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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.

• what is wrong with this ffmpeg command ?

  16 juillet 2013, par kheya

  I am trying to convert 3gp movie to H264 video (mp4)
  This is what I am using :

  ffmpeg -i file8.3gp -vcodec libx264 -preset slow -vf scale="720:trunc(ow/a/2)*2" -threads 0 -acodec libvo_aacenc -b:a 128k "file8.mp4"

  The problem is original file is 28kb but after conversion I get 155kb mp4 file
  Why is the file so bloated - is that because of the size or some other option ?

  Here is what I see on 3gp input file : NOTE THE BIT RATE IS 46 KB/S

  libavutil      52. 39.100 / 52. 39.100
  
    libavcodec     55. 18.102 / 55. 18.102
  
    libavformat    55. 12.102 / 55. 12.102
  
    libavdevice    55.  3.100 / 55.  3.100
  
    libavfilter     3. 80.101 /  3. 80.101
  
    libswscale      2.  3.100 /  2.  3.100
  
    libswresample   0. 17.102 /  0. 17.102
  
    libpostproc    52.  3.100 / 52.  3.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'file8.3gp':
  
    Metadata:
  
      major_brand     : 3gp5
  
      minor_version   : 256
  
      compatible_brands: 3gp53gp4
  
      creation_time   : 2005-10-28 17:36:40
  
    Duration: 00:00:04.93, start: 0.000000, bitrate: 46 kb/s
  
      Stream #0:0(eng): Audio: amr_nb (samr / 0x726D6173), 8000 Hz, mono, flt, 8 k
  
  b/s
  
      Metadata:
  
        creation_time   : 2005-10-28 17:36:40
  
        handler_name    : Apple Sound Media Handler
  
      Stream #0:1(eng): Video: mpeg4 (Simple Profile) (mp4v / 0x7634706D), yuv420p
  
  , 176x144 [SAR 1:1 DAR 11:9], 35 kb/s, 15 fps, 15 tbr, 600 tbn, 1k tbc
  
      Metadata:
  
        creation_time   : 2005-10-28 17:36:40
  
        handler_name    : Apple Video Media Handler

  Here is what I see on mp4 output file : NOTE THE BIT RATE IS 243 KB/S

  libavutil      52. 39.100 / 52. 39.100
  
    libavcodec     55. 18.102 / 55. 18.102
  
    libavformat    55. 12.102 / 55. 12.102
  
    libavdevice    55.  3.100 / 55.  3.100
  
    libavfilter     3. 80.101 /  3. 80.101
  
    libswscale      2.  3.100 /  2.  3.100
  
    libswresample   0. 17.102 /  0. 17.102
  
    libpostproc    52.  3.100 / 52.  3.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'file8.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf55.12.102
  
    Duration: 00:00:05.20, start: 0.200000, bitrate: 243 kb/s
  
      Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 720x588 [
  
  SAR 539:540 DAR 11:9], 240 kb/s, 15 fps, 15 tbr, 15360 tbn, 30 tbc
  
      Metadata:
  
        handler_name    : VideoHandler
  
      Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 8000 Hz, mono, fltp, 10 kb
  
  /s
  
      Metadata:
  
        handler_name    : SoundHandler
  
  At least one output file must be specified

• MKV to MP4 command on MacOS [closed]

  28 février 2023, par Zakary Morton

  First time attempting anything more in-depth via Terminal, and I think I've sorted out the proper coding for my conversion. What I'd like to know/double-check are : 1) Is there a way to compress/control the size of the output file ? ; 2) Can I run this from a top-level folder and convert all videos under it rather than just next level down ? ; 3) Can I automate this somehow ? ; 4) Am I converting these in a way that will make them playable on apple tv ? ; 4) And finally, like, did I do it right ? Is there a simpler way to write this ?

  


  Here's the command :

  


  


  mkdir output
for f in *.mkv ; do ffmpeg -i "$f" -c:v libx265 -c:a aac -b:a 128k -preset : veryfast -tag:v hvc1 "output/$f%mkvmp4" ;done

  


  


  Seems to be running ok, but not sure how long its meant to take to complete. Thanks for your inside from a newb