In video4linux2, in the case the timebase value in ap is 0/0, read the

timebase value already set in the driver, and set it back in the codec
stream, rather than leaving the invalid value of 0/0.

In particular, fix ffmpeg grabbing timestamps when the timebase value
is not set through the CLI.

Originally committed as revision 26224 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/indevs.texi

@@ -146,6 +146,8 @@ devices and the command @file{v4l-info} for Video4Linux2 devices.
 
 If the size for the device is set to 0x0, the input device will
 try to autodetect the size to use.
+Only for the video4linux2 device, if the frame rate is set to 0/0 the
+input device will use the frame rate value already set in the driver.
 
 Video4Linux support is deprecated since Linux 2.6.30, and will be
 dropped in later versions.
@@ -153,13 +155,16 @@ dropped in later versions.
 Follow some usage examples of the video4linux devices with the ff*
 tools.
 @example
-# Grab and show the input of a video4linux device.
+# Grab and show the input of a video4linux device, frame rate is set
+# to the default of 25/1.
 ffplay -s 320x240 -f video4linux /dev/video0
 
 # Grab and show the input of a video4linux2 device, autoadjust size.
 ffplay -f video4linux2 /dev/video0
 
-# Grab and record the input of a video4linux2 device, autoadjust size.
+# Grab and record the input of a video4linux2 device, autoadjust size,
+# frame rate value defaults to 0/0 so it is read from the video4linux2
+# driver.
 ffmpeg -f video4linux2 -i /dev/video0 out.mpeg
 @end example
 

libavdevice/avdevice.h

@@ -23,7 +23,7 @@
 
 #define LIBAVDEVICE_VERSION_MAJOR 52
 #define LIBAVDEVICE_VERSION_MINOR  2
-#define LIBAVDEVICE_VERSION_MICRO  2
+#define LIBAVDEVICE_VERSION_MICRO  3
 
 #define LIBAVDEVICE_VERSION_INT AV_VERSION_INT(LIBAVDEVICE_VERSION_MAJOR, \
                                                LIBAVDEVICE_VERSION_MINOR, \

libavdevice/v4l2.c

@@ -514,6 +514,19 @@ static int v4l2_set_parameters(AVFormatContext *s1, AVFormatParameters *ap)
             ap->time_base.num = tpf->numerator;
             ap->time_base.den = tpf->denominator;
         }
+    } else {
+        /* if timebase value is not set in ap, read the timebase value
+         * from the driver and set it in ap */
+        struct v4l2_streamparm streamparm = { 0 };
+        struct v4l2_fract *tpf = &streamparm.parm.capture.timeperframe;
+
+        streamparm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+        if (ioctl(s->fd, VIDIOC_G_PARM, &streamparm) != 0) {
+            av_log(s1, AV_LOG_ERROR, "ioctl(VIDIOC_G_PARM): %s\n", strerror(errno));
+            return AVERROR(errno);
+        }
+        ap->time_base.num = tpf->numerator;
+        ap->time_base.den = tpf->denominator;
     }
 
     return 0;