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• lavu/tx : add an RDFT implementation

  21 janvier 2022, par Lynne

  lavu/tx : add an RDFT implementation
  RDFTs are full of conventions that vary between implementations.
  
  What I've gone for here is what's most common between
  
  both fftw, avcodec's rdft and what we use, the equivalent of
  
  which is DFT_R2C for forward and IDFT_C2R for inverse. The
  
  other 2 conventions (IDFT_R2C and DFT_C2R) were not used at
  
  all in our code, and their names are also not appropriate.
  
  If there's a use for either, we can easily add a flag which
  
  would just flip the sign on one exptab.
  For some unknown reason, possibly to allow reusing FFT's exp tables,
  
  av_rdft's C2R output is 0.5x lower than what it should be to ensure
  
  a proper back-and-forth conversion.
  
  This code outputs its real samples at the correct level, which
  
  matches FFTW's level, and allows the user to change the level
  
  and insert arbitrary multiplies for free by setting the scale option.
  

  • [DH] libavutil/tx.c
  • [DH] libavutil/tx.h
  • [DH] libavutil/tx_template.c

• FFmpeg scale and watermark filters with VAAP gives error "Cannot allocate memory." [closed]

  8 février 2024, par Diz-X

  I'm attempting to transcode any uploaded video on our website into H.264 using an ARC GPU (VAAPI). While I've achieved functionality, ffmpeg crashes after a certain period, displaying the error message : "Error while filtering : Cannot allocate memory."

  


  The following is the ffmpeg command is used transcode videos to H.264 :

  


  


  ffmpeg -hwaccel vaapi -hwaccel_output_format vaapi -vaapi_device /dev/dri/renderD129 -y -i '/Media/001.mp4' -codec:v h264_vaapi -movflags +faststart -f mp4 -b:v 500k -maxrate 1000k -bufsize 500k -vf "movie=/Watermarks/video-watermark.png,hwupload [watermark] ; [in] scale_vaapi=trunc(iw/2)*2:trunc(ih/2)*2 [scale] ; [scale][watermark] overlay_vaapi=main_w-overlay_w:main_h-overlay_h [out]" -an -pass 1 -passlogfile /tmp/91f13b11b0ccd5195b588fb204da6626 -map_metadata -1 /dev/null

  


  


  We ensure that the video is scaled to the appropriate video dimensions expected by H.264 codec , we use the "scale_vaapi=trunc(iw/2)*2:trunc(ih/2)*2" filter for this. We also apply a watermark to the video using the "overlay_vaapi=main_w-overlay_w:main_h-overlay_h" filter.

  


  If I omit the ",hwupload" after the "movie=" statement, I encounter the following error : "Impossible to convert between the formats supported by the filter 'Parsed_movie_0' and the filter 'auto_scale_0'."

  


  The "-filter-complex" results in the identical error : "Error while filtering : Cannot allocate memory.".

  


  Does anyone have insights on how to enable hardware-accelerated transcoding for this ?

  


• Revisiting Nosefart and Discovering GME

  30 mai 2011, par Multimedia Mike — Game Hacking

  I found the following screenshot buried deep in an old directory structure of mine :

  
  
  

  I tried to recall how this screenshot came to exist. Had I actually created a functional KDE frontend to Nosefart yet neglected to release it ? I think it’s more likely that I used some designer tool (possibly KDevelop) to prototype a frontend. This would have been sometime in 2000.

  However, this screenshot prompted me to revisit Nosefart.

  Nosefart Background
  Nosefart is a program that can play Nintendo Sound Format (NSF) files. NSF files are files containing components that were surgically separated from Nintendo Entertainment System (NES) ROM dumps. These components contain the music playback engines for various games. An NSF player is a stripped down emulation system that can simulate the NES6502 CPU along with the custom hardware (2 square waves, 1 triangle wave, 1 noise generator, and 1 limited digital channel).

  Nosefart was written by Matt Conte and eventually imported into a Sourceforge project, though it has not seen any development since then. The distribution contains standalone command line players for Linux and DOS, a GTK frontend for the Linux command line version, and plugins for Winamp, XMMS, and CL-Amp.

  The Sourceforge project page notes that Nosefart is also part of XBMC. Let the record show that Nosefart is also incorporated into xine (I did that in 2002, I think).

  Upgrading the API
  When I tried running the command line version of Nosefart under Linux, I hit hard against the legacy audio API : OSS. Remember that ?

  In fairly short order, I was able to upgrade the CL program to use PulseAudio. The program is not especially sophisticated. It’s a single-threaded affair which checks for a keypress, processes an audio frame, and sends the frame out to the OSS file interface. All that was needed was to rewrite open_hardware() and close_hardware() for PA and then replace the write statement in play(). The only quirk that stood out is that including <pulse/pulseaudio.h> is insufficient for programming PA’s simple API. <pulse/simple.h> must be included separately.

  For extra credit, I adapted the program to ALSA. The program uses the most simplistic audio output API possible — just keep filling a buffer and sending it out to the DAC.

  Discovering GME
  I’m not sure what to do with the the program now since, during my research to attempt to bring Nosefart up to date, I became aware of a software library named Game Music Emu, or GME. It’s a pure C++ library that can essentially play any classic video game format you can possible name. Wow. A lot can happen in 10 years when you’re not paying attention.

  It’s such a well-written library that I didn’t need any tutorial or documentation to come up to speed. Just a quick read of the main gme.h header library enabled me in short order to whip up a quick C program that could play NSF and SPC files. Path of least resistance : Client program asks library to open a hardcoded file, synthesize 10 seconds of audio, and dump it into a file ; ask the FLAC command line program to transcode raw data to .flac file ; use ffplay to verify the results.

  I might develop some other uses for this library.