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• Best way to go about video playback for WebAssembly, Linux, Windows, and Android

  13 janvier 2021, par Michael Macha

  I'm currently working on a game as a passtime during quarantine. It currently builds, via a Makefile, for WASM, Linux, and Windows ; and is eventually planned to be ported to Android through NDK. The API used is (primarily) SDL, with SDL Image and SDL Mixer, and all graphics go through OpenGL.

  


  As of the moment, all graphics, sound, and control is running perfectly ; but I would like to add video cut scenes and I'm uncertain of how to do this with WASM. I recognize that maybe half of the system resources are available in a browser, and am willing to drop fidelity in the web version to compensate. Currently, all code is in C and GLSL ; but if I need to I can add C++, or a little extra JavaScript.

  


  My compilers, for each platform, are gcc, emcc, and mingw32. They're all called through Maketools. As of the moment, it looks like I can just use FFMPEG for gcc & mingw ; but what's best for emcc, which does not have an FFMPEG port available ? Will I need to call something else, or use some specific browser function ? What is the simplest way to go about this, and does anyone have a basic tutorial for in-browser video with WebAssembly ?

  


  For a little further data, I'm debuting my project on Itch.io. For a launched-in-browser game, they require a zip file with an HTML file called index.html, and any support files, within it. (Total file size is effectively limited to 1 GB.) I'm expecting a minimum of 640x480 resolution, but would prefer higher. I'm currently digging through online examples but haven't yet found anything sufficiently basic. (This might change as I keep digging, and I'll update the question if I find anything.)

  


• Trying to understand the ffmpeg seek cut functionality

  13 février 2020, par user3841429

  I have a video where I would like to cut a part from. The command I use :

  ffmpeg -ss 526.623 -t 347.986 -i 'example.mp4' -c copy -avoid_negative_ts 1 -y res.mp4

  Where expected length is 00:05:47.99. The process log shows the following :

  ...
  
  frame=10582 fps=8258 q=-1.0 Lsize= 1061446kB time=00:05:47.98 bitrate=24987.8kbits/s speed= 272x    
  
  video:1044531kB audio:16556kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.033789%

  As you can see time=00:05:47.98 as expected, but when I play this video in player I see that it has extra 5 seconds of video at the end. I check the playtime length :

  $ ffmpeg -i 'res.mp4' 2>&1 | grep Duration | cut -d ' ' -f 4 | sed s/,//
  
  00:05:53.11

  What the... My clue was the GOP’s I-frame, but when I modify my commands as :

  ffmpeg -ss 526.623 -t 347 -i 'example.mp4' -c copy -avoid_negative_ts 1 -y res.mp4

  Output shows time=00:05:46.99 and actual video length is 00:05:52.13

  In the first case it added 5.13sec, in the second 5.14. Let’s take 5.14 for both cases that show that it has nothing to do with I-frame. There is no magic in this world (I guess). But what then ?

  UPD : It is GOP in the begging of the video. For this video it’s about 7 seconds.

• Android Java — Using and building FFMPEG library in Android Studio(Cmake)

  12 septembre 2017, par y3k00000

  As title, I’m trying to use the ffmpeg source code as library in Android Studio on Ubuntu Linux, but meeting some trouble in compilation stage. I think I must be missing some compile option but having no idea what I miss, can somebody lend a hand ?

  My codes & settings are below :

  A simple auto-generated .cpp

  #include 
  
  #include <string>
  
  #include "libavcodec/aacenc.h"
  
  
  
  extern "C"
  
  JNIEXPORT jstring JNICALL
  
  Java_y3k_testffmpegnative_MainActivity_stringFromJNI(
  
          JNIEnv *env,
  
          jobject /* this */) {
  
      std::string hello = "Hello from C++";
  
      return env->NewStringUTF(hello.c_str());
  
  }
  
  
  
  AACEncContext * aacEncContext; // Just trying by adding this.
  
  </string>

  I’ve tried these Gradle setting and it didn’t help :

  android {
  
      ....
  
      externalNativeBuild {
  
          cmake {
  
              arguments "-DANDROID_TOOLCHAIN=clang"
  
              cFlags "-std=c99"
  
              cppFlags "-frtti","-fexceptions"
  
          }
  
      }
  
  }
  
  ....

  CMakeLists.txt

  (Android Studio generated)
  
  ....
  
  include_directories( /home/y3k/ffmpeg )

  Error message while compiling :

  /home/y3k/ffmpeg/libavutil/float_dsp.h
  
  Error:(164, 50) error: expected ')'
  
  Information:(164, 30) to match this '('
  
  Error:(164, 50) error: expected ')'
  
  Information:(164, 30) note: to match this '('
  
  /home/y3k/ffmpeg/libavutil/fixed_dsp.h
  
  Error:(153, 44) error: expected ')'
  
  Information:(153, 30) to match this '('
  
  Error:(153, 44) error: expected ')'
  
  Information:(153, 30) note: to match this '('
  
  /home/y3k/ffmpeg/libavcodec/mpeg4audio.h
  
  Error:(44, 8) error: unknown type name 'av_export'
  
  Error:(44, 18) error: expected unqualified-id
  
  Error:(44, 8) error: unknown type name 'av_export'
  
  Error:(44, 18) error: expected unqualified-id
  
  /home/y3k/ffmpeg/libavcodec/aac.h
  
  Error:(294, 21) error: expected member name or ';' after declaration specifiers
  
  Error:(294, 21) error: expected member name or ';' after declaration specifiers

  FFMpeg config.h generated by this script :

  NDK=/home/y3k/Android/Sdk/ndk-bundle
  
  SYSROOT=$NDK/platforms/android-23/arch-arm/
  
  TOOLCHAIN=$NDK/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64
  
  function build_one
  
  {
  
  ./configure \
  
   --prefix=$PREFIX \
  
   --disable-shared \
  
   --enable-static \
  
   --disable-doc \
  
   --disable-ffmpeg \
  
   --disable-ffplay \
  
   --disable-ffprobe \
  
   --disable-ffserver \
  
   --disable-avdevice \
  
   --disable-doc \
  
   --disable-symver \
  
   --cross-prefix=$TOOLCHAIN/bin/arm-linux-androideabi- \
  
   --target-os=linux \
  
   --arch=arm \
  
   --enable-cross-compile \
  
   --sysroot=$SYSROOT \
  
   --extra-cflags="-Os -fpic $ADDI_CFLAGS" \
  
   --extra-ldflags="$ADDI_LDFLAGS" \
  
   $ADDITIONAL_CONFIGURE_FLAG
  
  make clean
  
  make
  
  make install
  
  }
  
  CPU=arm
  
  PREFIX=$(pwd)/android/$CPU
  
  ADDI_CFLAGS="-marm"
  
  build_one

  By tracing the errors I found these lines :

  in float_dsp.h, fixed_dsp.h :

  void (*butterflies_float)(float *av_restrict v1, float *av_restrict v2, int len);

  av_restrict defined in config.h

  #define av_restrict restrict

  in aac.h :

  ....
  
  struct AACContext {
  
      AVClass        *class;
  
  ....

  in mpeg4audio.h :

  extern av_export const int avpriv_mpeg4audio_sample_rates[16];

  So I’m guessing it’s because the compiler misrecognized the C code as C++, I tried adding these :

  arguments "-DANDROID_TOOLCHAIN=clang"
  
  cFlags "-std=c99"

  to my build.gradle but didn’t help. Having no idea where to move on. :(

  I’m using the latest stable version of Android Studio on Ubuntu desktop. Please don’t be hesitate to ask if any extra information is required.

  Also I’ve been tried edit my native-lib.cpp into .c (Surely with the code contents changed), but wasn’t working either.

  Appreciate for any help.