Recherche avancée

Sur d’autres sites (4756)

• Dreamcast Serial Extractor

  31 décembre 2017, par Multimedia Mike — Sega Dreamcast

  It has not been a very productive year for blogging. But I started the year by describing an unfinished project that I developed for the Sega Dreamcast, so I may as well end the year the same way. The previous project was a media player. That initiative actually met with some amount of success and could have developed into something interesting if I had kept at it.

  By contrast, this post describes an effort that was ultimately a fool’s errand that I spent way too much time trying to make work.

  Problem Statement
  In my neverending quest to analyze the structure of video games while also hoarding a massive collection of them (though I’m proud to report that I did play at least a few of them this past year), I wanted to be able to extract the data from my many Dreamcast titles, both games and demo discs. I had a tool called the DC Coder’s Cable, a serial cable that enables communication between a Dreamcast and a PC. With the right software, you could dump an entire Dreamcast GD-ROM, which contained a gigabyte worth of sectors.

  Problem : The dumping software (named ‘dreamrip’ and written by noted game hacker BERO) operated in a very basic mode, methodically dumping sector after sector and sending it down the serial cable. This meant that it took about 28 hours to extract all the data on a single disc by running at the maximum speed of 115,200 bits/second, or about 11 kilobytes/second. I wanted to create a faster method.

  The Pitch
  I formed a mental model of dreamrip’s operation that looked like this :

  
  
  

  As an improvement, I envisioned this beautiful architecture :
  

  
  
  

  Architectural Assumptions
  My proposed architecture was predicated on the assumption that the disc reading and serial output functions were both I/O-bound operations and that the CPU would be idle much of the time. My big idea was to use that presumably idle CPU time to compress the sectors before sending them over the wire. As long as the CPU can compress the data faster than 11 kbytes/sec, it should be a win. In order to achieve this, I broke the main program into 3 threads :

  1. The first thread reads the sectors ; more specifically, it asks the drive firmware to please read the sectors and make the data available in system RAM
  2. The second thread waits for sector data to appear in memory and then compresses it
  3. The third thread takes the compressed data when it is ready and shuffles it out through the serial cable

  Simple and elegant, right ?

  For data track compression, I wanted to start with zlib in order to prove the architecture, but then also try bzip2 or lzma. As long as they could compress data faster than the serial port could write it, then it should be a win. For audio track compression, I wanted to use the Flake FLAC encoder. According to my notes, I did get both bzip2 compression and the Flake compressor working on the Dreamcast. I recall choosing Flake over the official FLAC encoder because it was much simpler and had fewer dependencies, always an important consideration for platforms such as this.

  Problems
  I worked for quite awhile on this project. I have a lot of notes recorded but a lot of the problems I had remain a bit vague in my memory. However, there was one problem I discovered that eventually sunk the entire initiative :

  The serial output operation is CPU-bound.

  My initial mental model was that the a buffer could be “handed off” to the serial subsystem and the CPU could go back to doing other work. Nope. Turns out that the CPU was participating at every step of the serial transfer.

  Further, I eventually dug into the serial driver code and learned that there was already some compression taking place via the miniLZO library.

  Lessons Learned

  • Recognize the assumptions that you’re making up front at the start of the project.
  • Prototype in order to ensure plausibility
  • Profile to make sure you’re optimizing the right thing (this is something I have learned again and again).

  Another interesting tidbit from my notes : it doesn’t matter how many sectors you read at a time, the overall speed is roughly the same. I endeavored to read 1000 2048-byte data sectors, 1 or 10 or 100 at a time, or all 1000 at once. My results :

  • 1 : 19442 ms
  • 10 : 19207 ms
  • 100 : 19194 ms
  • 1000 : 19320 ms

  No difference. That surprised me.

  Side Benefits
  At one point, I needed to understand how BERO’s dreamrip software was operating. I knew I used to have the source code but I could no longer find it. Instead, I decided to try to reverse engineer what I needed from the SH-4 binary image that I had. It wasn’t an ELF image ; rather, it was a raw binary meant to be loaded at a particular memory location which makes it extra challenging for ‘objdump’. This led to me asking my most viewed and upvoted question on Stack Overflow : “Disassembling A Flat Binary File Using objdump”. The next day, it also led me to post one of my most upvoted answers when I found the solution elsewhere.

  Strangely, I have since tried out the command line shown in my answer and have been unable to make it work. But people keep upvoting both the question and the answer.

  Eventually this all became moot when I discovered a misplaced copy of the source code on one of my computers.

  I strongly recall binging through the Alias TV show while I was slogging away on this project, so I guess that’s a positive association since I got so many fun screenshots out of it.

  The Final Resolution
  Strangely, I was still determined to make this project work even though the Dreamcast SD adapter arrived for me about halfway through the effort. Part of this was just stubbornness, but part of it was my assumptions about serial port speeds, in particular, my assumption that there was a certain speed-of-light type of limitation on serial port speeds so that the SD adapter, operating over the DC’s serial port, would not be appreciably faster than the serial cable.

  This turned out to be very incorrect. In fact, the SD adapter is capable of extracting an entire gigabyte disc image in 35-40 minutes. This is the method I have since been using to extract Dreamcast disc images.

  The post Dreamcast Serial Extractor first appeared on Breaking Eggs And Making Omelettes.

• ffmpeg drawtext RGB color codes

  19 janvier 2018, par Manish Jha

  I have an ffmpeg command which overlays an image and some text on a video where arguments are :

   -i "C:\exports\blue.mp4"
  
   -i "D:\Manish\Videos\logo.png" 
  
   -filter_complex 
  
   "[0:v]drawtext=fontfile='C\:\\Windows\\Fonts\\arial.ttf':
  
    text='falana dhimaka':
  
    fontcolor=AntiqueWhite:
  
    fontsize=20:x=1000:y=10[text]; 
  
    [text][1:v]overlay=140:5[filtered]" -map "[filtered]" -map 0:a? -codec:a copy 
  
    -preset ultrafast -ac 2 "C:\exports\blue_wm.mp4"

  This works well, but I want to be able to supply RGB Hex instead of AntiqueWhite. Any help is appreciated.

• How to set pts and dts of AVPacket from RTP timestamps while muxing VP8 RTP stream to webm using ffmpeg libavformat ?

  30 janvier 2018, par user2595786

  I am using ffmpeg libavformat library to write a video only webm file. I recieve VP8 encoded rtp stream on my server. I have successfully grouped the rtp byte stream (from rtp payload) into individual frames, and constructed a AVPacket. I am NOT re-encoding the payload to VP8 here as it is already vp8 encoded.

  I am writing the AVPacket to the file using av_write_interleaved() method. Though I am getting a webm file as output, it is not playing at all. When I checked for the info on the file using mkv tool’s ’mkvinfo’ command, I found the following info :

  + EBML head
  
  |+ EBML version: 1
  
  |+ EBML read version: 1
  
  |+ EBML maximum ID length: 4
  
  |+ EBML maximum size length: 8
  
  |+ Doc type: webm
  
  |+ Doc type version: 2
  
  |+ Doc type read version: 2
  
  + Segment, size 2142500
  
  |+ Seek head (subentries will be skipped)
  
  |+ EbmlVoid (size: 170)
  
  |+ Segment information
  
  | + Timestamp scale: 1000000
  
  | + Multiplexing application: Lavf58.0.100
  
  | + Writing application: Lavf58.0.100
  
  | + Duration: 78918744.480s (21921:52:24.480)
  
  |+ Segment tracks
  
  | + A track
  
  |  + Track number: 1 (track ID for mkvmerge & mkvextract: 0)
  
  |  + Track UID: 1
  
  |  + Lacing flag: 0
  
  |  + Name: Video Track
  
  |  + Language: eng
  
  |  + Codec ID: V_VP8
  
  |  + Track type: video
  
  |  + Default duration: 1.000ms (1000.000 frames/fields per second for a 
  
  video track)
  
  |  + Video track
  
  |   + Pixel width: 640
  
  |   + Pixel height: 480
  
  |+ Tags
  
  | + Tag
  
  |  + Targets
  
  |  + Simple
  
  |   + Name: ENCODER
  
  |   + String: Lavf58.0.100
  
  | + Tag
  
  |  + Targets
  
  |   + TrackUID: 1
  
  |  + Simple
  
  |   + Name: DURATION
  
  |   + String: 21921:52:24.4800000
  
  |+ Cluster

  As we can see, the duration of the stream is very disproportionately high. (My valid stream duration should be around 8-10 secs). And, the frame rate in the track info is also not what I am setting it to be. I am setting frame rate as 25 fps.

  I am applying av_scale_q(rtpTimeStamp, codec_timebase, stream_timebase) and setting the rescaled rtpTimeStamp as pts and dts values. My guess is my way of setting pts and dts is wrong. Please help me how to set pts and dts values on the AVPacket, so as get a working webm file with proper meta info on it.

  EDIT :

  The following is the code I call to init the library :

   #define STREAM_FRAME_RATE 25
  
   #define STREAM_PIX_FMT AV_PIX_FMT_YUV420P 
  
  
  
   typedef struct OutputStream {
  
     AVStream *st;
  
     AVCodecContext *enc;
  
     AVFrame *frame;
  
   } OutputStream;
  
  
  
  
  
   typedef struct WebMWriter {
  
        OutputStream *audioStream, *videoStream;
  
        AVFormatContext *ctx;
  
        AVOutputFormat *outfmt;
  
        AVCodec *audioCodec, *videoCodec;
  
   } WebMWriter;
  
  
  
   static OutputStream audioStream = { 0 }, videoStream = { 0 };
  
  
  
   WebMWriter *init(char *filename)
  
   {
  
      av_register_all();
  
  
  
      AVFormatContext *ctx = NULL;
  
      AVCodec *audioCodec = NULL, *videoCodec = NULL;
  
      const char *fmt_name = NULL;
  
      const char *file_name = filename;
  
  
  
      int alloc_status = avformat_alloc_output_context2(&ctx, NULL, fmt_name, file_name);
  
  
  
      if(!ctx)
  
              return NULL;
  
  
  
      AVOutputFormat *fmt = (*ctx).oformat;
  
  
  
      AVDictionary *video_opt = NULL;
  
      av_dict_set(&video_opt, "language", "eng", 0);
  
      av_dict_set(&video_opt, "title", "Video Track", 0);
  
  
  
      if(fmt->video_codec != AV_CODEC_ID_NONE)
  
      {
  
              addStream(&videoStream, ctx, &videoCodec, AV_CODEC_ID_VP8, video_opt);
  
      }
  
  
  
   if(videoStream.st)
  
              openVideo1(&videoStream, videoCodec, NULL);
  
  
  
      av_dump_format(ctx, 0, file_name, 1);
  
  
  
      int ret = -1;
  
      /* open the output file, if needed */
  
      if (!(fmt->flags & AVFMT_NOFILE)) {
  
              ret = avio_open(&ctx->pb, file_name, AVIO_FLAG_WRITE);
  
              if (ret < 0) {
  
                      printf("Could not open '%s': %s\n", file_name, av_err2str(ret));
  
                      return NULL;
  
              }
  
      }
  
  
  
      /* Write the stream header, if any. */
  
      AVDictionary *format_opt = NULL;
  
      ret = avformat_write_header(ctx, &format_opt);
  
      if (ret < 0) {
  
              fprintf(stderr, "Error occurred when opening output file: %s\n",
  
                              av_err2str(ret));
  
              return NULL;
  
      }
  
  
  
  
  
      WebMWriter *webmWriter = malloc(sizeof(struct WebMWriter));
  
      webmWriter->ctx = ctx;
  
      webmWriter->outfmt = fmt;
  
      webmWriter->audioStream = &audioStream;
  
      webmWriter->videoStream = &videoStream;
  
      webmWriter->videoCodec = videoCodec;
  
  
  
      return webmWriter;
  
   }

  The following is the openVideo() method :

   void openVideo1(OutputStream *out_st, AVCodec *codec, AVDictionary *opt_arg)
  
   {       
  
      AVCodecContext *codec_ctx = out_st->enc;
  
      int ret = -1;
  
      AVDictionary *opt = NULL;
  
      if(opt_arg != NULL)
  
      {       
  
              av_dict_copy(&opt, opt_arg, 0);
  
              ret = avcodec_open2(codec_ctx, codec, &opt);
  
      }
  
      else
  
      {       
  
              ret = avcodec_open2(codec_ctx, codec, NULL);
  
      }
  
  
  
      /* copy the stream parameters to the muxer */
  
      ret = avcodec_parameters_from_context(out_st->st->codecpar, codec_ctx);
  
      if (ret < 0) {
  
              printf("Could not copy the stream parameters\n");
  
              exit(1);
  
      }
  
  
  
   }

  The following is the addStream() method :

   void addStream(OutputStream *out_st, AVFormatContext *ctx, AVCodec **cdc, enum AVCodecID codecId, AVDictionary *opt_arg)
  
   {
  
  
  
      (*cdc) = avcodec_find_encoder(codecId);
  
      if(!(*cdc)) {
  
              exit(1);
  
      }
  
  
  
      /*as we are passing a NULL AVCodec cdc, So AVCodecContext codec_ctx will not be allocated, we have to do it explicitly */
  
      AVStream *st = avformat_new_stream(ctx, *cdc);
  
      if(!st) {
  
              exit(1);
  
      }
  
  
  
      out_st->st = st;
  
      st->id = ctx->nb_streams-1;
  
  
  
      AVDictionary *opt = NULL;
  
      av_dict_copy(&opt, opt_arg, 0);
  
      st->metadata = opt;
  
  
  
      AVCodecContext *codec_ctx = st->codec;
  
      if (!codec_ctx) {
  
              fprintf(stderr, "Could not alloc an encoding context\n");
  
              exit(1);
  
      }
  
      out_st->enc = codec_ctx;
  
  
  
      codec_ctx->strict_std_compliance = FF_COMPLIANCE_EXPERIMENTAL;
  
  
  
   switch ((*cdc)->type) {
  
              case AVMEDIA_TYPE_AUDIO:
  
                      codec_ctx->codec_id = codecId;
  
                      codec_ctx->sample_fmt  = AV_SAMPLE_FMT_FLTP;
  
                      codec_ctx->bit_rate    = 64000;
  
                      codec_ctx->sample_rate = 48000;
  
                      codec_ctx->channels    = 2;//1;
  
                      codec_ctx->channel_layout = AV_CH_LAYOUT_STEREO; 
  
                      codec_ctx->codec_type = AVMEDIA_TYPE_AUDIO;
  
                      codec_ctx->time_base = (AVRational){1,STREAM_FRAME_RATE};
  
  
  
  
  
                      break;
  
  
  
              case AVMEDIA_TYPE_VIDEO:
  
                      codec_ctx->codec_id = codecId;
  
                      codec_ctx->bit_rate = 90000;
  
                      codec_ctx->width    = 640;
  
                      codec_ctx->height   = 480;
  
  
  
  
  
                      codec_ctx->time_base = (AVRational){1,STREAM_FRAME_RATE};
  
                      codec_ctx->gop_size = 12;
  
                      codec_ctx->pix_fmt = STREAM_PIX_FMT;
  
                      codec_ctx->codec_type = AVMEDIA_TYPE_VIDEO;
  
  
  
                      break;
  
  
  
              default:
  
                      break;
  
      }
  
  
  
   /* Some formats want stream headers to be separate. */
  
      if (ctx->oformat->flags & AVFMT_GLOBALHEADER)
  
              codec_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
  
   }

  The following is the code I call to write a frame of data to the file :

   int writeVideoStream(AVFormatContext *ctx, AVStream *st, uint8_t *data, int size, long frameTimeStamp, int isKeyFrame, AVCodecContext *codec_ctx)
  
   {       
  
      AVRational rat = st->time_base;
  
      AVPacket pkt = {0};
  
      av_init_packet(&pkt);
  
  
  
      void *opaque = NULL;
  
      int flags = AV_BUFFER_FLAG_READONLY;
  
      AVBufferRef *bufferRef = av_buffer_create(data, size, NULL, opaque, flags);
  
  
  
      pkt.buf = bufferRef;
  
      pkt.data = data;
  
      pkt.size = size;  
  
      pkt.stream_index  = st->index;
  
  
  
      pkt.pts = pkt.dts = frameTimeStamp;
  
      pkt.pts = av_rescale_q(pkt.pts, codec_ctx->time_base, st->time_base);
  
      pkt.dts = av_rescale_q(pkt.dts, codec_ctx->time_base, st->time_base);
  
  
  
  
  
      if(isKeyFrame == 1)
  
              pkt.flags |= AV_PKT_FLAG_KEY;
  
  
  
      int ret = av_interleaved_write_frame(ctx, &pkt);
  
      return ret;
  
   }

  NOTE :
  Here ’frameTimeStamp’ is the rtp timeStamp on the rtp packet of that frame.

  EDIT 2.0 :

  My updated addStream() method with codecpars changes :

   void addStream(OutputStream *out_st, AVFormatContext *ctx, AVCodec **cdc, enum AVCodecID codecId, AVDictionary *opt_arg)
  
   {
  
  
  
      (*cdc) = avcodec_find_encoder(codecId);
  
      if(!(*cdc)) {
  
              printf("@@@@@ couldnt find codec \n");
  
              exit(1);
  
      }
  
  
  
      AVStream *st = avformat_new_stream(ctx, *cdc);
  
      if(!st) {
  
              printf("@@@@@ couldnt init stream\n");
  
              exit(1);
  
      }
  
  
  
      out_st->st = st;
  
      st->id = ctx->nb_streams-1;
  
      AVCodecParameters *codecpars = st->codecpar;
  
      codecpars->codec_id = codecId;
  
      codecpars->codec_type = (*cdc)->type;
  
  
  
      AVDictionary *opt = NULL;
  
      av_dict_copy(&opt, opt_arg, 0);
  
      st->metadata = opt;
  
      //av_dict_free(&opt);
  
  
  
      AVCodecContext *codec_ctx = st->codec;
  
      if (!codec_ctx) {
  
              fprintf(stderr, "Could not alloc an encoding context\n");
  
              exit(1);
  
      }
  
      out_st->enc = codec_ctx;
  
  
  
      //since opus is experimental codec
  
      //codec_ctx->strict_std_compliance = FF_COMPLIANCE_EXPERIMENTAL;
  
  
  
   switch ((*cdc)->type) {
  
              case AVMEDIA_TYPE_AUDIO:
  
                      codec_ctx->codec_id = codecId;
  
                      codec_ctx->sample_fmt  = AV_SAMPLE_FMT_FLTP;//AV_SAMPLE_FMT_U8 or AV_SAMPLE_FMT_S16;
  
                      codec_ctx->bit_rate    = 64000;
  
                      codec_ctx->sample_rate = 48000;
  
                      codec_ctx->channels    = 2;//1;
  
                      codec_ctx->channel_layout = AV_CH_LAYOUT_STEREO; //AV_CH_LAYOUT_MONO;
  
                      codec_ctx->codec_type = AVMEDIA_TYPE_AUDIO;
  
                      codec_ctx->time_base = (AVRational){1,STREAM_FRAME_RATE};
  
  
  
                      codecpars->format = codec_ctx->sample_fmt;
  
                      codecpars->channels = codec_ctx->channels;
  
                      codecpars->sample_rate = codec_ctx->sample_rate;
  
  
  
                      break;
  
  
  
              case AVMEDIA_TYPE_VIDEO:
  
                      codec_ctx->codec_id = codecId;
  
                      codec_ctx->bit_rate = 90000;
  
                      codec_ctx->width    = 640;
  
                      codec_ctx->height   = 480;
  
  
  
                      codec_ctx->time_base = (AVRational){1,STREAM_FRAME_RATE};
  
                      codec_ctx->gop_size = 12;
  
                      codec_ctx->pix_fmt = STREAM_PIX_FMT;
  
                      //codec_ctx->max_b_frames = 1;
  
                      codec_ctx->codec_type = AVMEDIA_TYPE_VIDEO;
  
                      codec_ctx->framerate = av_inv_q(codec_ctx->time_base);
  
                      st->avg_frame_rate = codec_ctx->framerate;//(AVRational){25000, 1000};
  
  
  
                      codecpars->format = codec_ctx->pix_fmt;
  
                      codecpars->width = codec_ctx->width;
  
                      codecpars->height = codec_ctx->height;
  
                      codecpars->sample_aspect_ratio = (AVRational){codec_ctx->width, codec_ctx->height};
  
  
  
                      break;
  
  
  
              default:
  
                      break;
  
      }      
  
      codecpars->bit_rate = codec_ctx->bit_rate;
  
  
  
      int ret = avcodec_parameters_to_context(codec_ctx, codecpars);
  
      if (ret < 0) {
  
              printf("Could not copy the stream parameters\n");
  
              exit(1);
  
      }
  
  
  
      /* Some formats want stream headers to be separate. */
  
      if (ctx->oformat->flags & AVFMT_GLOBALHEADER)
  
              codec_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
  
   }