[FFmpeg-devel] Fwd: framebuffer device demuxer

Måns Rullgård mans
Fri Jan 28 02:10:46 CET 2011


Sorry to chip in so late, but here are some comments on this, mostly
minor.

Stefano Sabatini <stefano.sabatini-lala at poste.it> writes:

> From 9059a39f16131efc768d59784bd0179a2dfce69d Mon Sep 17 00:00:00 2001
> From: Stefano Sabatini <stefano.sabatini-lala at poste.it>
> Date: Tue, 25 Jan 2011 19:40:29 +0100
> Subject: [PATCH] Add Linux framebuffer device.
>
> Based on a patch by Giliard B. de Freitas /com/gmail/giliarde.
>
> See thread:
> Subject: [FFmpeg-devel] Fwd: framebuffer device demuxer
> Date: Sat, 23 May 2009 09:32:13 -0300
> ---
>  Changelog                 |    1 +
>  configure                 |    2 +
>  doc/indevs.texi           |   18 ++++
>  libavdevice/Makefile      |    1 +
>  libavdevice/alldevices.c  |    1 +
>  libavdevice/framebuffer.c |  216 +++++++++++++++++++++++++++++++++++++++++++++
>  6 files changed, 239 insertions(+), 0 deletions(-)
>  create mode 100644 libavdevice/framebuffer.c
>
> diff --git a/Changelog b/Changelog
> index 8b7efb6..1c9166e 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -74,6 +74,7 @@ version <next>:
>  - Lagarith decoder
>  - ffmpeg -copytb option added
>  - IVF muxer added
> +- Linux framebuffer input device added
>  
>  
>  version 0.6:
> diff --git a/configure b/configure
> index 001f00a..e75ad41 100755
> --- a/configure
> +++ b/configure
> @@ -1387,6 +1387,7 @@ alsa_indev_deps="alsa_asoundlib_h snd_pcm_htimestamp"
>  alsa_outdev_deps="alsa_asoundlib_h"
>  bktr_indev_deps_any="dev_bktr_ioctl_bt848_h machine_ioctl_bt848_h dev_video_bktr_ioctl_bt848_h dev_ic_bt8xx_h"
>  dv1394_indev_deps="dv1394 dv_demuxer"
> +framebuffer_indev_deps="linux_fb_h"
>  jack_indev_deps="jack_jack_h"
>  libdc1394_indev_deps="libdc1394"
>  oss_indev_deps_any="soundcard_h sys_soundcard_h"
> @@ -2848,6 +2849,7 @@ if enabled network; then
>      fi
>  fi
>  
> +check_header linux/fb.h
>  check_header linux/videodev.h
>  check_header linux/videodev2.h
>  check_header sys/videoio.h
> diff --git a/doc/indevs.texi b/doc/indevs.texi
> index 8e862ff..e9b1bea 100644
> --- a/doc/indevs.texi
> +++ b/doc/indevs.texi
> @@ -59,6 +59,24 @@ BSD video input device.
>  
>  Linux DV 1394 input device.
>  
> + at section framebuffer
> +
> +Linux framebuffer input device.
> +
> +The name of the framebuffer device to read is a file device node,
> +usually @file{/dev/fb0}.
> +
> +For example, to record from the framebuffer device /dev/fb0 with
> + at file{ffmpeg}:
> + at example
> +ffmpeg -f framebuffer -r 10 -i /dev/fb0 out.avi
> + at end example
> +
> +You can take a single screenshot image with the command:
> + at example
> +ffmpeg -f framebuffer -vframes 1 -r 1 -i /dev/fb0 screenshot.jpeg
> + at end example
> +
>  @section jack
>  
>  JACK input device.

I think "framebuffer" is a bit too generic a name.  After all,
anything with a display of any kind has a framebuffer.  The Linux
framebuffer device generally goes by the name "fbdev", so perhaps that
would be a better name.

> diff --git a/libavdevice/Makefile b/libavdevice/Makefile
> index 1c0630b..f5afeb2 100644
> --- a/libavdevice/Makefile
> +++ b/libavdevice/Makefile
> @@ -14,6 +14,7 @@ OBJS-$(CONFIG_ALSA_OUTDEV)               += alsa-audio-common.o \
>                                              alsa-audio-enc.o
>  OBJS-$(CONFIG_BKTR_INDEV)                += bktr.o
>  OBJS-$(CONFIG_DV1394_INDEV)              += dv1394.o
> +OBJS-$(CONFIG_FRAMEBUFFER_INDEV)         += framebuffer.o
>  OBJS-$(CONFIG_JACK_INDEV)                += jack_audio.o
>  OBJS-$(CONFIG_OSS_INDEV)                 += oss_audio.o
>  OBJS-$(CONFIG_OSS_OUTDEV)                += oss_audio.o
> diff --git a/libavdevice/alldevices.c b/libavdevice/alldevices.c
> index de3bc82..4e79467 100644
> --- a/libavdevice/alldevices.c
> +++ b/libavdevice/alldevices.c
> @@ -42,6 +42,7 @@ void avdevice_register_all(void)
>      REGISTER_INOUTDEV (ALSA, alsa);
>      REGISTER_INDEV    (BKTR, bktr);
>      REGISTER_INDEV    (DV1394, dv1394);
> +    REGISTER_INDEV    (FRAMEBUFFER, framebuffer);
>      REGISTER_INDEV    (JACK, jack);
>      REGISTER_INOUTDEV (OSS, oss);
>      REGISTER_INDEV    (V4L2, v4l2);
> diff --git a/libavdevice/framebuffer.c b/libavdevice/framebuffer.c
> new file mode 100644
> index 0000000..65ebe5c
> --- /dev/null
> +++ b/libavdevice/framebuffer.c
> @@ -0,0 +1,216 @@
> +/*
> + * Copyright (c) 2010 Stefano Sabatini
> + * Copyright (c) 2009 Giliard B. de Freitas <giliarde at gmail.com>
> + * Copyright (C) 2002 Gunnar Monell <gmo at linux.nu>
> + *
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +/**
> + * @file
> + * Linux framebuffer input device,
> + * inspired by code from fbgrab.c by Gunnar Monell.
> + */
> +
> +#include <unistd.h>
> +#include <fcntl.h>
> +#include <sys/ioctl.h>
> +#include <sys/time.h>
> +#include <sys/mman.h>
> +#include <time.h>
> +#include <linux/fb.h>
> +
> +#include "libavutil/mem.h"
> +#include "libavutil/pixdesc.h"
> +#include "libavformat/avformat.h"
> +
> +typedef struct {
> +    int frame_size;          ///< size in bytes of a grabbed frame
> +    AVRational time_base;    ///< time base
> +    int64_t time_frame;      ///< current time
> +
> +    int frame_linesize;      ///< linesize of the output frame
> +    int linesize;            ///< linesize of the read framebuffer
> +    int height;              ///< height of the grab frame
> +    int width;               ///< width of the grab frame
> +    int fd;                  ///< framebuffer device file descriptor
> +
> +    uint8_t *data;           ///< image data
> +} FrameBufferContext;
> +
> +/**
> + * Initialize the framebuffer input device.
> + */
> +av_cold static int framebuffer_read_header(AVFormatContext *avctx, AVFormatParameters *ap)
> +{
> +    FrameBufferContext *fb = avctx->priv_data;
> +    struct fb_var_screeninfo fb_varinfo;
> +    struct fb_fix_screeninfo fb_fixinfo;
> +    AVStream *st = NULL;
> +    enum PixelFormat pix_fmt;
> +    int ret, bits_per_pixel, flags = O_RDONLY;
> +
> +    if (!(st = av_new_stream(avctx, 0)))
> +        return AVERROR(ENOMEM);
> +
> +    if (avctx->flags & AVFMT_FLAG_NONBLOCK)
> +        flags |= O_NONBLOCK;
> +
> +    if ((fb->fd = open(avctx->filename, flags)) == -1) {
> +        ret = AVERROR(errno);
> +        av_log(avctx, AV_LOG_ERROR, "Could not open framebuffer device '%s'.\n", avctx->filename);
> +        goto fail;

You could return directly here and drop the check before close().

> +    }
> +
> +    if (ioctl(fb->fd, FBIOGET_VSCREENINFO, &fb_varinfo) < 0) {
> +        ret = AVERROR(errno);
> +        av_log(avctx, AV_LOG_ERROR, "FBIOGET_VSCREENINFO: %s\n", strerror(errno));
> +        goto fail;
> +    }
> +
> +    if (ioctl(fb->fd, FBIOGET_FSCREENINFO, &fb_fixinfo) < 0) {
> +        ret = AVERROR(errno);
> +        av_log(avctx, AV_LOG_ERROR, "FBIOGET_FSCREENINFO: %s\n", strerror(errno));
> +        goto fail;
> +    }
> +
> +    if (ap->time_base.den <= 0) {
> +        ret = AVERROR(EINVAL);
> +        av_log(avctx, AV_LOG_ERROR, "Invalid time base %d/%d\n", ap->time_base.num, ap->time_base.den);
> +        goto fail;
> +    }
> +
> +    av_set_pts_info(st, 64, 1, 1000000); /* 64 bits pts in microseconds */
> +
> +    fb->width  = fb_varinfo.xres;
> +    fb->height = fb_varinfo.yres;
> +    bits_per_pixel = fb_varinfo.bits_per_pixel;
> +
> +    switch (bits_per_pixel) {
> +    case  8: pix_fmt = PIX_FMT_PAL8  ; break;
> +    case 15: pix_fmt = PIX_FMT_BGR555; break;
> +    case 16: pix_fmt = PIX_FMT_RGB565; break;
> +    case 24: pix_fmt = PIX_FMT_RGB24 ; break;
> +    case 32: pix_fmt = PIX_FMT_RGB32 ; break;
> +    default:
> +        ret = AVERROR(EINVAL);
> +        av_log(avctx, AV_LOG_ERROR, "Image with bits per pixel depth %d not supported.\n",
> +               bits_per_pixel);
> +        goto fail;
> +    }

These are not the only formats possible.  You cannot use bits per
pixel exclusively to determine the format.

> +    fb->frame_linesize = fb_varinfo.xres * ((bits_per_pixel + 7) >> 3);
> +    fb->frame_size     = fb->frame_linesize * fb_varinfo.yres;
> +    fb->linesize       = fb_fixinfo.line_length;
> +    fb->time_base      = ap->time_base;
> +    fb->time_frame     = av_gettime() / av_q2d(ap->time_base);
> +    fb->data = mmap(NULL, fb_fixinfo.line_length * fb_varinfo.yres,
> +                    PROT_READ, MAP_SHARED, fb->fd, 0);
> +    if (fb->data == MAP_FAILED) {
> +        ret = AVERROR(errno);
> +        av_log(avctx, AV_LOG_ERROR, "Error in mmap(): %s\n", strerror(errno));
> +        goto fail;
> +    }
> +
> +    st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
> +    st->codec->codec_id   = CODEC_ID_RAWVIDEO;
> +    st->codec->width      = fb->width;
> +    st->codec->height     = fb->height;
> +    st->codec->pix_fmt    = pix_fmt;
> +    st->codec->time_base  = ap->time_base;
> +    st->codec->bit_rate   = fb->frame_size / av_q2d(ap->time_base) * 8;
> +
> +    av_log(avctx, AV_LOG_INFO, "w:%d h:%d bpp:%d pixfmt:%s tb:%d/%d bit_rate:%d\n",
> +           fb->width, fb->height, bits_per_pixel,
> +           av_pix_fmt_descriptors[pix_fmt].name, ap->time_base.num, ap->time_base.den,
> +           st->codec->bit_rate);
> +    return 0;
> +
> +fail:
> +    if (fb->fd >= 0)
> +        close(fb->fd);
> +    return ret;
> +}
> +
> +/**
> + * Grab a frame from the frame buffer device.
> + *
> + * @param pkt packet holding the grabbed frame
> + * @return frame size in bytes
> + */
> +static int framebuffer_read_packet(AVFormatContext *avctx, AVPacket *pkt)
> +{
> +    FrameBufferContext *fb = avctx->priv_data;
> +    int64_t curtime, delay;
> +    struct timespec ts;
> +    int i, ret;
> +    uint8_t *pin, *pout;
> +
> +    /* wait based on the frame rate */
> +    while (1) {
> +        curtime = av_gettime();
> +        delay = curtime - fb->time_frame * av_q2d(fb->time_base);
> +        if (delay >= 0) {
> +            fb->time_frame += INT64_C(1000000) * av_q2d(fb->time_base);
> +            break;
> +        }
> +        if (avctx->flags & AVFMT_FLAG_NONBLOCK)
> +            return AVERROR(EAGAIN);
> +        ts.tv_sec  =  delay / 1000000;
> +        ts.tv_nsec = (delay % 1000000) * 1000;
> +        nanosleep(&ts, NULL);
> +    }

Using e.g. sem_timedwait(), which takes an absolute timeout, might
give better accuracy here, at least on the off-chance that the process
is descheduled between the av_gettime() and nanosleep() calls.

> +    if ((ret = av_new_packet(pkt, fb->frame_size)) < 0)
> +        return ret;
> +
> +    pkt->pts = curtime;
> +    pin  = fb->data;
> +    pout = pkt->data;
> +    for (i = 0; i < fb->height; i++) {
> +        memcpy(pout, pin, fb->frame_linesize);
> +        pin  += fb->linesize;
> +        pout += fb->frame_linesize;
> +    }
> +
> +    return fb->frame_size;
> +}
> +
> +/**
> + * Close framebuffer input device.
> + *
> + * @return a negative value in case of errors, 0 otherwise

This comment is a lie.  The function always returns 0.  Not that much
could go wrong...

> + */
> +av_cold static int framebuffer_read_close(AVFormatContext *avctx)
> +{
> +    FrameBufferContext *fb = avctx->priv_data;
> +
> +    munmap(fb->data, fb->frame_size);
> +    close(fb->fd);
> +
> +    return 0;
> +}
> +
> +AVInputFormat framebuffer_demuxer = {
> +    .name           = "framebuffer",
> +    .long_name      = NULL_IF_CONFIG_SMALL("Linux framebuffer"),
> +    .priv_data_size = sizeof(FrameBufferContext),
> +    .read_header    = framebuffer_read_header,
> +    .read_packet    = framebuffer_read_packet,
> +    .read_close     = framebuffer_read_close,
> +    .flags          = AVFMT_NOFILE,
> +};

Is AVFMT_NOFILE really correct here?  I'm not sure what its semantics
are supposed to be.

-- 
M?ns Rullg?rd
mans at mansr.com



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