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• Further SMC Encoding Work

  25 août 2011, par Multimedia Mike — General

  Sometimes, when I don’t feel like doing anything else, I look at that Apple SMC video encoder again.

  8-bit Encoding
  When I last worked on the encoder, I couldn’t get the 8-color mode working correctly, even though the similar 2- and 4-color modes were working fine. I chalked the problem up to the extreme weirdness in the packing method unique to the 8-color mode. Remarkably, I had that logic correct the first time around. The real problem turned out to be with the 8-color cache and it was due to the vagaries of 64-bit math in C. Bit shifting an unsigned 8-bit quantity implicitly results in a signed 32-bit quantity, or so I discovered.

  Anyway, the 8-color encoding works correctly, thus shaving a few more bytes off the encoding size.

  Encoding Scheme Oddities
  The next step is to encode runs of data. This is where I noticed some algorithmic oddities in the scheme that I never really noticed before. There are 1-, 2-, 4-, 8-, and 16-color modes. Each mode allows encoding from 1-256 blocks of that same encoding. For example, the byte sequence :

    0x62 0x45
  

  Specifies that the next 3 4×4 blocks are encoded with single-color mode (of byte 0×62, high nibble is encoding mode and low nibble is count-1 blocks) and the palette color to be used is 0×45. Further, opcode 0×70 is the same except the following byte allows for specifying more than 16 (i.e., up to 256) blocks shall be encoded in the same matter. In light of this repeat functionality being built into the rendering opcodes, I’m puzzled by the existence of the repeat block opcodes. There are opcodes to repeat the prior block up to 256 times, and there are opcodes to repeat the prior pair of blocks up to 256 times.

  So my quandary is : What would the repeat opcodes be used for ? I hacked the FFmpeg / Libav SMC decoder to output a histogram of which opcodes are used. The repeat pair opcodes are never seen. However, the single-repeat opcodes are used a few times.

  Puzzle Solved ?
  I’m glad I wrote this post. Just as I was about to hit “Publish”, I think I figured it out. I haven’t mentioned the skip opcodes yet– there are opcodes that specify that 1-256 4×4 blocks are unchanged from the previous frame. Conceivably, a block could be unchanged from the previous frame and then repeated 1-256 times from there.

  That’s something I hadn’t thought of up to this point for my proposed algorithm and will require a little more work.

  Further reading

  • My first entry regarding my toy SMC encoder

• ffmpeg, -shortest does not work when overlaying PNG sequence on a still

  27 août 2014, par Aviator Addis

  How do you make this work ?

  ffmpeg -loop 1 -i emma.jpg -r 29.97 -i source\source_%%05d.png -filter_complex overlay -r 29.97 -pix_fmt yuv420p -y -shortest sample_source.mp4

  It seems the -shortest option does not work and it just keeps encoding with no stop on the last frame. I’m using the latest static 8-27-2014 64 bit build on windows 8.1 If I assigned -t value it will stop at the specified length, but I need it’s output length set to whatever the sequence might happen to be (at it will vary).

• I have pip installed pydub but still didn't work

  1er mai 2023, par Dom807

  After I had pip installed pydub and SpeechRecognition, I still can't make the program run successfully although I extracted the files from ffmpeg and specified the folder name bin in the corresponding directory. I tried to find solutions to solve the problem but it sill didn't work after I followed the steps clearly from the web. May I ask what is the good way to read .wav files using pydub AudioSegment ?

  


    Warning (from warnings module):
      File "C:\Python38\lib\site-packages\pydub\utils.py", line 171
        warn("Couldn't find ffmpeg or avconv - defaulting to ffmpeg, but may not work", RuntimeWarning)
    RuntimeWarning: Couldn't find ffmpeg or avconv - defaulting to ffmpeg, but may not work