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• MediaStream to C++ data type conversion

  20 juillet 2016, par Mohammad Abu Musa

  I am sending a video and audio stream to C++ from Google Chrome, I am not sure how to cast the data.

  What is the data type of this and how do I convert it to C++ ?

  videoStream.getVideoTracks()[0]

  I want to build ffmpeg encoder using C++ but I can not figure out how to cast this type ?

  I was also wondering if there is method to build a test case similar to this data type ?

• Dreamcast Track Sizes

  1er mars 2015, par Multimedia Mike — Sega Dreamcast

  I’ve been playing around with Sega Dreamcast discs lately. Not playing the games on the DC discs, of course, just studying their structure. To review, the Sega Dreamcast game console used special optical discs named GD-ROMs, where the GD stands for “gigadisc”. They are capable of holding about 1 gigabyte of data.

  You know what’s weird about these discs ? Each one manages to actually store a gigabyte of data. Each disc has a CD portion and a GD portion. The CD portion occupies the first 45000 sectors and can be read in any standard CD drive. This area is divided between a brief data track and a brief (usually) audio track.

  The GD region starts at sector 45000. Sometimes, it’s just one humongous data track that consumes the entire GD region. More often, however, the data track is split between the first track and the last track in the region and there are 1 or more audio tracks in between. But the weird thing is, the GD region is always full. I made a study of it (click for a larger, interactive graph) :

  
  
  

  Some discs put special data or audio bonuses in the CD region for players to discover. But every disc manages to fill out the GD region. I checked up on a lot of those audio tracks that divide the GD data and they’re legitimate music tracks. So what’s the motivation ? Why would the data track be split in 2 pieces like that ?

  I eventually realized that I probably answered this question in this blog post from 4 years ago. The read speed from the outside of an optical disc is higher than the inside of the same disc. When I inspect the outer data tracks of some of these discs, sure enough, there seem to be timing-sensitive multimedia FMV files living on the outer stretches.

  One day, I’ll write a utility to take apart the split ISO-9660 filesystem offset from a weird sector.

• ffmpeg - extract timecode start metadata from tmcd track to a drawtext filter

  3 mars 2015, par mwjb

  I have a Quicktime file with a timecode track. I’m encoding it to a new video codec and would like to burnin the timecode from timecode track. Setting the timecode manually isn’t an option as this will be used for many files with unique starting timecodes.

  This is the current work-in-progress ffmpeg command. Obviously I need to find a way to extract the metadate:timecode value and have this start the timecode count instead of the manual entry seen below :

  ffmpeg -i infile.mov -y -c:v mjpeg -qscale:v 4 -vendor ap10 -pix_fmt yuvj422p -s 1280x720 -vf drawtext="fontfile=thefont.ttf: timecode='01\:00\:00\:00': rate=24: fontsize=40: fontcolor=white: boxcolor=black: box=1: x=1700: y=80" outfile.mov

  The Timecode metadata is there in the Stream #0:1 track, as read by ffmpeg :

  ffmpeg version 2.5.2 Copyright (c) 2000-2014 the FFmpeg developers
  
    built on Jan  1 2015 20:24:48 with llvm-gcc 4.2.1 (LLVM build 2336.11.00)
  
  configuration: --prefix=/Volumes/tempdisk/sw --as=yasm --enable-gpl --enable-pthreads --disable-ffplay --disable-ffserver --disable-shared --enable-static --enable-libvpx --disable-decoder=libvpx --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libx264 --enable-libx265 --enable-libxvid --enable-zlib --enable-avfilter --enable-fontconfig --enable-libfreetype --enable-libass --enable-libutvideo --enable-filters --enable-postproc --enable-runtime-cpudetect
  
  libavutil      54. 15.100 / 54. 15.100
  
  libavcodec     56. 13.100 / 56. 13.100
  
  libavformat    56. 15.102 / 56. 15.102
  
  libavdevice    56.  3.100 / 56.  3.100
  
  libavfilter     5.  2.103 /  5.  2.103
  
  libswscale      3.  1.101 /  3.  1.101
  
  libswresample   1.  1.100 /  1.  1.100
  
  libpostproc    53.  3.100 / 53.  3.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'infile.mov':
  
    Metadata:
  
  major_brand     : qt  
  
  minor_version   : 537199360
  
  compatible_brands: qt  
  
  creation_time   : 2015-03-02 22:06:00
  
  timecode        : 06:00:00:00
  
  Duration: 00:20:00.00, start: 0.000000, bitrate: 36175 kb/s
  
  Stream #0:0(eng): Video: dnxhd (AVdn / 0x6E645641), yuv422p, 1920x1080, 36175 kb/s, 24 fps, 24 tbr, 24k tbn, 24k tbc (default)
  
  Metadata:
  
    creation_time   : 2015-03-02 22:06:00
  
    handler_name    : Apple Alias Data Handler
  
    encoder         : Avid DNxHD Codec
  
  Stream #0:1(eng): Data: none (tmcd / 0x64636D74) (default)
  
  Metadata:
  
    creation_time   : 2015-03-02 22:06:58
  
    handler_name    : Apple Alias Data Handler
  
    timecode        : 06:00:00:00

  I came across this post ffmpeg and timecode from movie metadata which appeared to be on the same sort of track as I’m on. Would certainly appreciate some guidance on this. Many Thanks.