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• Decoder return of av_find_best_stream vs. avcodec_find_decoder

  7 octobre 2016, par Jason C

  The docs for libav’s av_find_best_stream function (libav 11.7, Windows, i686, GPL) specify a parameter that can be used to receive a pointer to an appropriate AVCodec :

  decoder_ret - if non-NULL, returns the decoder for the selected stream

  There is also the avcodec_find_decoder function which can find an AVCodec given an ID.

  However, the official demuxing + decoding example uses av_find_best_stream to find a stream, but chooses to use avcodec_find_decoder to find the codec in lieu of av_find_best_stream’s codec return parameter :

  ret = av_find_best_stream(fmt_ctx, type, -1, -1, NULL, 0);
  
  ...
  
  stream_index = ret;
  
  st = fmt_ctx->streams[stream_index];
  
  ...
  
  /* find decoder for the stream */
  
  dec = avcodec_find_decoder(st->codecpar->codec_id);

  As opposed to something like :

  ret = av_find_best_stream(fmt_ctx, type, -1, -1, &dec, 0);

  My question is pretty straightforward : Is there a difference between using av_find_best_stream’s return parameter vs. using avcodec_find_decoder to find the AVCodec ?

  The reason I ask is because the example chose to use avcodec_find_decoder rather than the seemingly more convenient return parameter, and I can’t tell if the example did that for a specific reason or not. The documentation itself is a little spotty and disjoint, so it’s hard to tell if things like this are done for a specific important reason or not. I can’t tell if the example is implying that it "should" be done that way, or if the example author did it for some more arbitrary personal reason.

• texture rendering issue on iOS using OpenGL ES in Unity project

  28 mars 2016, par Time1ess

  I’m working on a project, part of it is to streaming video to my iPhone, currently I use my laptop to create the video stream to my iPhone with ffmpeg.The stream code in shell is below :

  ffmpeg \
  
      -f avfoundation -i "1" -s 1280*720 -r 29.97 \
  
      -c:v mpeg2video -q:v 20 -pix_fmt yuv420p -g 1 -threads 4\
  
      -f mpegts udp://192.168.1.102:6666

  with this, I successfully create my video stream.

  In Unity, I want to decode the video stream to create a texture. After I have gone through with some ffmpeg tutorial and Unity tutorial(Since I’m new to both of them), I followed tutorials and created my link library. Some of these codes are below(ask me if more is needed) :

  In my library :

  buffer alloc :

  uint8_t *buffer;
  
  int buffer_size;
  
  buffer_size = avpicture_get_size(AV_PIX_FMT_RGBA, VIEW_WIDTH, VIEW_HEIGHT);
  
  
  
  buffer = (uint8_t *) av_malloc(buffer_size*sizeof(uint8_t));
  
  
  
  avpicture_fill((AVPicture *) pFrameRGB, buffer, AV_PIX_FMT_RGBA,
  
                 VIEW_WIDTH, VIEW_HEIGHT);

  getContext :

      is->sws_ctx = sws_getContext
  
      (
  
       is->video_st->codec->width,
  
       is->video_st->codec->height,
  
       is->video_st->codec->pix_fmt,
  
       VIEW_WIDTH,
  
       VIEW_HEIGHT,
  
       AV_PIX_FMT_RGBA,
  
       SWS_BILINEAR,
  
       NULL,
  
       NULL,
  
       NULL
  
       );

  sws_scale :

  sws_scale(
  
            is->sws_ctx,
  
            (uint8_t const * const *)pFrame->data,
  
            pFrame->linesize,
  
            0,
  
            is->video_st->codec->height,
  
            pFrameRGB->data,
  
            pFrameRGB->linesize
  
            );

  texture render :

  static void UNITY_INTERFACE_API OnRenderEvent(int texID)
  
  {
  
      GLuint gltex = (GLuint)(size_t)(texID);
  
  
  
      glBindTexture(GL_TEXTURE_2D, gltex);
  
  
  
      glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, VIEW_WIDTH, VIEW_HEIGHT,
  
                      GL_RGBA, GL_UNSIGNED_BYTE, pFrameRGB->data[0]);
  
  
  
      glGetError();
  
      return;
  
  }
  
  
  
  extern "C" UnityRenderingEvent UNITY_INTERFACE_EXPORT UNITY_INTERFACE_API GetRenderEventFunc()
  
  {
  
      return OnRenderEvent;
  
  }

  In Unity :

  texture created :

      private Texture2D texture;
  
      private int texID;
  
      texture = new Texture2D (width, height, TextureFormat.RGBA32, false);
  
      texture.filterMode = FilterMode.Point;
  
      texture.Apply ();
  
      GetComponent<renderer> ().material.mainTexture = texture;
  
      texID = texture.GetNativeTexturePtr ().ToInt32();
  
  </renderer>

  update func :

      void Update ()
  
      {
  
          GL.IssuePluginEvent(GetRenderEventFunc(), texID);
  
      }

  Video stream info :

  Input #0, mpegts, from 'udp://0.0.0.0:6666':
  
    Duration: N/A, start: 2.534467, bitrate: N/A
  
    Program 1 
  
      Metadata:
  
        service_name    : Service01
  
        service_provider: FFmpeg
  
      Stream #0:0[0x100]: Video: mpeg2video (Main) ([2][0][0][0] / 0x0002), yuv420p(tv), 1280x720 [SAR 1:1 DAR 16:9], max. 104857 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc

  Leave other details, my library works fine on the Unity simulator, but when I compiled all my libraries for arm64 and used the xcode project that Unity created to build my app and ran it, I couldn’t get any texture rendered in my iPhone, I checkd my network and I’m sure that data had been sent to my iPhone and the Debug log showed me that frame has been successfully decoded also the OnRenderEvent func had been called.

  I’m confused and try to find answer on stackoverflow, maybe I’m a beginer cause I can’t find answers, so I ask you guys to help me plz.

  FYI :

  Unity 5.3.2f1 Personal

  Xcode 7.2.1

  iOS 9.2.1

  ffmpeg 3.0

• Android record screen and stream it

  15 novembre 2016, par Antonio C G

  I am working on a personal project in which I want to record the screen of my phone and stream it. It doesn’t have to record the whole, it can be just my app. I am trying to use ffmpeg, but I see that is not possible to read from /dev/graphics/fb0 as it requires root.

  I am trying to check what other options do I have. I know it must be possible, as there are other apps that do the same without the need of having a rooted device.

  I have just found this class https://developer.android.com/reference/android/media/projection/MediaProjection.html, that might be useful, but it is only available in API 21.

  Could you give me any tips of tools, or how could I achieve this ?

  Thanks.