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• Dreamcast Finds

  15 avril 2022, par Multimedia Mike — Sega Dreamcast

  Pursuant to my recent post about finally understanding how Sega Dreamcast GD-ROM rips are structured, I was able to prepare the contents of various demo discs in a manner that makes exploration easy via the Internet Archive. This is due to the way that IA makes it easy to browse archives such as ZIP or ISO files (anything that 7zip knows how to unpack), and also presents the audio tracks for native playback directly through the web browser.

  These are some of the interesting things I have found while perusing the various Dreamcast sampler discs.

  Multimedia Formats
  First and foremost : Multimedia-wise, SFD and ADX files abound on all the discs. SFD files are Sofdec, a middleware format used for a lot of FMV on Dreamcast games. These were little more than MPEG video files with a non-MPEG (ADPCM instead) audio codec. VLC will usually play the video portions of these files but has trouble detecting the audio. It’s not for lack of audio codec support because it can play the ADX files just fine.
  

  It should be noted that Dreamcast Magazine Disc 11 has an actual .mpg file (as opposed to a .sfd file) that has proper MPEG audio instead instead of ADX ADPCM.

  The only other multimedia format I know of that was used in any Dreamcast games was 4XM, used on Alone In The Dark : The New Nightmare. I wrote a simple C tool a long time to recover these files from a disc image I extracted myself. Rather than interpreting the ISO-9660 filesystem, the tool just crawled through the binary blob searching for ‘4XMV’ file signatures and using length data within the files for extraction.

  Also, there are plentiful PVR files (in reference to the PowerVR2 GPU hardware that the DC uses) which ‘file’ dutifully identifies as “Sega PVR image”. There are probably tools to view them. It doesn’t appear to be a complicated format.

  Scripting
  I was fascinated to see Lua files on at least one of the discs. It turns out that MDK 2 leverages the language, as several other games do. But it was still interesting to see the .lua files show up in the Dreamcast version as well.

  That Windows CE Logo
  Every Sega Dreamcast is famously emblazoned with a logo mentioning Microsoft Windows CE :

  
  
  

  It has confused many folks. It also confused me until this exploratory exercise. Many would wonder if the Dreamcast booted up into some Windows CE OS environment that then ran the game, but that certainly wasn’t it. Indeed, Dreamcast was one of the last consoles that really didn’t have any kind of hypervisor operating system managing everything.

  I found a file called rt2dc.exe on one sampler disc. At first, I suspected that this was a development utility for Windows to convert some “RT” graphical format into a format more suitable for the Dreamcast. Then, ‘file’ told me that it was actually a Windows EXE but compiled for the Hitachi SH-4 CPU (the brain inside the DC). Does the conversion utility run on the Dreamcast itself ? Then I analyzed the strings inside the binary and saw references to train stations. That’s when it started to click for me that this was the binary executable for the demo version of Railroad Tycoon 2 : Gold Edition, hence “rt2dc.exe”. Still, this provides some insight about whether Dreamcast “runs” Windows. This binary was built against a series of Windows CE libraries. The symbols also imply DirectX compatibility.

  Here is a page with more info about the WinCE/DirectX variant for the Sega Dreamcast. It seems that this was useful for closing the gap between PC and DC ports of games (i.e., being able to re-use more code between the 2 platforms). I guess this was part of what made Dreamcast a dry run for the DirectXbox (later Xbox).

  Here is a list of all the Dreamcast games that are known to use Windows CE.

  Suddenly, I am curious if tools such as IDA Pro or Ghidra can possibly open up Windows CE binaries that contain SH-4 code. Not that I’m particularly interested in reverse engineering any algorithms locked up in Dreamcast land.

  Tomb Raider Easter Egg
  The volume 6 sampler disc has a demo of Tomb Raider : The Last Revelation. While inspecting the strings, I found an Easter egg. I was far from the first person to discover it, though, as seen on this The Cutting Room Floor wiki page (look under “Developer Message”). It looks like I am the first person to notice it on the Dreamcast version. It shows up at offset 0xE3978 in the Dreamcast (demo version) binary, if anyone with permissions wants to update the page.

  Web Browser
  Then there’s the Web Browser for Sega Dreamcast. It seemed to be included on a lot of these sampler discs. But only mentioning the web browser undersells it– the thing also bundled an email client and an IRC client. It’s important to remember that the Dreamcast also had a keyboard peripheral.

  I need to check the timeline for when the web browser first became available vs. when the MIL-CD hack became known. My thinking is that there is no way that the web browser program didn’t have some security issues– buffer overflows and the like. It seems like this would have been a good method of breaking the security of the system.

  Ironically, I suddenly can think of a reason why one might want to use advanced reverse engineering tools on Dreamcast binaries, something I struggled with just a few paragraphs ago.

  Odds ‘n Ends
  It’s always fun to find plain text files among video game assets and speculating on the precise meaning… while also marveling how long people have been struggling to correctly spell “length”.

  Internationalization via plain text files.

  Another game (Slave Zero) saw fit to zip its assets. Maybe this was to save space in order to fit everything on the magazine sampler disc. Quizzically, this didn’t really save an appreciable amount of space.

  Finally, all the discs have an audio track 2 that advises that the disc must be played in a Dreamcast console. Not unusual. However, volume 4 also has a Japanese lady saying the same thing on track 4. This is odd because track 4 is one of the GD area audio tracks and is not accessible with normal CD hardware. Further, she identifies the disc as a “Windows CE disc”.

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

• Test if YouTube stream key is still active

  17 avril 2022, par codingmaster398

  I'm making a service to stream to YouTube, simply put.

  


  If the live stream ends or the stream key is no longer being used, we need to know. So far, it plays a short 3 second clip every once in a while, and if FFMpeg stops before it streams, we assume that the stream key is invalid. However, once we start a stream with the correct stream key, then end it and reset the stream key in another stream, the stream key still is being picked up as active.

  


  Is there any API to see if the stream key is still being used ?

  


• Assertion desc failed at src/libswscale/swscale_internal.h:764

  18 avril 2022, par harsh bhatnagar

  I am trying to implement the ffmpeg code written in C++ language .

  


  Tutorial link : https://www.youtube.com/watch?v=W6Yx3injNZs

  


  Github Reference : https://github.com/bartjoyce/video-app/tree/master/src

  


  When pass the filename or Rtsp Link in the avformat_open_input funcion. It shows the strange bug not able understand the issue in the C++ code or camera setting issue .

  


  // av_err2str returns a temporary array. This doesn't work in gcc.
// This function can be used as a replacement for av_err2str.
#include "video_reader.hpp"
static const char* av_make_error(int errnum) {
    static char str[AV_ERROR_MAX_STRING_SIZE];
    memset(str, 0, sizeof(str));
    return av_make_error_string(str, AV_ERROR_MAX_STRING_SIZE, errnum);
}

static AVPixelFormat correct_for_deprecated_pixel_format(AVPixelFormat pix_fmt) {
    // Fix swscaler deprecated pixel format warning
    // (YUVJ has been deprecated, change pixel format to regular YUV)
    switch (pix_fmt) {
        case AV_PIX_FMT_YUVJ420P: return AV_PIX_FMT_YUV420P;
        case AV_PIX_FMT_YUVJ422P: return AV_PIX_FMT_YUV422P;
        case AV_PIX_FMT_YUVJ444P: return AV_PIX_FMT_YUV444P;
        case AV_PIX_FMT_YUVJ440P: return AV_PIX_FMT_YUV440P;
        default:                  return pix_fmt;
    }
}

bool video_reader_open(VideoReaderState* state, const char* filename) {

    // Unpack members of state
    auto& width = state->width;
    auto& height = state->height;
    auto& time_base = state->time_base;
    auto& av_format_ctx = state->av_format_ctx;
    auto& av_codec_ctx = state->av_codec_ctx;
    auto& video_stream_index = state->video_stream_index;
    auto& av_frame = state->av_frame;
    auto& av_packet = state->av_packet;

    // Open the file using libavformat
    av_format_ctx = avformat_alloc_context();
    if (!av_format_ctx) {
        printf("Couldn't created AVFormatContext\n");
        return false;
    }

    if (avformat_open_input(&av_format_ctx, filename, NULL, NULL) != 0) {
        printf("Couldn't open video file\n");
        return false;
    }

    // Find the first valid video stream inside the file
    video_stream_index = -1;
    AVCodecParameters* av_codec_params;
    AVCodec* av_codec;
    for (int i = 0; i < av_format_ctx->nb_streams; ++i) {
        av_codec_params = av_format_ctx->streams[i]->codecpar;
        av_codec = avcodec_find_decoder(av_codec_params->codec_id);
        if (!av_codec) {
            continue;
        }
        if (av_codec_params->codec_type == AVMEDIA_TYPE_VIDEO) {
            video_stream_index = i;
            width = av_codec_params->width;
            height = av_codec_params->height;
            time_base = av_format_ctx->streams[i]->time_base;
            break;
        }
    }
    if (video_stream_index == -1) {
        printf("Couldn't find valid video stream inside file\n");
        return false;
    }

    // Set up a codec context for the decoder
    av_codec_ctx = avcodec_alloc_context3(av_codec);
    if (!av_codec_ctx) {
        printf("Couldn't create AVCodecContext\n");
        return false;
    }
    if (avcodec_parameters_to_context(av_codec_ctx, av_codec_params) < 0) {
        printf("Couldn't initialize AVCodecContext\n");
        return false;
    }
    if (avcodec_open2(av_codec_ctx, av_codec, NULL) < 0) {
        printf("Couldn't open codec\n");
        return false;
    }

    av_frame = av_frame_alloc();
    if (!av_frame) {
        printf("Couldn't allocate AVFrame\n");
        return false;
    }
    av_packet = av_packet_alloc();
    if (!av_packet) {
        printf("Couldn't allocate AVPacket\n");
        return false;
    }

    return true;
}

bool video_reader_read_frame(VideoReaderState* state, uint8_t* frame_buffer, int64_t* pts) {

    // Unpack members of state
    auto& width = state->width;
    auto& height = state->height;
    auto& av_format_ctx = state->av_format_ctx;
    auto& av_codec_ctx = state->av_codec_ctx;
    auto& video_stream_index = state->video_stream_index;
    auto& av_frame = state->av_frame;
    auto& av_packet = state->av_packet;
    auto& sws_scaler_ctx = state->sws_scaler_ctx;

    // Decode one frame
    int response;
    while (av_read_frame(av_format_ctx, av_packet) >= 0) {
        if (av_packet->stream_index != video_stream_index) {
            av_packet_unref(av_packet);
            continue;
        }

        response = avcodec_send_packet(av_codec_ctx, av_packet);
        if (response < 0) {
            printf("Failed to decode packet: %s\n", av_make_error(response));
            return false;
        }

        response = avcodec_receive_frame(av_codec_ctx, av_frame);
        if (response == AVERROR(EAGAIN) || response == AVERROR_EOF) {
            av_packet_unref(av_packet);
            continue;
        } else if (response < 0) {
            printf("Failed to decode packet: %s\n", av_make_error(response));
            return false;
        }

        av_packet_unref(av_packet);
        break;
    }

    *pts = av_frame->pts;
    
    // Set up sws scaler
    if (!sws_scaler_ctx) {
        auto source_pix_fmt = correct_for_deprecated_pixel_format(av_codec_ctx->pix_fmt);
        sws_scaler_ctx = sws_getContext(width, height, source_pix_fmt,
                                        width, height, AV_PIX_FMT_RGB0,
                                        SWS_BILINEAR, NULL, NULL, NULL);
    }
    if (!sws_scaler_ctx) {
        printf("Couldn't initialize sw scaler\n");
        return false;
    }

    uint8_t* dest[4] = { frame_buffer, NULL, NULL, NULL };
    int dest_linesize[4] = { width * 4, 0, 0, 0 };
    sws_scale(sws_scaler_ctx, av_frame->data, av_frame->linesize, 0, av_frame->height, dest, dest_linesize);

    return true;
}

bool video_reader_seek_frame(VideoReaderState* state, int64_t ts) {
    
    // Unpack members of state
    auto& av_format_ctx = state->av_format_ctx;
    auto& av_codec_ctx = state->av_codec_ctx;
    auto& video_stream_index = state->video_stream_index;
    auto& av_packet = state->av_packet;
    auto& av_frame = state->av_frame;
    
    av_seek_frame(av_format_ctx, video_stream_index, ts, AVSEEK_FLAG_BACKWARD);

    // av_seek_frame takes effect after one frame, so I'm decoding one here
    // so that the next call to video_reader_read_frame() will give the correct
    // frame
    int response;
    while (av_read_frame(av_format_ctx, av_packet) >= 0) {
        if (av_packet->stream_index != video_stream_index) {
            av_packet_unref(av_packet);
            continue;
        }

        response = avcodec_send_packet(av_codec_ctx, av_packet);
        if (response < 0) {
            printf("Failed to decode packet: %s\n", av_make_error(response));
            return false;
        }

        response = avcodec_receive_frame(av_codec_ctx, av_frame);
        if (response == AVERROR(EAGAIN) || response == AVERROR_EOF) {
            av_packet_unref(av_packet);
            continue;
        } else if (response < 0) {
            printf("Failed to decode packet: %s\n", av_make_error(response));
            return false;
        }

        av_packet_unref(av_packet);
        break;
    }

    return true;
}

void video_reader_close(VideoReaderState* state) {
    sws_freeContext(state->sws_scaler_ctx);
    avformat_close_input(&state->av_format_ctx);
    avformat_free_context(state->av_format_ctx);
    av_frame_free(&state->av_frame);
    av_packet_free(&state->av_packet);
    avcodec_free_context(&state->av_codec_ctx);
}


  


  Bug :

  


  [rtsp @ 0x55def0b00ac0] getaddrinfo(): Name or service not known
[rtsp @ 0x55def0b00ac0] max delay reached. need to consume packet
[rtsp @ 0x55def0b00ac0] RTP: missed 10 packets
Assertion desc failed at src/libswscale/swscale_internal.h:764
Aborted (core dumped)