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• Survey of CD Image Formats

  30 avril 2013, par Multimedia Mike — General

  In the course of exploring and analyzing the impressive library of CD images curated at the Internet Archive’s Shareware CD collection, one encounters a wealth of methods for copying a complete CD image onto other media for transport. In researching the formats, I have found that many of them are native to various binary, proprietary CD programs that operate under Windows. Since I have an interest in interpreting these image formats and I would also like to do so outside of Windows, I thought to conduct a survey to determine if enough information exists to write processing tools of my own.

  Remember from my Grand Unified Theory of Compact Disc that CDs, from a high enough level of software abstraction, are just strings of 2352-byte sectors broken up into tracks. The difference among various types of CDs comes down to the specific meaning of these 2352 bytes.

  Most imaging formats rip these strings of sectors into a giant file and then record some metadata information about the tracks and sectors.

  ISO
  This is perhaps the most common method for storing CD images. It’s generally only applicable to data CD-ROMs. File images generally end with a .iso extension. This refers to ISO-9660 which is the standard CD filesystem.

  Sometimes, disc images ripped from other types of discs (like Xbox/360 or GameCube discs) bear the extension .iso, which is a bit of a misnomer since they aren’t formatted using the ISO-9660 filesystem. But the extension sort of stuck.

  BIN / CUE
  I see the BIN & CUE file format combination quite frequently. Reportedly, a program named CDRWIN deployed this format first. This format can handle a mixed mode CD (e.g., starts with a data track and is followed by a series of audio tracks), whereas ISO can only handle the data track. The BIN file contains the raw data while the CUE file is a text file that defines how the BIN file is formatted (how many bytes in a sector, how many sectors to each individual track).

  CDI
  This originates from a program called DiscJuggler. This is extremely prevalent in the Sega Dreamcast hobbyist community for some reason. I studied the raw hex dumps of some sample CDI files but there was no obvious data (mostly 0s). There is an open source utility called cdi2iso which is able to extract an ISO image from a CDI file. The program’s source clued me in that the metadata is actually sitting at the end of the image file. This makes sense when you consider how a ripping program needs to operate– copy tracks, sector by sector, and then do something with the metadata after the fact. Options include : 1) Write metadata at the end of the file (as seen here) ; 2) write metadata into a separate file (seen in other formats on this list) ; 3) write the data at the beginning of the file which would require a full rewrite of the entire (usually large) image file (I haven’t seen this yet).

  Anyway, I believe I have enough information to write a program that can interpret a CDI file. The reason this format is favored for Dreamcast disc images is likely due to the extreme weirdness of Dreamcast discs (it’s complicated, but eventually fits into my Grand Unified Theory of CDs, if you look at it from a high level).

  MDF / MDS
  MDF and MDS pairs come from a program called Alcohol 120%. The MDF file has the data while the MDS file contains the metadata. The metadata is in an opaque binary format, though. Thankfully, the Wikipedia page links to a description of the format. That’s another image format down.

  CCD / SUB / IMG
  The CloneCD Control File is one I just ran across today thanks to a new image posted at the IA Shareware Archive (see Super Duke Volume 2). I haven’t found any definitive documentation on this, but it also doesn’t seen too complicated. The .ccd file is a text file that is pretty self-explanatory. The sample linked above, however, only has a .ccd file and a .sub file. I’m led to believe that the .sub file contains subchannel information while a .img file is supposed to contain the binary data. So this rip might be incomplete (nope, the .img file is on the page, in the sidebar ; thanks to Phil in the comments for pointing this out). The .sub file is a bit short compared to the Archive’s description of the disc’s contents (only about 4.6 MB of data) and when I briefly scrolled through, it didn’t look like it contains any real computer data. So it probably is just the disc’s subchannel data (something I glossed over in my Grand Unified Theory).

  CSO
  I have dealt with the CISO (compressed ISO) format before. It’s basically the same as a .iso file described above except that each individual 2048-byte data sector is compressed using zlib. The format boasts up to 9 compression levels, which shouldn’t be a big surprise since that correlates to zlib’s own compression tiers.

  Others
  Wikipedia has a category for optical disc image formats. Of course, there are numerous others. However, I haven’t encountered them in the wild for the purpose of broad image distribution.

• FFMPEG H264 with custom overlay per frame

  4 octobre 2020, par La bla bla

  We have a stream that is stored in the cloud (Amazon S3) as individual H264 frames. The frames are stored as framexxxxxx.264, the numbering doesn't start from 0 but rather from some larger number, say 1000 (so, frame001000.264)

  


  The goal is to create a mp4 clip which is either timelapse or just faster for inspection and other checking (much faster, compressing around 3 hours of video down to < 20 minutes), this also requires we overlay the frame number (the filename) on the frame itself

  &#xA;

  At first I was creating a timelapse by pulling from S3 only the keyframes (i-frames ? still rather new to codecs & stuff) and overlaying the filename on them and saving as png (which probably isn't needed, but that's what I did) using (this command is used inside a python script)

  &#xA;

  ffmpeg -y -i {h264_name} -vf \"scale=1920:-1, 
drawtext=fontfile=/usr/share/fonts/truetype/ubuntu-font-family/Ubuntu-B.ttf:fontsize=34:text={txt}:fontcolor=white:x=50:y=50:bordercolor=black:borderw=2\" 
-c:a copy -pix_fmt yuv420p {basename}.png


  &#xA;

  after this I combined all the frames by using python to convert the lowest numbered frame to 0.png and incrementing (so it would be continuous, because I only used keyframes the numbers originally weren't sequential) and running

  &#xA;

  ffmpeg -y -f image2 -i %d.png -r {self.params.fps} -vcodec libx264 -crf {self.params.crf} -pix_fmt yuv420p {out_file}


  &#xA;

  and this worked great, but the difference between keyframes was too long to allow for proper inspection

  &#xA;

  so now for the question(s)

  &#xA;

  since I know frames that are not keyframes (p-frames ?) can't be used alone by ffmpeg, the method of overlaying the file name and converting it to png (or keep as h264, same thing) won't work, or at least, I couldn't find a way for it to work, maybe there's a way to specify a frame's keyframe ?, how can one overlay the filename (and not the frame number as shown here for example)

  &#xA;

  Also, is it possible to skip some p-frames between the keyframes ? (so if a keyframe is every 30 frames, we would take a keyframe, a frame 15 frames later, and next another keyframe)

  &#xA;

  I thought about using ffmpeg's pipe option to feed it with the files as they're being downloaded, but I'm not sure if I can specify drawtext this way

  &#xA;

  Also, if there's another alternative that can achieve that (at first I was converting to png, using python and OpenCV to add the filename and then merging the pngs to mp4, but then I found drawtext can do that in a single command so I used it)

  &#xA;

• ffmpeg : add a data size threshold for muxing queue size

  15 octobre 2020, par Jan Ekström

  ffmpeg : add a data size threshold for muxing queue size
  This way the old max queue size limit based behavior for streams
  
  where each individual packet is large is kept, while for smaller
  
  streams more packets can be buffered (current default is at 50
  
  megabytes per stream).
  For some explanation, by default ffmpeg copies packets from before
  
  the appointed seek point/start time and puts them into the local
  
  muxing queue. Before, it getting utilized was much less likely
  
  since as soon as the filter chain was initialized, the encoder
  
  (and thus output stream) was also initialized.
  Now, since we will be pushing the encoder initialization to when the
  
  first AVFrame is decoded and filtered - which only happens after
  
  the exact seek point is hit as packets are ignored until then -
  
  this queue will be seeing much more usage.
  In more layman's terms, this attempts to fix cases such as where :
  
   seek point ends up being 5 seconds before requested time.
  
   audio is set to copy, and thus immediately begins filling the
  
    muxing queue.
  
   video is being encoded, and thus all received packets are skipped
  
    until the requested time is hit.
  

  • [DH] doc/ffmpeg.texi
  • [DH] fftools/ffmpeg.c
  • [DH] fftools/ffmpeg.h
  • [DH] fftools/ffmpeg_opt.c