Recherche avancée

Sur d’autres sites (5077)

• Fun With Tablets And Amazon’s App Store

  24 décembre 2011, par Multimedia Mike — General, amazon, android, app store, cyanogenmod, ios, smurfs, tablet

  I bought an Android tablet a few months ago. It is less expensive than the best tablets but no where near the bottom end of the market. I think it’s pretty good. However, one downside is that it’s not “certified” to use Google’s official marketplace. That would seem to be somewhat limiting, however…

  Enter Amazon’s Android App Store
  Amazon got into the business of selling Android Apps some time ago. I started experimenting with this on a Nexus One phone that Google gave me. When I installed the App Store on the Android tablet and logged in, I was pleasantly surprised to see all of my Amazon apps ready for downloading onto the tablet.

  So I have an App Store for use with this Android tablet.

  Anyway, the reason I bring this up is because I managed to screw up this tablet in an unusual and humorous manner. You might be wondering if an app downloaded from the Amazon App Store requires the App Store to be present in order to run. The answer is : Oh yeah ! It works like this :

  
  
  

  This means that if — perhaps out of curiosity, for example — you login to the Amazon App Store, download an app, install it, and then subsequently log out of the App Store or uninstall it altogether, the downloaded app will decline to run until you log back into the store.

  Here’s the thing– I wanted to provide a minimal level of security for my Android tablet. At the very least, I wished to lock the Amazon App Store itself since Amazon is famously (and, let’s face it, understandably) reluctant to deliberately add any friction to their shopping processes. I.e., without any external protection app, the App Store app would allow anyone to purchase any app using my tablet.

  So I purchased App Protector Pro from the Amazon App Store and it worked quite well. By default, it also password protects against modifying any system settings as well as installing new apps.

  So, here’s where I screwed up : App Protector Pro was doing its faithful duty and I uninstalled the Amazon App Store as an experiment. Suddenly, no apps obtained from the App Store would work unless I reinstalled the App Store. Okay, fair enough, except for one thing– App Protector Pro wouldn’t run without the App Store. Well, it did, it started to, tried to, but then exited. So I couldn’t re-install the App Store :

  
  
  Oops
  

  I eventually learned how to perform a factory reset of the unit which solved the problem. And, as indicated earlier, all of my apps were available for me to re-download.

  Modding, Cyanogen-style
  Open source aficionados will likely point out that there are alternate firmware options which allow me to take control of my Android tablet in a free and open manner. Among these options is CyanogenMod. After I got stuck in the situation described above, I thought I would have to resort to such an option.

  On the plus side, researching alternative firmware options is what taught me to boot the device into a recovery mode and ultimately restore to a factory default setting. But if you’ll allow me to indulge in a mini-rant regarding accessibility of open source software : I was more than a little frustrated in trying to understand what CyanogenMod could possibly offer me. Their homepage says it’s “an aftermarket firmware”. I’m not entirely sure what that means or how it can benefit me. Fortunately, they have a full feature list linked from the front page. They are, in order : Lockscreen gestures, phone goggles, OpenVPN, incognito mode, themes support, and DSP equalizer. I can’t say that any of those really add any value for me. I’d love to know if CyanogenMod supports Google Android Market and various other Google apps (such as maps and GMail). That’s a question that I can’t seem to find the answer to.

  The themes feature opens another old wound for me. Back around 1999 when I was first getting into Linux in a serious way, I remember that themes were a big theme at the Linux User Groups I would attend. I also remember lots are online articles at the time that emphasized how highly customizable the Linux desktop was in comparison to Windows 9x. I was bothered for 2 reasons : First, I thought there were more pressing problems that needed to be addressed in Linux ; and second, none of these customization options seemed particularly straightforward ; many apparently required hours of compiling and tinkering.

  Small digression. Anyway, back to CyanogenMod, I was glad to see that they prominently display a button in order to “View Video Tour”. Ah, internet video has us so spoiled these days. I was eager to see this aftermarket firmware in action to see what it could do for me. However, the link leads to… a forum post ? The thread seems to discuss how it would be a cool idea if the community could put together a video tour. At this point, the investigation just seems bizarre. It feels like a bunch of kids doing their best to do things the grown-up way.

  Okay, sorry, rant over. I try to stay positive these days. I’m sure the CyanogenMod folks are doing great, fun, and interesting work on their project. The problems they choose to solve might lack mainstream appeal, however.

  Free iPad
  Ultimately, I recently unloaded the little Android tablet because, well… when a free iPad comes your way, lower spec tablets feel a little silly to keep around. Yeah, it’s great to play around with. Though here’s one unsettling thing I noticed about Apple’s App Store. While browsing for worthwhile games to indulge in, I noticed that they had a section for “Top Grossing Games”. This was a separate list from the “Top Apps” charts. I found the list weird for 2 reasons : 1) Why do I care which games are raking in the most cash ? How does this communicate value to me, personally ? Seriously, why would I base a purchasing decision around which vendor has earned the most money ?

  Anyway, let’s move on to reason #2 this was scary : Most of the games in this list had a price of FREE. One of them was that Capcom Smurfs game that stirred up controversy some months ago because of kids making unsupervised in-app purchases of virtual smurfberries. I tend to think that a top-grossing, free to play game is probably one that heavily encourages in-app purchases. Strange how this emerging trend actually encourages me to seek out games from the “top paid” list vs. “top free”.

• FFMPEG : directly decode packets after encoding

  18 avril 2012, par user1282931

  using FFMPEG API, I try to encode a x264 video to a MP4 file with 0 frame latency and also, in realtime, show the currently encoded frame on screen (with encoding artifacts). The encoding to the file works, but so far I don't get the frames decoded right after writing them to the file. What I try is to feed the packetdata that is returned from avcodec_encode_video() right into avcodec_decode_video2() but the function returns -1 and the cmd output shows :

  [h264 @ 00000000025F0710] non-existing PPS 0 referenced
  
  [h264 @ 00000000025F0710] decode_slice_header error
  
  [h264 @ 00000000025F0710] no frame

  here is some code i use for encoding :

  AVPacket FFMpegEncoder2::write_video_frame(AVFrame* pic, int &numBytes)
  
  {
  
      int out_size, ret;
  
  
  
      AVPacket pkt;
  
  
  
  
  
      /* encode the image */
  
      out_size = avcodec_encode_video(m_cctx, m_outbuf,
  
                                          m_outbufSize, pic);
  
      /* If size is zero, it means the image was buffered. */
  
      assert(out_size>0) //0 frame delay
  
  
  
      av_init_packet(&pkt);
  
  
  
      if (m_cctx->coded_frame->pts != AV_NOPTS_VALUE)
  
            pkt.pts = av_rescale_q(m_cctx->coded_frame->pts,m_cctx->time_base, m_video_st->time_base);
  
      if (m_cctx->coded_frame->key_frame)
  
            pkt.flags |= AV_PKT_FLAG_KEY;
  
      pkt.stream_index = m_video_st->index;
  
      pkt.data         = m_outbuf;
  
      pkt.size         = out_size;
  
  
  
      /* Write the compressed frame to the media file. */
  
      ret = av_interleaved_write_frame(m_fctx, &pkt);
  
  
  
      if (ret != 0) {
  
          fprintf(stderr, "Error while writing video frame\n");
  
          exit(1);
  
      }
  
      numBytes = out_size;
  
      return pkt;
  
  }

  and then I take this returned packet and feed it into the decoder :

  const AVFrame* FFMpegDecoder2::decode(AVPacket* packet){
  
      AVPacket pkt;
  
      av_init_packet(&pkt);
  
      pkt.size = packet->size;
  
      pkt.data = packet->data;
  
  
  
      int len=0;
  
      int got_picture=0;
  
  
  
  
  
      while (pkt.size > 0) {
  
              len = avcodec_decode_video2(m_cctx, m_frame, &got_picture, &pkt);
  
              if (len < 0) {
  
                  fprintf(stderr, "Error while decoding frame %d\n", m_f);
  
                  exit(1);
  
              }
  
              if (got_picture) {
  
                  assert(pkt.size==len);
  
                  m_f++;
  
              }
  
              pkt.size -= len;
  
              pkt.data += len;
  
          }
  
      assert(got_picture);
  
      return m_frame;
  
  }

  but as stated, avcodec_decode_video2() returns -1

  what am I doing wrong ? Do i need to feed some headerdata into the decoder first somehow ?

  //edit :

  if i set

  m_formatCtx->oformat->flags &= ~AVFMT_GLOBALHEADER;
  
  m_codecctx->flags &= ~CODEC_FLAG_GLOBAL_HEADER;

  then i can decode the returned packet without error, but the written mp4 file will be black.

  //edit : this is how i setup the decoder :

  FFMpegDecoder2::FFMpegDecoder2(CodecID id)
  
      : m_codec(NULL)
  
      , m_cctx(NULL)
  
  {
  
  
  
  
  
      /* Initialize libavcodec, and register all codecs and formats. */
  
      avcodec_register_all();
  
  
  
      m_codec = avcodec_find_decoder(id);
  
      if (!m_codec) {
  
          fprintf(stderr, "codec not found\n");
  
          exit(1);
  
      }
  
  
  
      m_cctx = avcodec_alloc_context3(m_codec);
  
      m_cctx->codec = m_codec;
  
      m_cctx->pix_fmt = PIX_FMT_YUV420P;
  
  
  
      avcodec_open2(m_cctx, m_codec, NULL);
  
  
  
      //alloc frame
  
      m_frame = avcodec_alloc_frame();
  
  }

  this is what the memory window shows for the first packet (didn't copy all. the size of the first packet is 7859) :

  0x0000000002E66670  00 00 01 06 05 ff ff 55 dc 45 e9 bd e6 d9 48 b7 96 2c d8 20 d9 23 ee ef 78 32 36 34 20 2d 20 63 6f 72 65 20 31 32 30 20 72 32 31 34 36 20 62  .....ÿÿUÜEé.æÙH·–,Ø Ù#îïx264 - core 120 r2146 b
  
  0x0000000002E6669F  63 64 34 31 64 62 20 2d 20 48 2e 32 36 34 2f 4d 50 45 47 2d 34 20 41 56 43 20 63 6f 64 65 63 20 2d 20 43 6f 70 79 6c 65 66 74 20 32 30 30 33  cd41db - H.264/MPEG-4 AVC codec - Copyleft 2003
  
  0x0000000002E666CE  2d 32 30 31 31 20 2d 20 68 74 74 70 3a 2f 2f 77 77 77 2e 76 69 64 65 6f 6c 61 6e 2e 6f 72 67 2f 78 32 36 34 2e 68 74 6d 6c 20 2d 20 6f 70 74  -2011 - http://www.videolan.org/x264.html - opt
  
  0x0000000002E666FD  69 6f 6e 73 3a 20 63 61 62 61 63 3d 30 20 72 65 66 3d 33 20 64 65 62 6c 6f 63 6b 3d 31 3a 30 3a 30 20 61 6e 61 6c 79 73 65 3d 30 78 33 3a 30  ions: cabac=0 ref=3 deblock=1:0:0 analyse=0x3:0
  
  0x0000000002E6672C  78 31 31 33 20 6d 65 3d 68 65 78 20 73 75 62 6d 65 3d 34 20 70 73 79 3d 31 20 70 73 79 5f 72 64 3d 31 2e 30 30 3a 30 2e 30 30 20 6d 69 78 65  x113 me=hex subme=4 psy=1 psy_rd=1.00:0.00 mixe
  
  0x0000000002E6675B  64 5f 72 65 66 3d 31 20 6d 65 5f 72 61 6e 67 65 3d 31 36 20 63 68 72 6f 6d 61 5f 6d 65 3d 31 20 74 72 65 6c 6c 69 73 3d 30 20 38 78 38 64 63  d_ref=1 me_range=16 chroma_me=1 trellis=0 8x8dc
  
  0x0000000002E6678A  74 3d 31 20 63 71 6d 3d 30 20 64 65 61 64 7a 6f 6e 65 3d 32 31 2c 31 31 20 66 61 73 74 5f 70 73 6b 69 70 3d 31 20 63 68 72 6f 6d 61 5f 71 70  t=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp
  
  0x0000000002E667B9  5f 6f 66 66 73 65 74 3d 30 20 74 68 72 65 61 64 73 3d 31 20 73 6c 69 63 65 64 5f 74 68 72 65 61 64 73 3d 30 20 6e 72 3d 30 20 64 65 63 69 6d  _offset=0 threads=1 sliced_threads=0 nr=0 decim
  
  0x0000000002E667E8  61 74 65 3d 31 20 69 6e 74 65 72 6c 61 63 65 64 3d 30 20 62 6c 75 72 61 79 5f 63 6f 6d 70 61 74 3d 30 20 63 6f 6e 73 74 72 61 69 6e 65 64 5f  ate=1 interlaced=0 bluray_compat=0 constrained_
  
  0x0000000002E66817  69 6e 74 72 61 3d 30 20 62 66 72 61 6d 65 73 3d 30 20 77 65 69 67 68 74 70 3d 32 20 6b 65 79 69 6e 74 3d 32 35 20 6b 65 79 69 6e 74 5f 6d 69  intra=0 bframes=0 weightp=2 keyint=25 keyint_mi
  
  0x0000000002E66846  6e 3d 32 20 73 63 65 6e 65 63 75 74 3d 34 30 20 69 6e 74 72 61 5f 72 65 66 72 65 73 68 3d 30 20 72 63 3d 61 62 72 20 6d 62 74 72 65 65 3d 30  n=2 scenecut=40 intra_refresh=0 rc=abr mbtree=0
  
  0x0000000002E66875  20 62 69 74 72 61 74 65 3d 34 30 30 20 72 61 74 65 74 6f 6c 3d 31 2e 30 20 71 63 6f 6d 70 3d 30 2e 36 30 20 71 70 6d 69 6e 3d 30 20 71 70 6d   bitrate=400 ratetol=1.0 qcomp=0.60 qpmin=0 qpm
  
  0x0000000002E668A4  61 78 3d 36 39 20 71 70 73 74 65 70 3d 34 20 69 70 5f 72 61 74 69 6f 3d 31 2e 34 30 20 61 71 3d 31 3a 31 2e 30 30 00 80 00 00 00 01 65 88 84  ax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00.€....eˆ.
  
  0x0000000002E668D3  11 ef ff f8 22 0f 8a 00 02 09 7e 38 00 08 45 c7 00 01 1d c9 39 3d 87 ff e0 ac 13 03 6d 05 f1 00 10 00 10 12 88 04 00 04 02 60 70 4e 2d cc 38  .ïÿø".Š...~8..EÇ...É9=.ÿà¬..m.ñ.....ˆ....`pN-Ì8
  
  0x0000000002E66902  27 16 e6 07 21 1a e6 1c 84 6b 9f f0 f0 27 15 f2 7b 87 ff c1 58 2a 8a 00 04 b8 80 00 58 00 04 02 62 01 03 c1 c1 04 63 07 04 11 88 90 b1 89 0b  '.æ.!.æ..kŸðð'.ò{.ÿÁX*Š..¸€.X...b..ÁÁ.c...ˆ.±..
  
  0x0000000002E66931  1f 2c 11 02 b1 40 00 87 8f a4 f7 0f ff 82 b0 55 06 93 41 c4 10 51 00 00 40 14 00 04 00 a3 b7 35 b7 30 38 26 1e e6 1c 13 0f 73 f2 c1 10 2b 14  .,..±@...¤÷.ÿ.°U.“AÄ.Q..@....£·5·08&.æ...sòÁ.+.
  
  0x0000000002E66960  1f 1f 1c 32 7f 94 11 82 a1 40 01 f1 00 00 40 14 01 22 00 01 e0 1e 22 0a e3 83 1c 19 3d f8 7f e0 b0 16 03 01 22 0f 88 00 02 00 00 16 20 01 17  ...2.”..¡@.ñ..@.."..à.".ãƒ..=ø.à°...".ˆ..... ..
  
  0x0000000002E6698F  03 84 c2 5c 87 09 84 b9 06 4a e4 a4 ae 08 82 d8 e0 00 20 0f 1d 93 df c3 fe 0b 01 54 50 07 88 a8 80 00 64 09 88 58 88 58 83 84 1d 88 38 41 d8  ..Â\.....J䤮..Øà. ..“ßÃþ..TP.ˆ¨€.d.ˆXˆXƒ..ˆ8AØ
  
  0x0000000002E669BE  f2 c1 10 2b 14 00 08 f8 e0 00 62 38 64 ff 08 70 13 0a c1 d2 e9 b5 5d ba 10 80 09 a2 01 2e 07 04 c2 dc 87 04 c2 dc 81 c8 66 b9 0e 43 35 cb 0f  òÁ.+...øà.b8dÿ.p..ÁÒéµ]º.€.¢....ÂÜ..ÂÜ.Èf..C5Ë.
  
  0x0000000002E669ED  ff c1 10 27 2c 00 7e 8e 00 05 64 e4 f6 1f ff 82 28 a0 00 21 99 e3 80 00 99 ac 70 00 11 39 93 93 d8 7f fe 0a c1 40 34 9a 0b e3 40 00 84 40 01  ÿÁ.',.~Ž..däö.ÿ.( .!™ã€.™¬p..9““Ø.þ.Á@4š.ã@..@.
  
  0x0000000002E66A1C  00 01 02 88 fd cd 7d cc 0e 08 a4 dc c3 82 29 37 3f e0 88 14 8b f1 c3 1c 03 27 f0 c3 60 a0 50 62 86 da 36 1f 10 00 0a 80 00 80 14 40 00 20 00  ...ˆýÍ}Ì..¤ÜÃ.)7?àˆ..ñÃ..'ðÃ` Pb.Ú6....€.€.@. .

  and this is the encoders output (until after encoding frame 0) :

  [libx264 @ 00000000005ADAA0] using cpu capabilities: MMX2 SSE2Fast SSSE3 FastShu
  
  ffle SSE4.2
  
  [libx264 @ 00000000005ADAA0] profile High, level 3.0
  
  [libx264 @ 00000000005ADAA0] 264 - core 120 r2146 bcd41db - H.264/MPEG-4 AVC cod
  
  ec - Copyleft 2003-2011 - http://www.videolan.org/x264.html - options: cabac=0 r
  
  ef=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=4 psy=1 psy_rd=1.00:0.00 mixed
  
  _ref=1 me_range=16 chroma_me=1 trellis=0 8x8dct=1 cqm=0 deadzone=21,11 fast_pski
  
  p=1 chroma_qp_offset=0 threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 b
  
  luray_compat=0 constrained_intra=0 bframes=0 weightp=2 keyint=25 keyint_min=2 sc
  
  enecut=40 intra_refresh=0 rc=abr mbtree=0 bitrate=100 ratetol=1.0 qcomp=0.60 qpm
  
  in=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
  
  Output #0, mp4, to 'out2.mp4':
  
      Stream #0:0: Video: h264, yuv420p, 640x480, q=-1--1, 100 kb/s, 90k tbn, 25 t
  
  bc
  
  [mp4 @ 0000000000467570] Encoder did not produce proper pts, making some up.

• Improved thumbnail extraction from videos

  21 janvier 2014, par Tommy Ng

  I have been using FFmpeg to find the middle frame of a h264 video file, and extract the jpg thumbnail for use on a streaming portal. This is done automatically for each uploaded video.

  Sometimes the frame happens to be a black frame or just semantically bad i.e. a background or blurry shot which doesn't relate well to the video content.

  I wonder if I can use openCV or some other method/library to programmatically find better thumbnails through facial recognition or frame analysis.