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• ISO-9660 Compromise, Part 2 : Finding Root

  25 octobre 2021, par Multimedia Mike — General

  A long time ago, I dashed off a quick blog post with a curious finding after studying the ISO-9660 spec : The format stores multi-byte numbers in a format I termed “omni-endian”– the committee developing the format apparently couldn’t come to an agreement on this basic point regarding big- vs. little-endian encoding (I’m envisioning something along the lines of “tastes great ! … less filling !” in the committee meetings).

  I recently discovered another bit of compromise in the ISO-9660 spec : It seems that there are 2 different methods for processing the directory structure. That means it’s incumbent upon ISO-9660 creation software to fill in the data structures to support both methods, because some ISO-reading programs out there rely on one set of data structures while the rest prefer to read the other set.

  Background

  As a refresher, the “ISO” extension of an ISO file refers to the ISO-9660 specification. This is a type of read-only filesystem (i.e, the filesystem is created once and never updated after initial creation) for the purpose of storing on a read-only medium, often an optical disc (CD-ROM, DVD-ROM). The level of nostalgic interest I display for the ISO-9660 filesystem reminds me of my computer science curriculum professors from the mid-90s reminiscing about ye olden days of punchcard programming, but such is my lot. I’m probably also alone in my frustration of seeing rips of, e.g., GameCube or Xbox or 3DO games being tagged with the extension .ISO since those systems use different read-only filesystems.

  I recently fell in with an odd bunch called the eXoDOS project and was trying to help fill in a few gaps. One request was a 1994 game called Power Drive for DOS.

  
  
  

  
  

  My usual CD-ROM ripping method (for the data track) is a simple ‘dd’ command from a Linux command line to copy the string of raw sectors. However, it turned out to be unusually difficult to open the resulting ISO. A few of the the options I know of worked but most didn’t. What’s the difference ?

  Methods that work :

  • Mounting the file with the Linux iso9660 kernel module, i.e.,

    mount -t iso9660 /dev/optical-drive /mnt

    or

    mount -t iso9660 -o loop /path/to/Power-Drive.iso /mnt

  • Directory Opus
  • Windows 10 can read the filesystem when reading the physical disc
  • Windows 10 can burn the ISO image to a new CD (“right click” -> “Burn disc image”) ; this method does not modify any of the existing sectors but did append 149 additional empty sectors

  Methods that don’t work :

  • fuseiso
  • Dosbox
  • Winrar
  • 7zip
  • Daemon Tools
  • Imgburn
  • Internet Archive’s ISO lister (“View contents” on the ISO file)

  Understanding The Difference

  I think I might have a handle on why some tools are able to process this disc while most can’t. There appears to be 2 sets of data structures to describe the base of the filesystem : A root directory, and a path table. These both occur in the first substantive sector of the ISO-9660 filesystem, usually sector 16.

  A compact disc can be abstractly visualized as a long string of sectors, each one 2,352 bytes long. (See my Grand Unified Theory of Compact Disc post for deeper discussion.) A CD-ROM data track will contain 2048 bytes of data. Thus, sector 16 appears at 0x8000 of an ISO filesystem. I like the clarity of this description of the ISO-9660 spec. It shows that the path table is defined at byte 140 (little-endian ; big comes later) and location of the root directory is at byte 158. Thus, these locations generally occur at 0x808c and 0x809e.

  
  
  Primary Volume Descriptor
  

  The path table is highlighted in green and the root directory record is highlighted in red. These absolute locations are specified in sectors. So the path table is located at sector 0x12 = offset 0x9000 in the image, while the root directory record is supposed to be at sector 0x62 = 0x31000. Checking into those sectors, it turns out that the path table is valid while the root directory record is invalid. Thus, any tool that relies on the path table will be successful in interpreting the disc, while tools that attempt to recursively traverse starting from root directory record are gonna have a bad time.

  Since I was able to view the filesystem with a few different tools, I know what the root directory contains. Searching for those filenames reveals that the root directory was supposed to point to the next sector, number 0x63. So this was a bizarre off-by-1 error on the part of the ISO creation tool. Maybe. I manually corrected 0x62 -> 0x63 and that fixed the interaction with fuseiso, but not with other tools. So there may have been some other errors. Note that a quick spot-check of another, functional ISO revealed that this root directory sector is supposed to be exact, not 1-indexed.

  Upon further inspection, I noticed that, while fuseiso appeared to work with that one patch, none of the files returned correct data, and none of the directories contained anything. That’s when I noticed that ALL of the sector locations described in the various directory and file records are off by 1 !

  Further Investigation

  I have occasionally run across ISO images on the Internet Archive that return the error about not being able to read the contents when trying to “View contents” (error text : “failed to obtain file list from xyz.iso”, as seen with this ISO). Too bad I didn’t make a record of them because I would be interested to see if they have the same corruption.

  Eventually, I’ll probably be able to compile an archive of deviant ISO-9660 images. A few months ago, I was processing a large collection from IA and found a corrupted ISO which had a cycle, i.e., the subdirectory pointed to a parent directory, which caused various ISO tools to loop forever. Just one of those things that is “never supposed to happen”, so why write code to deal with it gracefully ?

  See Also

  • The disc archived at The Internet Archive
  • MobyGames Entry
  • Wikipedia Entry

  The post ISO-9660 Compromise, Part 2 : Finding Root first appeared on Breaking Eggs And Making Omelettes.

• Capture xvfb stream from docker container using webRTC [closed]

  5 septembre 2023, par HIMANSHU SAHU

  I have a windows game .exe file and running the game inside a docker container (In EC2 linux VM) using xvfb version of X server. Now I want to Capture X server stream from docker container to my local system using webRTC. What should I do for the same ?

  


  Here's my Dockerfile :

  


  FROM ubuntu:22.04

  


  #Specify a workdir, to better organize your files inside the container.

  


  WORKDIR /app

  


  #Update package lists and install required packages

  


  RUN apt-get update
RUN apt-get install -y wget software-properties-common gnupg2 winbind xvfb
RUN apt-get -qq update -y && apt-get -qq install -y —no-install-recommends \
build-essential cpp cpp-9 g++-9 gcc-9 gcc-10 g++-10 gcc-multilib gcc-mingw-w64
  
git-core
  
dkms
  
ffmpeg

  


  #Add Wine repository and install

  


  RUN dpkg —add-architecture i386
RUN mkdir -pm755 /etc/apt/keyrings
RUN wget -O /etc/apt/keyrings/winehq-archive.key https://dl.winehq.org/wine-builds/winehq.key
RUN wget -NP /etc/apt/sources.list.d/ https://dl.winehq.org/wine-builds/ubuntu/dists/jammy/winehq-jammy.sources
RUN apt-get update

  


  RUN apt-get -qq update -y && apt-get -qq install -y —no-install-recommends
  
alsa-utils
  
libasound2-dev libdbus-1-dev libfontconfig-dev libfreetype-dev libgnutls28-dev libldap-common
  
libodbc1 libv4l-0 libjpeg-dev libldap2-dev libpng-dev libtiff-dev libgl-dev libunwind-dev libxml2-dev
  
libxslt1-dev
  
libfaudio-dev
  
libmpg123-dev
  
libosmesa6-dev
  
libsdl2-dev
  
libudev-dev
  
libvkd3d-dev \
libvulkan-dev

  


  RUN apt-get -qq update -y && apt-get -qq install -y —no-install-recommends
  
ocl-icd-opencl-dev
  
bison
  
schroot
  
debootstrap
  
flex

  


  RUN apt-get -qq update -y && apt-get -qq install -y —no-install-recommends
  
libmpg123-dev:i386
  
libosmesa6-dev:i386
  
libvulkan-dev:i386
  
ocl-icd-opencl-dev:i386
  
bison:i386
  
flex:i386

  


  RUN apt-get install -y linux-firmware

  


  #Install additional packages and configure Wine

  


  RUN apt-get install —no-install-recommends -y winehq-stable winetricks cabextract

  


  RUN winetricks msxml6

  


  #Cleanup unnecessary files

  


  RUN apt-get clean
RUN rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*

  


  ENV WINEDEBUG=-d3d

  


  COPY app /root/catalyst
COPY overcooked_drm-free_20_566540 /root/overcooked_drm-free_20_566540
COPY startup.sh /root/startup.sh
RUN chmod 755 /root/startup.sh

  


  EXPOSE 9000

  


  CMD ["/root/startup.sh"]

  


  Startup.sh :

  


  # !/usr/bin/env bash

  


  sleep 1s
Xvfb :1 -screen 0 1024x768x24 &

  


  glxinfo -force-d3d9
ffmpeg -video_size 1024x768 -framerate 25 -f x11grab -i :1 -t 120 outputofscreen1.mp4 &

  


  DISPLAY=:1 wine /root/overcooked_drm-free_20_566540/Overcooked.exe -force-d3d11

  


  ---

  


  As of now I'm capturing the xserver stream using ffmpeg and storing the same in .mp4 file. Now I want to play the game on my local machine by using webRTC for connection and streaming.

  


  I have run the .exe in linux using wine and xvfb server and captured the stream using ffmpeg and stored in a .mp4 file.

  


• How to divide a live stream coming from a camera into many 60-second video clips in mp4 format with ffmpeg

  17 septembre 2020, par guidop21

  Using the following code :

  


  ffmpeg -f dshow -rtbufsize 1000M -i video = "Game Capture HD60 S (Video) (# 01)" -codec copy -map 0 -f segment -segment_time 60 -reset_timestamps 1 "C: \ Program Files (x86) \ ffmpeg \ test \ clips \ testfile_piece_% 02d.mp4 "


  


  I have the following problem :

  


  


  "Could not find tag for codec rawvideo in stream # 0, codec not
currently supported in container Could not write header for output
file # 0 (incorrect codec parameters ?) : Invalid argument"

  


  


  How can I fix it ?

  


  Thank you