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• Naive Sorenson Video 1 Encoder

  12 septembre 2010, par Multimedia Mike — General

  (Yes, the word is “naive” — or rather, “naïve” — not “native”. People always try to correct me when I use the word. Indeed, it should actually be written with 2 dots over the ‘i’ but who has a keyboard that can easily do that ?)

  At the most primitive level, programming a video encoder is about writing out a sequence of bits that the corresponding video decoder will understand. It’s sort of like creating a program — represented as a stream of opcodes — that will run on a given microprocessor or virtual machine. In fact, reading a video codec bitstream specification will reveal a lot of terminology along the lines of “transmitting information to the decoder” or “signaling the decoder to do xyz.”

  Creating a good encoder that will deliver decent quality at a reasonable bitrate is difficult. Creating a naive encoder that produces a technically compliant bitstream, not so much.

  
  
  

  When I wrote an FFmpeg encoder for Sorenson Video 1 (SVQ1), the first step was to just create a minimally compliant bitstream. The coarsest encoding mode that SVQ1 allows is to encode the average (mean) of each 16×16 block of samples. So I created an encoder that just encoded the mean of each block. Apple’s QuickTime Player was able to play the resulting video in all of its blocky glory. The result rather reminds me of the Super Nintendo’s mosaic effect.

  Level 5 blocks (mean-only 16×16 encoding) :
  

  
  
  

  Level 3 blocks (mean-only 8×8 encoding) :
  

  
  
  

  It’s one thing for your own decoder (in this case, FFmpeg’s own decoder) to be able to decode the data. The big test is whether the official decoder (in this case, Apple QuickTime Player) can decode the file.

  
  
  

  Now that’s a good feeling. After establishing that sort of baseline, it’s possible to adapt more and more features of the codec.

• png_parser : Fix parsing on big endian

  18 décembre 2013, par Martin Storsjö

  png_parser : Fix parsing on big endian
  Since pc.state is populated by shifting in from the end of the
  
  32 bit word, the content within pc.state is already in native endian
  
  and should not be read with the AV_RL,B functions.
  This was already done correctly for state64 above.
  This fixes the fate-corepng test on big endian.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavcodec/png_parser.c

• Adding mp3 metadata with space in ffmpeg using bash [duplicate]

  15 septembre 2019, par ctrlnot

  This question already has an answer here :

  • When to wrap quotes around a shell variable ?
    
    5 answers
    

  I have this bash script on downloading youtube videos then convert it to mp3 using youtube-dl and ffmpeg.

  #!/bin/bash
  
  
  
  ytlink=""
  
  outputFileName=""
  
  title=""
  
  artist=""
  
  album=""
  
  
  
  while getopts l:o:t:r:b: flag; do
  
    case "${flag}" in
  
      l) ytlink="${OPTARG}";;
  
      o) outputFileName="${OPTARG}";;
  
      t) title="${OPTARG}";;
  
      r) artist="${OPTARG}";;
  
      b) album="${OPTARG}";;
  
    esac
  
  done
  
  
  
  youtube-dl "$ytlink" --add-metadata --extract-audio --audio-format mp3 --output "temp.%(ext)s"
  
  
  
  tempFilename="temp.mp3"
  
  outputFileName="$outputFileName.mp3"
  
  
  
  args+=("-i" "$tempFilename" "-metadata" "title='$title'" "-metadata" "artist='$artist'" "-metadata" "album='$album'" "-metadata" "comment=Source:$ytlink")
  
  ffmpeg -loglevel debug ${args[@]} -acodec copy "$outputFileName"
  
  rm "$tempFilename"

  This script is fine if I have one word title/artist/album. However, if I have a space, ffmpeg interprets each word before space as another parameter. This is how I use this on command line :

  ./yttomp3.sh -l "https://www.youtube.com/watch?v=KwQnSHAilOQ" -o "Lee - Autumn Day" -t "Autumn Day" -r "Lee" -b "(Free) Lo-fi Type Beat - Autumn Day"

  The debug output of ffmpeg :

  Splitting the commandline.
  
  Reading option '-loglevel' ... matched as option 'loglevel' (set logging level) with argument 'debug'.
  
  Reading option '-i' ... matched as input url with argument 'temp.mp3'.
  
  Reading option '-metadata' ... matched as option 'metadata' (add metadata) with argument 'title='Autumn'.
  
  Reading option 'Day'' ... matched as output url.
  
  Reading option '-metadata' ... matched as option 'metadata' (add metadata) with argument 'artist='Lee''.
  
  Reading option '-metadata' ... matched as option 'metadata' (add metadata) with argument 'album='(Free)'.
  
  Reading option 'Lo-fi' ... matched as output url.
  
  Reading option 'Type' ... matched as output url.
  
  Reading option 'Beat' ... matched as output url.
  
  Reading option '-' ... matched as output url.
  
  Reading option 'Autumn' ... matched as output url.
  
  Reading option 'Day'' ... matched as output url.
  
  Reading option '-metadata' ... matched as option 'metadata' (add metadata) with argument 'comment=Source:https://www.youtube.com/watch?v=KwQnSHAilOQ'.
  
  Reading option '-acodec' ... matched as option 'acodec' (force audio codec ('copy' to copy stream)) with argument 'copy'.
  
  Reading option 'Lee - Autumn Day.mp3' ... matched as output url.
  
  Finished splitting the commandline.

  I tried enclosing the arguments to quotes on the script but it’s still not working. How should I deal with this ? Thanks.