emulator: video_processor
type: utility
core_classification: pure_libretro
source: "https://github.com/libretro/libretro-video-processor"
source_mirror: "https://git.libretro.com/libretro/libretro-video-processor"
upstream: "https://github.com/jaredmcneill/libretro-v4l2"
author: "Jared McNeill"
profiled_date: "2026-09-17"
source_commit: "8fe4751f0039a1b645bf750531fcfc234958a7ac"
upstream_commit: "c608ced893583e0a8a8153890f99453fd1647d53"
core_version: "0.0.2"
display_name: "Video Processor (V4L2)"
cores:
  - video_processor
systems: []

notes: |
  Capture core for V4L2 devices: a console plugged into a capture card is
  shown through the frontend so its scalers and shaders apply to the signal.
  The core opens the capture device, requests RGB24 and two mmap buffers,
  and converts each dequeued frame to RGB565 for the video callback. Audio
  comes from an ALSA capture PCM opened at 48 kHz, S16_LE, two channels, and
  is read from the frontend audio callback. There is no emulation, no state
  to serialize and no memory map.
  ref: video_processor_v4l2.c:299-419, video_processor_v4l2.c:492-529,
       video_processor_v4l2.c:531-544, video_processor_v4l2.c:554-698

  Both devices are picked from core options built in retro_set_environment.
  The video list comes from a udev enumeration of the video4linux subsystem
  filtered on the /dev/video prefix, or from a fixed /dev/video0 to
  /dev/video3 list when libudev is not compiled in. The audio list comes from
  the ALSA PCM hints whose IOID is Input and whose name starts with hw: or
  default:. These are device nodes and PCM names, not files: nothing is read
  from the system directory, no path is built and no file is opened. The
  content handed to retro_load_game is not looked at either: valid_extensions
  is NULL, need_fullpath is false and the core never declares no-content
  support, so the frontend still asks for a file whose bytes are ignored.
  ref: video_processor_v4l2.c:140-205, video_processor_v4l2.c:208-242,
       video_processor_v4l2.c:244-268, video_processor_v4l2.c:448-455

  The frame rate is the frameperiod of the active V4L2 standard and the
  pixel aspect comes from VIDIOC_CROPCAP; retro_get_region reports NTSC when
  the standard carries the NTSC bit and PAL otherwise. A device that does not
  enumerate its active standard makes retro_load_game fail.
  ref: video_processor_v4l2.c:457-480, video_processor_v4l2.c:593-617,
       video_processor_v4l2.c:728-731

  Linux only, through linux/videodev2.h. libv4l2, ALSA and libudev are each
  autodetected by the Makefile and dropped when their header is missing;
  without libv4l2 the raw ioctl path is used and the format conversion the
  library provides is lost. The GitLab CI installs the three development
  packages, and the buildbot binary for linux x86_64 links libv4l2.so.0,
  libasound.so.2 and libudev.so.1. RetroArch also compiles a diverged copy of
  this core into its own binary under cores/libretro-video-processor when
  HAVE_VIDEOPROCESSOR is set; that copy declares no-content support and adds
  capture and output mode options, and opens the same device nodes only.
  ref: video_processor_v4l2.c:45-57, Makefile:107-124

  Written by Jared McNeill in July 2016 as libretro-v4l2. The libretro fork
  carries the author's last commits, the audio batch callback and the ALSA
  overrun recovery, then the 2026 CI and dependency autodetection change; the
  original repository stopped at the RGB24 conversion commit.

files: []
source_ref: "video_processor_v4l2.c:27-28, .gitlab-ci.yml:19"