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• Manual encoding into MPEG-TS

  4 juillet 2014, par Lane

  SO...

  I am trying to take a H264 Annex B byte stream video and encode it into MPEG-TS in pure Java. My goals is to create a minimal MPEG-TS, Single Program, valid stream and to not include any timing information information (PCR, PTS, DTS).

  I am currently at the point where my generated file can be passed to ffmpeg (ffmpeg -i myVideo.ts) and ffmpeg reports...

  [NULL @ 0x7f8103022600] start time is not set in estimate_timings_from_pts
  
  
  
  Input #0, mpegts, from 'video.ts':
  
  Duration: N/A, bitrate: N/A
  
  Program 1 
  
    Stream #0:0[0x100]: Video: h264 (Main) ([27][0][0][0] / 0x001B), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc

  ...it seems like this warning for start time is not a big deal... and ffmpeg is unable to determine how long the video is. If I create another mpeg-ts file from my video file (ffmpeg -i myVideo.ts -vcodec copy validVideo.ts) and run ffmpeg -i validVideo.ts I get...

  Input #0, mpegts, from 'video2.ts':
  
  Duration: 00:00:11.61, start: 1.400000, bitrate: 3325 kb/s
  
  Program 1 
  
    Metadata:
  
      service_name    : Service01
  
      service_provider: FFmpeg
  
    Stream #0:0[0x100]: Video: h264 (Main) ([27][0][0][0] / 0x001B), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc

  ...so you can see the timing information and bitrate is there and so is the metadata.

  My H264 video is comprised of only I and P Frames (with the SPS and PPS preceding the I Frame of course) and the way that I am creating my MPEG-TS stream is...

  1. Write a single PAT at the beginning of the file
  2. Write a single PMT at the beginning of the file
  3. Create TS and PES packets from SPS, PPS and I Frame (AUD NALs too, if this is required ?)
  4. Create TS and PES packets from P Frame (again, AUD NALs too, if required)
  5. For the last payload of either an I Frame or P Frame, add filler bytes to an adaptation field to make sure it fits into a full TS packet
  6. Repeat 3-5 for the entire file

  ...my PAT looks like this...

  4740 0010 0000 b00d 0001 c100 0000 01f0
  
  002a b104 b2ff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff

  ...and my PMT looks like this...

  4750 0010
  
  0002 b012 0001 c100 00ff fff0 001b e100
  
  f000 c15b 41e0 ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff

  ...notice after the c100 00, the "ff ff", f0... says that we are not using a PCR... Also notice that I have updated my CRC to reflect this change to the PMT. My first I Frame packet looks like...

  4741 0010 0000 01e0
  
  0000 8000 0000 0000 0109 f000 0000 0127
  
  4d40 288d 8d60 2802 dd80 b501 0101 4000
  
  00fa 4000 3a98 3a18 00b7 2000 3380 2ef2
  
  e343 0016 e400 0670 05de 5c16 345d c000
  
  0000 0128 ee3c 8000 0000 0165 8880 0020
  
  0000 4fe5 63b5 4e90 b11c 9f8f f891 10f3
  
  13b1 666b 9fc6 03e9 e321 36bf 1788 347b
  
  eb23 fc89 5772 6e2e 1714 96df ed16 9b30
  
  252d ceb7 07e9 a0c7 c6e7 9515 be87 2df1
  
  81f3 b9d2 ba5f 243e 2d5c cba2 8ca5 b798
  
  6bec 8c43 0b5d bbda bc5b 6e7c e15c 84e8
  
  2f13 be84 

  ...you’ll notice after the 01e0 0000, 8000 00 is the PES header extension where I specify no PTS / DTS and the remaining length is zero. My first P Frame packet looks like...

  4741 001d
  
  0000 01e0 0000 8000 0000 0000 0109 f000
  
  0000 0141 9a00 0200 0593 ff45 a7ae 1acd
  
  f2d7 f9ec 557f cdb6 ba38 60d6 a626 5edb
  
  4bb9 9783 89e2 d7e1 102e 4625 2fbf ce16
  
  f952 d8c9 f027 e55a 6b2a 81c3 48d4 6a45
  
  050a f355 fbec db01 6562 6405 04aa e011
  
  50ec 0b45 45e5 0df7 2fed a3f8 ac13 2e69
  
  6739 6d81 f13d 2455 e6ca 1c6b dc96 65d5
  
  3bad f250 7dab 42e4 7ba9 f564 ee61 29fb
  
  1b2c 974c 6924 1a1f 99ef 063c b99a c507
  
  8c22 b0f8 b14c 3e4d 01d0 6120 4e19 8725
  
  2fda 6550 f907 3f87

  ...and whenever an I Frame or P Frame is ending, I have a TS packet with an adaptation field like...

  4701 003c b000 ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff ffff ffff
  
  ffff ffff ffff ffff ffff ffff

  ...where the first b0 bytes are the adaptation field stuffing bytes and the remaining ones are the final bytes of the I or P Frame. So as you can tell I can use ffmpeg and pass it my file to create a valid movie in any format. However, I need the file I create to be in the proper format and I cannot quite figure out what the last piece I am missing is. Any ideas ?

• Using libav to encode RGBA frames into MP4 but the output is a mess

  5 octobre 2019, par Cu2S

  I’m trying to decode a video into RGB frames, and then postprocess the frames, finally encode the frames into a video. But the output video is completely a mess :
  

  I wrote a minimal example to illustrate my idea. First, I read some information from some source video :

      AVFormatContext* inputFormatCtx = nullptr;
  
      int ret = avformat_open_input(&inputFormatCtx, inputParamsVideo, nullptr, nullptr);
  
      assert(ret >= 0);
  
      ret = avformat_find_stream_info(inputFormatCtx, NULL);
  
      av_dump_format(inputFormatCtx, 0, inputParamsVideo, 0);
  
  
  
      assert(ret >= 0);
  
      AVStream* inputVideoStream = nullptr;
  
      for (int i = 0; i < inputFormatCtx->nb_streams; i++)
  
      {
  
          const auto inputStream = inputFormatCtx->streams[i];
  
          if (inputStream->codec->codec_type == AVMEDIA_TYPE_VIDEO)
  
          {
  
              inputVideoStream = inputStream;
  
              break;
  
          }
  
      }
  
  
  
      assert(inputVideoStream != nullptr);
  
      AVCodecParameters* inputParams = inputVideoStream->codecpar;
  
      AVRational framerate = inputVideoStream->codec->framerate;
  
      auto gop_size = inputVideoStream->codec->gop_size;
  
      auto maxBFrames = inputVideoStream->codec->max_b_frames;

  Then I assign the information to the output stream :

  AVFormatContext *outputAVFormat = nullptr;
  
  avformat_alloc_output_context2(&outputAVFormat, nullptr, nullptr, kOutputPath);
  
  assert(outputAVFormat);
  
  AVCodec* codec = avcodec_find_encoder(outputAVFormat->oformat->video_codec);
  
  assert(codec);
  
  AVCodecContext* encodingCtx = avcodec_alloc_context3(codec);
  
  avcodec_parameters_to_context(encodingCtx, inputParams);
  
  encodingCtx->time_base = av_inv_q(framerate);
  
  encodingCtx->max_b_frames = maxBFrames;
  
  encodingCtx->gop_size = gop_size;
  
  
  
  
  
  if (outputAVFormat->oformat->flags & AVFMT_GLOBALHEADER)
  
      encodingCtx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
  
  AVStream* outStream = avformat_new_stream(outputAVFormat, nullptr);
  
  assert(outStream != nullptr);
  
  ret = avcodec_parameters_from_context(outStream->codecpar, encodingCtx);
  
  assert(ret >= 0);
  
  outStream->time_base = encodingCtx->time_base;

  Then I convert RGBA frames(which is read from files) into YUV420P via sws_scale, and encoding :

      ret = avcodec_open2(encodingCtx, codec, nullptr);
  
      assert(ret >= 0);
  
      av_dump_format(outputAVFormat, 0, kOutputPath, 1);
  
  
  
      ret = avio_open(&outputAVFormat->pb, kOutputPath, AVIO_FLAG_WRITE);
  
      assert(ret >= 0);
  
      ret = avformat_write_header(outputAVFormat, nullptr);
  
      assert(ret >= 0);
  
  
  
      AVFrame* frame = av_frame_alloc();
  
      frame->width = inputParams->width;
  
      frame->height = inputParams->height;
  
      frame->format = inputParams->format;
  
      frame->pts = 0;
  
      assert(ret >= 0);
  
  
  
      ret = av_frame_get_buffer(frame, 32);
  
      int frameCount = 0;
  
      assert(ret >= 0);
  
      ret = av_frame_make_writable(frame);
  
      assert(ret >= 0);
  
      SwsContext* swsContext = sws_getContext(inputParams->width, inputParams->height,
  
          AV_PIX_FMT_RGBA, frame->width,
  
          frame->height, static_cast<avpixelformat>(inputParams->format),
  
          SWS_BILINEAR, NULL, NULL, NULL);
  
  
  
  
  
      for (auto inputPicPath : std::filesystem::directory_iterator(kInputDir))
  
      {
  
          int width, height, comp;
  
          unsigned char* data = stbi_load(inputPicPath.path().string().c_str(), &amp;width, &amp;height, &amp;comp, 4);
  
          int srcStrides[1] = { 4 * width };
  
          int ret = sws_scale(swsContext, &amp;data, srcStrides, 0, height, frame->data,
  
              frame->linesize);
  
          assert(ret >= 0);
  
          frame->pts = frameCount;
  
          //frame->pict_type = AV_PICTURE_TYPE_I;
  
          frameCount += 1;
  
          encode(encodingCtx, frame, 0, outputAVFormat);
  
  
  
          stbi_image_free(data);
  
      }
  
  
  
      while (encode(encodingCtx, nullptr, 0, outputAVFormat))
  
      {
  
          ;
  
      }
  
  
  
      static bool encode(AVCodecContext* enc_ctx, AVFrame* frame, std::uint32_t streamIndex,
  
          AVFormatContext * formatCtx)
  
      {
  
          int ret;
  
          int got_output = 0;
  
          AVPacket packet = {};
  
          av_init_packet(&amp;packet);
  
          ret = avcodec_encode_video2(enc_ctx, &amp;packet, frame, &amp;got_output);
  
          assert(ret >= 0);
  
          if (got_output) {
  
              packet.stream_index = streamIndex;
  
              av_packet_rescale_ts(&amp;packet, enc_ctx->time_base, formatCtx->streams[streamIndex]->time_base);
  
              ret = av_interleaved_write_frame(formatCtx, &amp;packet);
  
              assert(ret >= 0);
  
              return true;
  
          }
  
          else {
  
              return false;
  
          }
  
      }
  
  </avpixelformat>

  Finally I cleaned up stuff :

      av_write_trailer(outputAVFormat);
  
      sws_freeContext(swsContext);
  
      avcodec_free_context(&encodingCtx);
  
      avio_closep(&outputAVFormat->pb);
  
      avformat_free_context(outputAVFormat);
  
      av_frame_free(&frame);

  I dumped my input format and my output format :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'H:\Me.MP4':
  
    Metadata:
  
      major_brand     : mp42
  
      minor_version   : 1
  
      compatible_brands: mp41mp42isom
  
      creation_time   : 2019-04-03T05:44:22.000000Z
  
    Duration: 00:00:06.90, start: 0.000000, bitrate: 1268 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 540x960, 1238 kb/s, 29.86 fps, 30 tbr, 600 tbn, 1200 tbc (default)
  
      Metadata:
  
        creation_time   : 2019-04-03T05:44:22.000000Z
  
        handler_name    : Core Media Video
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 8000 Hz, stereo, fltp, 24 kb/s (default)
  
      Metadata:
  
        creation_time   : 2019-04-03T05:44:22.000000Z
  
        handler_name    : Core Media Audio
  
  [libx264 @ 000002126F90C1C0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
  
  [libx264 @ 000002126F90C1C0] profile High, level 3.1, 4:2:0, 8-bit
  
  [libx264 @ 000002126F90C1C0] 264 - core 157 - H.264/MPEG-4 AVC codec - Copyleft 2003-2018 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=2 keyint=12 keyint_min=1 scenecut=40 intra_refresh=0 rc_lookahead=12 rc=abr mbtree=1 bitrate=1238 ratetol=1.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
  
  Output #0, mp4, to './output.mp4':
  
      Stream #0:0: Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 540x960, q=2-31, 1238 kb/s, 29.86 tbn

  Update :

  After I deleted

  encodingCtx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;

  the output video is right. Also, outputting avi works, too.

• Hacking the Popcorn Hour C-200

  3 mai 2010, par Mans — Hardware, MIPS

  Update : A new firmware version has been released since the publication of this article. I do not know if the procedure described below will work with the new version.

  The Popcorn Hour C-200 is a Linux-based media player with impressive specifications. At its heart is a Sigma Designs SMP8643 system on chip with a 667MHz MIPS 74Kf as main CPU, several co-processors, and 512MB of DRAM attached. Gigabit Ethernet, SATA, and USB provide connectivity with the world around it. With a modest $299 on the price tag, the temptation to repurpose the unit as a low-power server or cheap development board is hard to resist. This article shows how such a conversion can be achieved.
  

  Kernel

  The PCH runs a patched Linux 2.6.22.19 kernel. A source tarball is available from the manufacturer. This contains the sources with Sigma support patches, Con Kolivas’ patch set (scheduler tweaks), and assorted unrelated changes. Properly split patches are unfortunately not available. I have created a reduced patch against vanilla 2.6.22.19 with only Sigma-specific changes, available here.

  The installed kernel has a number of features disabled, notably PTY support and oprofile. We will use kexec to load a more friendly one.

  As might be expected, the PCH kernel does not have kexec support enabled. It does however, by virtue of using closed-source components, support module loading. This lets us turn kexec into a module and load it. A patch for this is available here. To build the module, apply the patch to the PCH sources and build using this configuration. This will produce two modules, kexec.ko and mips_kexec.ko. No other products of this build will be needed.

  The replacement kernel can be built from the PCH sources or, if one prefers, from vanilla 2.6.22.19 with the Sigma-only patch. For the latter case, this config provides a minimal starting point suitable for NFS-root.

  When configuring the kernel, make sure CONFIG_TANGOX_IGNORE_CMDLINE is enabled. Otherwise the command line will be overridden by a useless one stored in flash. A good command line can be set with CONFIG_CMDLINE (under “Kernel hacking” in menuconfig) or passed from kexec.

  Taking control

  In order to load our kexec module, we must first gain root privileges on the PCH, and here a few features of the system are working to our advantage :

  1. The PCH allows mounting any NFS export to access media files stored there.
  2. There is an HTTP server running. As root.
  3. This HTTP server can be readily instructed to fetch files from an NFS mount.
  4. Files with a name ending in .cgi are executed. As root.

  All we need do to profit from this is place the kexec modules, the kexec userspace tools, and a simple script on an NFS export. Once this is done, and the mount point configured on the PCH, a simple HTTP request will send the old kernel screaming to /dev/null, our shiny new kernel taking its place.

  The rootfs

  A kernel is mostly useless without a root filesystem containing tools and applications. A number of tools for cross-compiling a full system exist, each with its strengths and weaknesses. The only thing to look out for is the version of kernel headers used (usually a linux-headers package). As we will be running an old kernel, chances are the default version is too recent. Other than this, everything should be by the book.

  Assembling the parts

  Having gathered all the pieces, it is now time to assemble the hack. The following steps are suitable for an NFS-root system. Adaptation to a disk-based system is left as an exercise.

  1. Build a rootfs for MIPS 74Kf little endian. Make sure kernel headers used are no more recent than 2.6.22.x. Include a recent version of the kexec userspace tools.
  2. Fetch and unpack the PCH kernel sources.
  3. Apply the modular kexec patch.
  4. Using this config, build the modules and install them as usual to the rootfs. The version string must be 2.6.22.19-19-4.
  5. From either the same kernel sources or plain 2.6.22.19 with Sigma patches, build a vmlinux and (optionally) modules using this config. Modify the compiled-in command line to point to the correct rootfs. Set the version string to something other than in the previous step.
  6. Copy vmlinux to any directory in the rootfs.
  7. Copy kexec.sh and kexec.cgi to the same directory as vmlinux.
  8. Export the rootfs over NFS with full read/write permissions for the PCH.
  9. Power on the PCH, and update to latest firmware.
  10. Configure an NFS mount of the rootfs.
  11. Navigate to the rootfs in the PCH UI. A directory listing of bin, dev, etc. should be displayed.
  12. On the host system, run the kexec.sh script with the target hostname or IP address as argument.
  13. If all goes well, the new kernel will boot and mount the rootfs.

  Serial console

  A serial console is indispensable for solving boot problems. The PCH board has two UART connectors. We will use the one labeled UART0. The pinout is as follows (not standard PC pinout).

          +-----------+
         2| * * * * * |10
         1| * * * * * |9
          -----------+
            J7 UART0
      /---------------------/ board edge
  

  Pin	Function
  1	+5V
  5	Rx
  6	Tx
  10	GND

  The signals are 3.3V so a converter, e.g. MAX202, is required for connecting this to a PC serial port. The default port settings are 115200 bps 8n1.