='-I/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/include -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fno-strict-overflow -fstack-protector-all' --extra-ldflags='-L/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/lib -Wl,-z,relro -Wl,-z,now -pie' --extra-libs='-lpng -lexpat -lm' --extra-cxxflags=
  
                                                           libavutil      55. 17.103 / 55. 17.103
  
                                                           libavcodec     57. 24.102 / 57. 24.102
  
                                                           libavformat    57. 25.100 / 57. 25.100
  
                                                           libavdevice    57.  0.101 / 57.  0.101
  
                                                           libavfilter     6. 31.100 /  6. 31.100
  
                                                           libswscale      4.  0.100 /  4.  0.100
  
                                                           libswresample   2.  0.101 /  2.  0.101
  
                                                           libpostproc    54.  0.100 / 54.  0.100
  
                                                         Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/mnt/m_external_sd/Videos/VID-20161221-WA0000.mp4':
  
                                                           Metadata:
  
                                                             major_brand     : isom
  
                                                             minor_version   : 512
  
                                                             compatible_brands: isomiso2avc1mp41
  
                                                             encoder         : Lavf57.25.100
  
                                                           Duration: 00:02:47.09, start: 0.000000, bitrate: 245 kb/s
  
                                                             Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 854x480 [SAR 1:1 DAR 427:240], 112 kb/s, 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc (default)
  
                                                             Metadata:
  
                                                               handler_name    : VideoHandler
  
                                                             Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
  
                                                             Metadata:
  
                                                               handler_name    : SoundHandler
  
                                                         Input #1, mov,mp4,m4a,3gp,3g2,mj2, from '/mnt/m_external_sd/Videos/Brodha V - Aathma Raama [Music Video]_HD.mp4':
  
                                                           Metadata:
  
                                                             major_brand     : mp42
  
                                                             minor_version   : 0
  
                                                             compatible_brands: isommp42
  
                                                             creation_time   : 2013-12-15 13:11:41
  
                                                           Duration: 00:03:51.08, start: 0.000000, bitrate: 1693 kb/s
  
                                                             Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720, 1498 kb/s, 25 fps, 25 tbr, 50 tbn, 50 tbc (default)
  
                                                             Metadata:
  
                                                               handler_name    : VideoHandler
  
                                                             Stream #1:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 191 kb/s (default)
  
                                                             Metadata:
  
                                                               creation_time   : 2013-12-15 13:11:41
  
                                                               handler_name    : IsoMedia File Produced by Google, 5-11-2011
  
                                                         Input #2, mov,mp4,m4a,3gp,3g2,mj2, from '/mnt/m_external_sd/DCIM/Sinha's POP/20150530_073113.mp4':
  
                                                           Metadata:
  
                                                             major_brand     : isom
  
                                                             minor_version   : 0
  
                                                             compatible_brands: isom3gp4
  
                                                             creation_time   : 2015-05-30 02:06:06
  
                                                           Duration: 00:04:48.48, start: 0.000000, bitrate: 3608 kb/s
  
                                                             Stream #2:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 720x480, 3478 kb/s, 30.28 fps, 30 tbr, 90k tbn, 180k tbc (default)
  
                                                             Metadata:
  
                                                               creation_time   : 2015-05-30 02:06:06
  
                                                               handler_name    : VideoHandle
  
                                                               encoder         :                                
  
                                                             Stream #2:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 125 kb/s (default)
  
                                                             Metadata:
  
                                                               creation_time   : 2015-05-30 02:06:06
  
                                                               handler_name    : SoundHandle
  
                                                         [Parsed_concat_4 @ 0xa7ea91d0] Input link in2:v0 parameters (size 720x480, SAR 0:1) do not match the corresponding output link in0:v0 parameters (480x640, SAR 1:1)
  
                                                         [Parsed_concat_4 @ 0xa7ea91d0] Failed to configure output pad on Parsed_concat_4
  
                                                         Error configuring complex filters.
  
                                                         Invalid argument

  NOTE : I have tried using setsar=1/1 but still got the same result.