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• flac : Fix channel order for mono files.

  28 juin 2014, par Erik de Castro Lopo

  flac : Fix channel order for mono files.
  * The default channel mask for mono files was 0x0001 (front left) but it
  
    makes more sense to use 0x0004 (front center) for such files.
  * Also FLAC will accept not only mono WAV files with 0x0001 mask, but also
  
    with 0x0002 (requested at https://sourceforge.net/p/flac/bugs/390/)
  
    and 0x0004 (e.g. SoX creates mono files with this mask).
  * The comment about channel support was updated.
  * The error message
  
       "Use —channel-map=none option to store channels in current order ; FLAC files
  
       must also be decoded with —channel-map=none to restore correct order."
  
    is misleading : FLAC never changes the order of channels.
  
    Decoding with this options also sets the channel mask of the resulting WAV
  
    file to 0. Without this option the mask is equal to the value of
  
    WAVEFORMATEXTENSIBLE_CHANNEL_MASK tag.
  Patch-from : lvqcl <lvqcl.mail@gmail.com>
  

  • [DH] src/flac/decode.c
  • [DH] src/flac/encode.c

• Notes on Linux for Dreamcast

  23 février 2011, par Multimedia Mike — Sega Dreamcast, VP8

  I wanted to write down some notes about compiling Linux on Dreamcast (which I have yet to follow through to success). But before I do, allow me to follow up on my last post where I got Google’s libvpx library decoding VP8 video on the DC. Remember when I said the graphics hardware could only process variations of RGB color formats ? I was mistaken. Reading over some old documentation, I noticed that the DC’s PowerVR hardware can also handle packed YUV textures (UYVY, specifically) :

  
  
  

  The video looks pretty sharp in the small photo. Up close, less so, due to the low resolution and high quantization of the test vector combined with the naive chroma upscaling. For the curious, the grey box surrounding the image highlights the 256-square texture that the video frame gets plotted on. Texture dimensions have to be powers of 2.

  Notes on Linux for Dreamcast
  I’ve occasionally dabbled with Linux on my Dreamcast. There’s an ancient (circa 2001) distro based around a build of kernel 2.4.5 out there. But I wanted to try to get something more current compiled. Thus far, I have figured out how to cross compile kernels pretty handily but have been unsuccessful in making them run.

  Here are notes are the compilation portion :
  

  • kernel.org provides a very useful set of cross compiling toolchains
  • get the gcc 4.5.1 cross toolchain for SH-4 (the gcc 4.3.3 one won’t work because the binutils is too old ; it will fail to assemble certain instructions as described in this post)
  • working off of Linux kernel 2.6.37, edit the top-level Makefile ; find the ARCH and CROSS_COMPILE variables and set appropriately :

    ARCH ?= sh
    CROSS_COMPILE ?= /path/to/gcc-4.5.1-nolibc/sh4-linux/bin/sh4-linux-
    

  • $ make dreamcast_defconfig
  • $ make menuconfig ... if any changes to the default configuration are desired
  • manually edit arch/sh/Makefile, changing :

    cflags-$(CONFIG_CPU_SH4) := $(call cc-option,-m4,) \
            $(call cc-option,-mno-implicit-fp,-m4-nofpu)
    

    to :

    cflags-$(CONFIG_CPU_SH4) := $(call cc-option,-m4,) \
            $(call cc-option,-mno-implicit-fp)
    

    I.e., remove the '-m4-nofpu' option. According to the gcc man page, this will "Generate code for the SH4 without a floating-point unit." Why this is a default is a mystery since the DC’s SH-4 has an FPU and compilation fails when enabling this option.

  • On that note, I was always under the impression that the DC sported an SH-4 CPU with the model number SH7750. According to this LinuxSH wiki page as well as the Linux kernel help, it actually has an SH7091 variant. This photo of the physical DC hardware corroborates the model number.
  • $ make ... to build a Linux kernel for the Sega Dreamcast

  Running
  So I can compile the kernel but running the kernel (the resulting vmlinux ELF file) gives me trouble. The default kernel ELF file reports an entry point of 0x8c002000. Attempting to upload this through the serial uploading facility I have available to me triggers a system reset almost immediately, probably because that’s the same place that the bootloader calls home. I have attempted to alter the starting address via ’make menuconfig’ -> System type -> Memory management options -> Physical memory start address. This allows the upload to complete but it still does not run. It’s worth noting that the 2.4.5 vmlinux file from the old distribution can be executed when uploaded through the serial loader, and it begins at 0x8c210000.

• unable to successfully close ffmpeg stream in node.js

  25 septembre 2022, par K. Russell Smith

  i'm trying to write a node video app that generates frames using the canvas api (via node-canvas, the project's only npm dependancy right now), and writes it to ffmpeg via a stream to generate a video :

  


  const { createCanvas } = require('canvas');
const { spawn } = require('child_process');
const fs = require('fs');
const canvas = createCanvas(1280, 720);

const ffmpeg = spawn('ffmpeg', [
    '-y',
    '-f', 'rawVideo',
    '-vcodec', 'rawVideo',
    '-pix_fmt', 'rgb24',
    '-s', `${ canvas.width }x${ canvas.height }`,
    '-r', '40',
    '-i', '-', '-f', 'mp4',
    '-q:v', '5',
    '-an', '-vcodec', 'mpeg4', 'output.mp4',
]);

const ctx = canvas.getContext('2d');
ctx.font = '30px Prime';
ctx.fillStyle = 'blue';
ctx.textAlign = 'center';
ctx.textBaseline = 'middle';
ctx.fillText('Hello Canvas', canvas.width / 2, canvas.height / 2);

for (let i = 0; i < 250; ++i)
{
    console.log(i);
    ffmpeg.stdin.write(Buffer.from(ctx.getImageData(0, 0, canvas.width, canvas.height).data));
}
ffmpeg.stdin.end();


  


  unfortunately, when i run it, the program throws this after writing the frames :

  


  node:events:368
      throw er; // Unhandled 'error' event
      ^

Error: write EPIPE
    at WriteWrap.onWriteComplete [as oncomplete] (node:internal/stream_base_commons:98:16)
Emitted 'error' event on Socket instance at:
    at emitErrorNT (node:internal/streams/destroy:164:8)
    at emitErrorCloseNT (node:internal/streams/destroy:129:3)
    at processTicksAndRejections (node:internal/process/task_queues:83:21) {
  errno: -32,
  code: 'EPIPE',
  syscall: 'write'
}

Node.js v17.1.0


  


  what am i doing wrong ?