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• Grand Unified Theory of Compact Disc

  1er février 2013, par Multimedia Mike — General

  This is something I started writing about a decade ago (and I almost certainly have some of it wrong), back when compact discs still had a fair amount of relevance. Back around 2002, after a few years investigating multimedia technology, I took an interest in compact discs of all sorts. Even though there may seem to be a wide range of CD types, I generally found that they’re all fundamentally the same. I thought I would finally publishing something, incomplete though it may be.

  Physical Perspective
  There are a lot of ways to look at a compact disc. First, there’s the physical format, where a laser detects where pits/grooves have disturbed the smooth surface (a.k.a. lands). A lot of technical descriptions claim that these lands and pits on a CD correspond to ones and zeros. That’s not actually true, but you have to decide what level of abstraction you care about, and that abstraction is good enough if you only care about the discs from a software perspective.

  Grand Unified Theory (Software Perspective)
  Looking at a disc from a software perspective, I have generally found it useful to view a CD as a combination of a 2 main components :

  • table of contents (TOC)
  • a long string of sectors, each of which is 2352 bytes long

  I like to believe that’s pretty much all there is to it. All of the information on a CD is stored as a string of sectors that might be chopped up into a series of anywhere from 1-99 individual tracks. The exact sector locations where these individual tracks begin are defined in the TOC.

  Audio CDs (CD-DA / Red Book)
  The initial purpose for the compact disc was to store digital audio. The strange sector size of 2352 bytes is an artifact of this original charter. “CD quality audio”, as any multimedia nerd knows, is formally defined as stereo PCM samples that are each 16 bits wide and played at a frequency of 44100 Hz.
  

  (44100 audio frames / 1 second) * (2 samples / audio frame) * 
    (16 bits / 1 sample) * (1 byte / 8 bits) = 176,400 bytes / second
  (176,400 bytes / 1 second) / (2352 bytes / 1 sector) = 75
  

  75 is the number of sectors required to store a single second of CD-quality audio. A single sector stores 1/75th of a second, or a ‘frame’ of audio (though I think ‘frame’ gets tossed around at all levels when describing CD formats).

  The term “red book” is thrown around in relation to audio CDs. There is a series of rainbow books that define various optical disc standards and the red book describes audio CDs.

  Basic Data CD-ROMs (Mode 1 / Yellow Book)
  Somewhere along the line, someone decided that general digital information could be stored on these discs. Hence, the CD-ROM was born. The standard model above still applies– TOC and string of 2352-byte sectors. However, it’s generally only useful to have a single track on a CD-ROM. Thus, the TOC only lists a single track. That single track can easily span the entire disc (something that would be unusual for a typical audio CD).

  While the model is mostly the same, the most notable difference between and audio CD and a plain CD-ROM is that, while each sector is 2352 bytes long, only 2048 bytes are used to store actual data payload. The remaining bytes are used for synchronization and additional error detection/correction.

  At least, the foregoing is true for mode 1 / form 1 CD-ROMs (which are the most common). “Mode 1″ CD-ROMs are defined by a publication called the yellow book. There is also mode 1 / form 2. This forgoes the additional error detection and correction afforded by form 1 and dedicates 2336 of the 2352 sector bytes to the data payload.

  CD-ROM XA (Mode 2 / Green Book)
  From a software perspective, these are similar to mode 1 CD-ROMs. There are also 2 forms here. The first form gives a 2048-byte data payload while the second form yields a 2324-byte data payload.

  Video CD (VCD / White Book)
  These are CD-ROM XA discs that carry MPEG-1 video and audio data.

  Photo CD (Beige Book)
  This is something I have never personally dealt with. But it’s supposed to conform to the CD-ROM XA standard and probably fits into my model. It seems to date back to early in the CD-ROM era when CDs were particularly cost prohibitive.

  Multisession CDs (Blue Book)
  Okay, I admit that this confuses me a bit. Multisession discs allow a user to burn multiple sessions to a single recordable disc. I.e., burn a lump of data, then burn another lump at a later time, and the final result will look like all the lumps were recorded as the same big lump. I remember this being incredibly useful and cost effective back when recordable CDs cost around US$10 each (vs. being able to buy a spindle of 100 CD-Rs for US$10 or less now). Studying the cdrom.h file for the Linux OS, I found a system call named CDROMMULTISESSION that returns the sector address of the start of the last session. If I were to hypothesize about how to make this fit into my model, I might guess that the TOC has some hint that the disc was recorded in multisession (which needs to be decided up front) and the CDROMMULTISESSION call is made to find the last session. Or it could be that a disc read initialization operation always leads off with the CDROMMULTISESSION query in order to determine this.

  I suppose I could figure out how to create a multisession disc with modern software, or possibly dig up a multisession disc from 15+ years ago, and then figure out how it should be read.

  CD-i
  This type puzzles my as well. I do have some CD-i discs and I thought that I could read them just fine (the last time I looked, which was many years ago). But my research for this blog post has me thinking that I might not have been seeing the entire picture when I first studied my CD-i samples. I was able to see some of the data, but sources indicate that only proper CD-i hardware is able to see all of the data on the disc (apparently, the TOC doesn’t show all of the sectors on disc).

  Hybrid CDs (Data + Audio)
  At some point, it became a notable selling point for an audio CD to have a data track with bonus features. Even more common (particularly in the early era of CD-ROMs) were computer and console games that used the first track of a disc for all the game code and assets and the remaining tracks for beautifully rendered game audio that could also be enjoyed outside the game. Same model : TOC points to the various tracks and also makes notes about which ones are data and which are audio.

  There seems to be 2 distinct things described above. One type is the mixed mode CD which generally has the data in the first track and the audio in tracks 2..n. Then there is the enhanced CD, which apparently used multisession recording and put the data at the end. I think that the reasoning for this is that most audio CD player hardware would only read tracks from the first session and would have no way to see the data track. This was a positive thing. By contrast, when placing a mixed-mode CD into an audio player, the data track would be rendered as nonsense noise.

  Subchannels
  There’s at least one small detail that my model ignores : subchannels. CDs can encode bits of data in subchannels in sectors. This is used for things like CD-Text and CD-G. I may need to revisit this.

  In Summary
  There’s still a lot of ground to cover, like how those sectors might be formatted to show something useful (e.g., filesystems), and how the model applies to other types of optical discs. Sounds like something for another post.

• How can I crop a video on Android phone

  13 août 2014, par Dnaso

  I am currently making an application where I need to crop a video in a square. I already made my surface preview display a square with strategically placed overlays (making the surface iew a square distorts the video). After I save it to the path and before uploading to my server, is there a way I can crop the bounds (Like bitmap cropping) and then upload it to my server. I can use ffmpeg but that gets server intensive with a lot of users and is not a viable solution.

  Any guidance would be much appreciated.

• android ffmpeg bad video output

  20 août 2014, par Sujith Manjavana

  I’m following this tutorial to create my first ffmpeg app. I have successfully build the shared libs and compiled the project without any errors. But when i run the app on my nexus 5 the output is this

  Here is the native code

  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libswscale></libswscale>swscale.h>
  
  #include <libavutil></libavutil>pixfmt.h>
  
  
  
  #include 
  
  #include 
  
  
  
  #include 
  
  #include <android></android>native_window.h>
  
  #include <android></android>native_window_jni.h>
  
  
  
  #define LOG_TAG "android-ffmpeg-tutorial02"
  
  #define LOGI(...) __android_log_print(4, LOG_TAG, __VA_ARGS__);
  
  #define LOGE(...) __android_log_print(6, LOG_TAG, __VA_ARGS__);
  
  
  
  ANativeWindow*      window;
  
  char                *videoFileName;
  
  AVFormatContext     *formatCtx = NULL;
  
  int                 videoStream;
  
  AVCodecContext      *codecCtx = NULL;
  
  AVFrame             *decodedFrame = NULL;
  
  AVFrame             *frameRGBA = NULL;
  
  jobject             bitmap;
  
  void*               buffer;
  
  struct SwsContext   *sws_ctx = NULL;
  
  int                 width;
  
  int                 height;
  
  int                 stop;
  
  
  
  jint naInit(JNIEnv *pEnv, jobject pObj, jstring pFileName) {
  
      AVCodec         *pCodec = NULL;
  
      int             i;
  
      AVDictionary    *optionsDict = NULL;
  
  
  
      videoFileName = (char *)(*pEnv)->GetStringUTFChars(pEnv, pFileName, NULL);
  
      LOGI("video file name is %s", videoFileName);
  
      // Register all formats and codecs
  
      av_register_all();
  
      // Open video file
  
      if(avformat_open_input(&amp;formatCtx, videoFileName, NULL, NULL)!=0)
  
          return -1; // Couldn't open file
  
      // Retrieve stream information
  
      if(avformat_find_stream_info(formatCtx, NULL)&lt;0)
  
          return -1; // Couldn't find stream information
  
      // Dump information about file onto standard error
  
      av_dump_format(formatCtx, 0, videoFileName, 0);
  
      // Find the first video stream
  
      videoStream=-1;
  
      for(i=0; inb_streams; i++) {
  
          if(formatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO) {
  
              videoStream=i;
  
              break;
  
          }
  
      }
  
      if(videoStream==-1)
  
          return -1; // Didn't find a video stream
  
      // Get a pointer to the codec context for the video stream
  
      codecCtx=formatCtx->streams[videoStream]->codec;
  
      // Find the decoder for the video stream
  
      pCodec=avcodec_find_decoder(codecCtx->codec_id);
  
      if(pCodec==NULL) {
  
          fprintf(stderr, "Unsupported codec!\n");
  
          return -1; // Codec not found
  
      }
  
      // Open codec
  
      if(avcodec_open2(codecCtx, pCodec, &amp;optionsDict)&lt;0)
  
          return -1; // Could not open codec
  
      // Allocate video frame
  
      decodedFrame=avcodec_alloc_frame();
  
      // Allocate an AVFrame structure
  
      frameRGBA=avcodec_alloc_frame();
  
      if(frameRGBA==NULL)
  
          return -1;
  
      return 0;
  
  }
  
  
  
  jobject createBitmap(JNIEnv *pEnv, int pWidth, int pHeight) {
  
      int i;
  
      //get Bitmap class and createBitmap method ID
  
      jclass javaBitmapClass = (jclass)(*pEnv)->FindClass(pEnv, "android/graphics/Bitmap");
  
      jmethodID mid = (*pEnv)->GetStaticMethodID(pEnv, javaBitmapClass, "createBitmap", "(IILandroid/graphics/Bitmap$Config;)Landroid/graphics/Bitmap;");
  
      //create Bitmap.Config
  
      //reference: https://forums.oracle.com/thread/1548728
  
      const wchar_t* configName = L"ARGB_8888";
  
      int len = wcslen(configName);
  
      jstring jConfigName;
  
      if (sizeof(wchar_t) != sizeof(jchar)) {
  
          //wchar_t is defined as different length than jchar(2 bytes)
  
          jchar* str = (jchar*)malloc((len+1)*sizeof(jchar));
  
          for (i = 0; i &lt; len; ++i) {
  
              str[i] = (jchar)configName[i];
  
          }
  
          str[len] = 0;
  
          jConfigName = (*pEnv)->NewString(pEnv, (const jchar*)str, len);
  
      } else {
  
          //wchar_t is defined same length as jchar(2 bytes)
  
          jConfigName = (*pEnv)->NewString(pEnv, (const jchar*)configName, len);
  
      }
  
      jclass bitmapConfigClass = (*pEnv)->FindClass(pEnv, "android/graphics/Bitmap$Config");
  
      jobject javaBitmapConfig = (*pEnv)->CallStaticObjectMethod(pEnv, bitmapConfigClass,
  
              (*pEnv)->GetStaticMethodID(pEnv, bitmapConfigClass, "valueOf", "(Ljava/lang/String;)Landroid/graphics/Bitmap$Config;"), jConfigName);
  
      //create the bitmap
  
      return (*pEnv)->CallStaticObjectMethod(pEnv, javaBitmapClass, mid, pWidth, pHeight, javaBitmapConfig);
  
  }
  
  
  
  jintArray naGetVideoRes(JNIEnv *pEnv, jobject pObj) {
  
      jintArray lRes;
  
      if (NULL == codecCtx) {
  
          return NULL;
  
      }
  
      lRes = (*pEnv)->NewIntArray(pEnv, 2);
  
      if (lRes == NULL) {
  
          LOGI(1, "cannot allocate memory for video size");
  
          return NULL;
  
      }
  
      jint lVideoRes[2];
  
      lVideoRes[0] = codecCtx->width;
  
      lVideoRes[1] = codecCtx->height;
  
      (*pEnv)->SetIntArrayRegion(pEnv, lRes, 0, 2, lVideoRes);
  
      return lRes;
  
  }
  
  
  
  void naSetSurface(JNIEnv *pEnv, jobject pObj, jobject pSurface) {
  
      if (0 != pSurface) {
  
          // get the native window reference
  
          window = ANativeWindow_fromSurface(pEnv, pSurface);
  
          // set format and size of window buffer
  
          ANativeWindow_setBuffersGeometry(window, 0, 0, WINDOW_FORMAT_RGBA_8888);
  
      } else {
  
          // release the native window
  
          ANativeWindow_release(window);
  
      }
  
  }
  
  
  
  jint naSetup(JNIEnv *pEnv, jobject pObj, int pWidth, int pHeight) {
  
      width = pWidth;
  
      height = pHeight;
  
      //create a bitmap as the buffer for frameRGBA
  
      bitmap = createBitmap(pEnv, pWidth, pHeight);
  
      if (AndroidBitmap_lockPixels(pEnv, bitmap, &amp;buffer) &lt; 0)
  
          return -1;
  
      //get the scaling context
  
      sws_ctx = sws_getContext (
  
              codecCtx->width,
  
              codecCtx->height,
  
              codecCtx->pix_fmt,
  
              pWidth,
  
              pHeight,
  
              AV_PIX_FMT_RGBA,
  
              SWS_BILINEAR,
  
              NULL,
  
              NULL,
  
              NULL
  
      );
  
      // Assign appropriate parts of bitmap to image planes in pFrameRGBA
  
      // Note that pFrameRGBA is an AVFrame, but AVFrame is a superset
  
      // of AVPicture
  
      avpicture_fill((AVPicture *)frameRGBA, buffer, AV_PIX_FMT_RGBA,
  
              pWidth, pHeight);
  
      return 0;
  
  }
  
  
  
  void finish(JNIEnv *pEnv) {
  
      //unlock the bitmap
  
      AndroidBitmap_unlockPixels(pEnv, bitmap);
  
      av_free(buffer);
  
      // Free the RGB image
  
      av_free(frameRGBA);
  
      // Free the YUV frame
  
      av_free(decodedFrame);
  
      // Close the codec
  
      avcodec_close(codecCtx);
  
      // Close the video file
  
      avformat_close_input(&amp;formatCtx);
  
  }
  
  
  
  void decodeAndRender(JNIEnv *pEnv) {
  
      ANativeWindow_Buffer    windowBuffer;
  
      AVPacket                packet;
  
      int                     i=0;
  
      int                     frameFinished;
  
      int                     lineCnt;
  
      while(av_read_frame(formatCtx, &amp;packet)>=0 &amp;&amp; !stop) {
  
          // Is this a packet from the video stream?
  
          if(packet.stream_index==videoStream) {
  
              // Decode video frame
  
              avcodec_decode_video2(codecCtx, decodedFrame, &amp;frameFinished,
  
                 &amp;packet);
  
              // Did we get a video frame?
  
              if(frameFinished) {
  
                  // Convert the image from its native format to RGBA
  
                  sws_scale
  
                  (
  
                      sws_ctx,
  
                      (uint8_t const * const *)decodedFrame->data,
  
                      decodedFrame->linesize,
  
                      0,
  
                      codecCtx->height,
  
                      frameRGBA->data,
  
                      frameRGBA->linesize
  
                  );
  
                  // lock the window buffer
  
                  if (ANativeWindow_lock(window, &amp;windowBuffer, NULL) &lt; 0) {
  
                      LOGE("cannot lock window");
  
                  } else {
  
                      // draw the frame on buffer
  
                      LOGI("copy buffer %d:%d:%d", width, height, width*height*4);
  
                      LOGI("window buffer: %d:%d:%d", windowBuffer.width,
  
                              windowBuffer.height, windowBuffer.stride);
  
                      memcpy(windowBuffer.bits, buffer,  width * height * 4);
  
                      // unlock the window buffer and post it to display
  
                      ANativeWindow_unlockAndPost(window);
  
                      // count number of frames
  
                      ++i;
  
                  }
  
              }
  
          }
  
          // Free the packet that was allocated by av_read_frame
  
          av_free_packet(&amp;packet);
  
      }
  
      LOGI("total No. of frames decoded and rendered %d", i);
  
      finish(pEnv);
  
  }
  
  
  
  /**
  
   * start the video playback
  
   */
  
  void naPlay(JNIEnv *pEnv, jobject pObj) {
  
      //create a new thread for video decode and render
  
      pthread_t decodeThread;
  
      stop = 0;
  
      pthread_create(&amp;decodeThread, NULL, decodeAndRender, NULL);
  
  }
  
  
  
  /**
  
   * stop the video playback
  
   */
  
  void naStop(JNIEnv *pEnv, jobject pObj) {
  
      stop = 1;
  
  }
  
  
  
  jint JNI_OnLoad(JavaVM* pVm, void* reserved) {
  
      JNIEnv* env;
  
      if ((*pVm)->GetEnv(pVm, (void **)&amp;env, JNI_VERSION_1_6) != JNI_OK) {
  
           return -1;
  
      }
  
      JNINativeMethod nm[8];
  
      nm[0].name = "naInit";
  
      nm[0].signature = "(Ljava/lang/String;)I";
  
      nm[0].fnPtr = (void*)naInit;
  
  
  
      nm[1].name = "naSetSurface";
  
      nm[1].signature = "(Landroid/view/Surface;)V";
  
      nm[1].fnPtr = (void*)naSetSurface;
  
  
  
      nm[2].name = "naGetVideoRes";
  
      nm[2].signature = "()[I";
  
      nm[2].fnPtr = (void*)naGetVideoRes;
  
  
  
      nm[3].name = "naSetup";
  
      nm[3].signature = "(II)I";
  
      nm[3].fnPtr = (void*)naSetup;
  
  
  
      nm[4].name = "naPlay";
  
      nm[4].signature = "()V";
  
      nm[4].fnPtr = (void*)naPlay;
  
  
  
      nm[5].name = "naStop";
  
      nm[5].signature = "()V";
  
      nm[5].fnPtr = (void*)naStop;
  
  
  
      jclass cls = (*env)->FindClass(env, "roman10/tutorial/android_ffmpeg_tutorial02/MainActivity");
  
      //Register methods with env->RegisterNatives.
  
      (*env)->RegisterNatives(env, cls, nm, 6);
  
      return JNI_VERSION_1_6;
  
  }

  Here is the build.sh

  #!/bin/bash
  
  NDK=$HOME/Desktop/adt/android-ndk-r9
  
  SYSROOT=$NDK/platforms/android-9/arch-arm/
  
  TOOLCHAIN=$NDK/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64
  
  function build_one
  
  {
  
  ./configure \
  
      --prefix=$PREFIX \
  
      --enable-shared \
  
      --disable-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

  It works on the Galaxy tab2. what can i do to make it work on all devices ?? Please help me..