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• Cannot find yasm even though I have installed it

  20 juillet 2017, par zhen lee

  I got a strange problem. I tried to install x264. When run sudo ./configure —enable-shared,
  it gave :

  Found no assembler
  Minimum version is yasm-0.7.0
  If you really want to compile without asm, configure with —disable-asm.

  But I already installed yasm-0.7.0 ,to prove that ,i run yasm —version,it gave :

  *yasm 0.7.0.2066
  Compiled on May 8 2012.
  Copyright (c) 2001-2008 Peter Johnson and other Yasm developers.
  Run yasm —license for licensing overview and summary.*

  I install yasm to /usr/local/yasm,
  Why can it not find yasm ?

• 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.

• ffmpeg : simple RTMP streaming over LAN

  30 mars 2013, par sajad

  I am trying to launch up a rtmp transcoder server using ffmpeg ; that receives udp MPEG-TS streams as input, transcodes it ; and generates an rtmp output to a URL, that can be accessed by users to receive and play the rtmp stream. All these are expected to be performed in a LAN and the output be accessed by all users.

  1) First I don't know where the URL should point to. Is it enought to specify the IP of the system and some optional port ? Is it neccessary that a program should be listening on that port ?

  2) How I can play the stream on the URL ?

  I use a linux ubuntu machine whith IP=10.1.1.229 and I want to transcode multicast stream on this URL : udp://@224.10.1.1:2001.

  here is the command used to transcode input stream and generate rtmp url "rtmp ://10.1.1.229:2020".

  ffmpeg -y -f mpegts -i "udp://@224.10.1.1:2001" -re -vcodec libx264 -maxrate 700k -r 25 -s 640x360 -deinterlace -acodec libfaac -ab 64k -ac 1 -ar 44100 -f flv "rtmp://10.1.1.229:2020"

  and here is the command by which I am trying to play rtmp stream :

  ffplay rtmp://10.1.1.229:2020

  Any guidance would be helpfull. Thank you.