[FFmpeg-devel] [PATCH] v4l2: read the correct time per frame from devices that support a standard
Stefano Sabatini
stefasab at gmail.com
Thu Jan 31 15:37:14 CET 2013
On date Wednesday 2013-01-30 15:11:14 +0100, Giorgio Vazzana encoded:
> 2013/1/30 Stefano Sabatini <stefasab at gmail.com>:
> > On date Monday 2013-01-28 18:09:30 +0100, Giorgio Vazzana encoded:
> >> 2013/1/25 Stefano Sabatini <stefasab at gmail.com>:
> > [...]
> >> >> + if (standard.id == std_id) {
> >> >> + av_log(s1, AV_LOG_DEBUG,
> >> >> + "Current standard: %s, id: %"PRIu64", frameperiod: %d/%d\n",
> >> >> + standard.name, standard.id, tpf->numerator, tpf->denominator);
> >> >> break;
> >> >> + }
> >> >
> >> >> + standard.index++;
> >> >
> >> > seems redundant
> >>
> >> Hmm, if the user does not request a standard on the command line, then
> >> we need to get the current standard, and enumerate the supported
> >> standards one by one until one matches. When we find a match, we can
> >> retrieve the time per frame. So, it should not be redundant.
> >
> > My command was about the line "standard.index++;".
> > Since you set standard.index = i there's little point into assigning
> > it at the end of the loop.
>
> Oh sorry, of course, I misread. Fixed.
>
> > [...]
> >> New patch attached.
> >
> >> From 6e582c0699e6ced4715aaa19726c276940db48ea Mon Sep 17 00:00:00 2001
> >> From: Giorgio Vazzana <mywing81 at gmail.com>
> >> Date: Mon, 28 Jan 2013 17:57:52 +0100
> >> Subject: [PATCH] lavd/v4l2: read the correct time per frame from devices that support a standard
> >>
> >> Generally speaking, there are two types of v4l2 devices [1]:
> >>
> >> 1) devices that support a standard, like PAL or NTFS (tv cards, for example). For
> >> this class of devices the framerate is fixed by the standard (for example PAL uses
> >> 25 fps) and the v4l2 driver cannot usually negotiate a different framerate (unless
> >> it can skip frames on the driver side, to save I/O bandwidth).
> >>
> >> 2) devices for which the notion of standard does not make sense (webcams, for example).
> >> For these devices it is usually possibile to request a desidered framerate.
> >>
> >> In either case, the desidered frame rate can be requested when the VIDIOC_G_PARM
> >> ioctl returns the V4L2_CAP_TIMEPERFRAME flag in the capability field.
> >>
> >> Currently the code does not check for V4L2_CAP_TIMEPERFRAME and supports only the
> >> second category of devices, returning a time per frame of 0/0 for devices in the
> >> first group that do not permit to negotiate the framerate.
> >>
> >> This patch add support to read the correct framerate in all cases.
> >
> > BTW tell if this is fixing a known ticket.
>
> Not yet, but after this patch is applied I think I know what causes bug #1570.
>
> >>
> >> [1] http://linuxtv.org/downloads/v4l-dvb-apis/standard.html
> >> ---
> >> libavdevice/v4l2.c | 119 ++++++++++++++++++++++++++++++++--------------------
> >> 1 files changed, 74 insertions(+), 45 deletions(-)
> >>
> >> diff --git a/libavdevice/v4l2.c b/libavdevice/v4l2.c
> >> index 5f01027..879201f 100644
> >> --- a/libavdevice/v4l2.c
> >> +++ b/libavdevice/v4l2.c
> >> @@ -658,12 +658,10 @@ static int v4l2_set_parameters(AVFormatContext *s1)
> >> struct video_data *s = s1->priv_data;
> >> struct v4l2_standard standard = { 0 };
> >> struct v4l2_streamparm streamparm = { 0 };
> >> - struct v4l2_fract *tpf = &streamparm.parm.capture.timeperframe;
> >> + struct v4l2_fract *tpf;
> >> AVRational framerate_q = { 0 };
> >> int i, ret;
> >>
> >> - streamparm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
> >> -
> >> if (s->framerate &&
> >> (ret = av_parse_video_rate(&framerate_q, s->framerate)) < 0) {
> >> av_log(s1, AV_LOG_ERROR, "Could not parse framerate '%s'.\n",
> >> @@ -672,57 +670,88 @@ static int v4l2_set_parameters(AVFormatContext *s1)
> >> }
> >>
> >> if (s->standard) {
> >> - av_log(s1, AV_LOG_DEBUG, "The V4L2 driver set standard: %s\n",
> >> - s->standard);
> >> - /* set tv standard */
> >> - for(i=0;;i++) {
> >> + if (s->std_id) {
> >> + av_log(s1, AV_LOG_DEBUG, "Setting standard: %s\n", s->standard);
> >> + /* set tv standard */
> >> + for(i = 0; ; i++) {
> >
> > nit++: for_(
>
> Fixed.
>
> >> + standard.index = i;
> >> + ret = v4l2_ioctl(s->fd, VIDIOC_ENUMSTD, &standard);
> >> + if (ret < 0 || !av_strcasecmp(standard.name, s->standard))
> >> + break;
> >> + }
> >
> > Isn't the standard associated to an input fixed? Does it still make
> > sense to enumerate all the standards when you already get a std_id (or
> > can that be changed)?
>
> No, it's not fixed: when you call VIDIOC_ENUMINPUT you get input.std
> which is a set of all supported standards (the supported standards are
> OR-ed together). This means that a Composite input can support, for
> example, both PAL and NTSC, and you can select any of the supported
> standards for that input. Moreover, in ffmpeg the user specifies the
> desired standard by name, so enumerating all the standards until you
> find one that matches is necessary.
>
> >> + if (ret < 0) {
> >> + ret = errno;
> >> + av_log(s1, AV_LOG_ERROR, "Unknown standard '%s'\n", s->standard);
> >
> > Nit: unknown or unsupported ...
>
> Changed.
>
> >> + return AVERROR(ret);
> >> + }
> >> +
> >> + if (v4l2_ioctl(s->fd, VIDIOC_S_STD, &standard.id) < 0) {
> >> + ret = errno;
> >> + av_log(s1, AV_LOG_ERROR, "ioctl(VIDIOC_S_STD): %s\n", strerror(errno));
> >> + return AVERROR(ret);
> >> + }
> >> + } else {
> >> + av_log(s1, AV_LOG_WARNING,
> >> + "This device does not support any standard\n");
> >> + }
> >> + }
> >> +
> >
> >> + /* get standard */
> >> + if (v4l2_ioctl(s->fd, VIDIOC_G_STD, &s->std_id) == 0) {
> >> + tpf = &standard.frameperiod;
> >> + for (i = 0; ; i++) {
> >> standard.index = i;
> >> ret = v4l2_ioctl(s->fd, VIDIOC_ENUMSTD, &standard);
> >> - if (ret < 0 || !av_strcasecmp(standard.name, s->standard))
> >> + if (ret < 0) {
> >> + ret = errno;
> >> + av_log(s1, AV_LOG_ERROR, "ioctl(VIDIOC_ENUMSTD): %s\n", strerror(errno));
> >> + return AVERROR(ret);
> >> + }
> >
> > Same here, couldn't you just set standard.index to the set standard
> > id? Why do you need to enumerate the standards again?
>
> Because, the std_id is not an index into the standard enumeration, it
> is again a set of all supported standards OR-ed together (why a set
> and not only one standard you might ask... because some cards can not
> distinguish, for example, between PAL-B and PAL-G and can switch
> automatically between them). So you need to get the standard set
> std_id (which is of type v4l2_std_id) and then find the match in the
> enumeration: at the point you have the time per frame.
> All this, with several examples, is explained at
> http://linuxtv.org/downloads/v4l-dvb-apis/standard.html
>
> >
> >> + if (standard.id == s->std_id) {
> >> + av_log(s1, AV_LOG_DEBUG,
> >> + "Current standard: %s, id: %"PRIu64", frameperiod: %d/%d\n",
> >> + standard.name, standard.id, tpf->numerator, tpf->denominator);
> >> break;
> >> + }
> >> + standard.index++;
> >> }
> >> - if (ret < 0) {
> >> - av_log(s1, AV_LOG_ERROR, "Unknown standard '%s'\n", s->standard);
> >> - return ret;
> >> - }
> >> + } else {
> >> + tpf = &streamparm.parm.capture.timeperframe;
> >> + }
> >>
> >> - av_log(s1, AV_LOG_DEBUG,
> >> - "The V4L2 driver set standard: %s, id: %"PRIu64"\n",
> >> - s->standard, (uint64_t)standard.id);
> >> - if (v4l2_ioctl(s->fd, VIDIOC_S_STD, &standard.id) < 0) {
> >> - av_log(s1, AV_LOG_ERROR,
> >> - "The V4L2 driver ioctl set standard(%s) failed\n",
> >> - s->standard);
> >> - return AVERROR(EIO);
> >> - }
> >> + streamparm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
> >
> >> + if (v4l2_ioctl(s->fd, VIDIOC_G_PARM, &streamparm) < 0) {
> >> + ret = errno;
> >> + av_log(s1, AV_LOG_ERROR, "ioctl(VIDIOC_G_PARM): %s\n", strerror(errno));
> >> + return AVERROR(ret);
> >> }
> >
> > Note (unrelated): this could be replaced by a macro once and for all
>
> Ok, it can be done later.
>
> Allright, new patch attached.
> From ee0d73edac8de80e1fb53f12fd60e6fddec10cef Mon Sep 17 00:00:00 2001
> From: Giorgio Vazzana <mywing81 at gmail.com>
> Date: Wed, 30 Jan 2013 15:08:04 +0100
> Subject: [PATCH] lavd/v4l2: read the correct time per frame from devices that support a standard
>
> Generally speaking, there are two types of v4l2 devices [1]:
>
> 1) devices that support a standard, like PAL or NTFS (tv cards, for example). For
> this class of devices the framerate is fixed by the standard (for example PAL uses
> 25 fps) and the v4l2 driver cannot usually negotiate a different framerate (unless
> it can skip frames on the driver side, to save I/O bandwidth).
>
> 2) devices for which the notion of standard does not make sense (webcams, for example).
> For these devices it is usually possibile to request a desidered framerate.
>
> In either case, the desidered frame rate can be requested when the VIDIOC_G_PARM
> ioctl returns the V4L2_CAP_TIMEPERFRAME flag in the capability field.
>
> Currently the code does not check for V4L2_CAP_TIMEPERFRAME and supports only the
> second category of devices, returning a time per frame of 0/0 for devices in the
> first group that do not permit to negotiate the framerate.
>
> This patch add support to read the correct framerate in all cases.
>
> [1] http://linuxtv.org/downloads/v4l-dvb-apis/standard.html
> ---
> libavdevice/v4l2.c | 118 ++++++++++++++++++++++++++++++++--------------------
> 1 files changed, 73 insertions(+), 45 deletions(-)
Thanks for the explanation and for the patch, applied.
--
FFmpeg = Fabulous and Friendly Mere Patchable Enlightening God
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