v4l2: correct frame rate if enumeration fails

The streaming parameters depend on the format, so the format must be
set explicitly, then the streaming parameters queried every time.

This essentially reverts 1bb938e4.

modules/access/v4l2/video.c

@@ -765,13 +765,12 @@ static const struct v4l2_fract infinity = { 1, 0 };
 /**
  * Finds the highest frame rate possible of a certain V4L2 format.
  * @param fmt V4L2 capture format [IN]
- * @param parm V4L2 capture streaming parameters [IN]
  * @param it V4L2 frame interval [OUT]
+ * @return 0 on success, -1 on error.
  */
-static void FindMaxRate (vlc_object_t *obj, int fd,
-                         const struct v4l2_format *restrict fmt,
-                         const struct v4l2_streamparm *restrict parm,
-                         struct v4l2_fract *restrict it)
+static int FindMaxRate (vlc_object_t *obj, int fd,
+                        const struct v4l2_format *restrict fmt,
+                        struct v4l2_fract *restrict it)
 {
     struct v4l2_frmivalenum fie = {
         .pixel_format = fmt->fmt.pix.pixelformat,
@@ -780,19 +779,26 @@ static void FindMaxRate (vlc_object_t *obj, int fd,
     };
     /* Mind that maximum rate means minimum interval */
 
-    if (!(parm->parm.capture.capability & V4L2_CAP_TIMEPERFRAME))
-    {
-        *it = parm->parm.capture.timeperframe;
-        msg_Dbg (obj, "  constant frame interval: %"PRIu32"/%"PRIu32,
-                 it->numerator, it->denominator);
-    }
-    else
     if (v4l2_ioctl (fd, VIDIOC_ENUM_FRAMEINTERVALS, &fie) < 0)
     {
-        msg_Warn (obj, "  unknown frame intervals: %m");
-        *it = parm->parm.capture.timeperframe;
-        msg_Dbg (obj, "  default frame interval: %"PRIu32"/%"PRIu32,
-                 it->numerator, it->denominator);
+        msg_Dbg (obj, "  unknown frame intervals: %m");
+        /* Frame intervals cannot be enumerated. Set the format and then
+         * get the streaming parameters to figure out the default frame
+         * interval. This is not necessarily the maximum though. */
+        struct v4l2_format dummy_fmt = *fmt;
+        struct v4l2_streamparm parm = { .type = V4L2_BUF_TYPE_VIDEO_CAPTURE };
+
+        if (v4l2_ioctl (fd, VIDIOC_S_FMT, &dummy_fmt) < 0
+         || v4l2_ioctl (fd, VIDIOC_G_PARM, &parm) < 0)
+        {
+            *it = infinity;
+            return -1;
+        }
+
+        *it = parm.parm.capture.timeperframe;
+        msg_Dbg (obj, "  %s frame interval: %"PRIu32"/%"PRIu32,
+                 (parm.parm.capture.capability & V4L2_CAP_TIMEPERFRAME)
+                 ? "default" : "constant", it->numerator, it->denominator);
     }
     else
     switch (fie.type)
@@ -803,14 +809,12 @@ static void FindMaxRate (vlc_object_t *obj, int fd,
             {
                 if (fcmp (&fie.discrete, it) < 0)
                     *it = fie.discrete;
-                msg_Dbg (obj, "  discrete frame interval: %"PRIu32"/%"PRIu32,
-                         fie.discrete.numerator, fie.discrete.denominator);
                 fie.index++;
             }
             while (v4l2_ioctl (fd, VIDIOC_ENUM_FRAMEINTERVALS, &fie) >= 0);
 
-            msg_Dbg (obj, "  best discrete frame interval: %"PRIu32"/%"PRIu32,
-                     it->numerator, it->denominator);
+            msg_Dbg (obj, "  %s frame interval: %"PRIu32"/%"PRIu32,
+                     "discrete", it->numerator, it->denominator);
             break;
 
         case V4L2_FRMIVAL_TYPE_STEPWISE:
@@ -826,6 +830,7 @@ static void FindMaxRate (vlc_object_t *obj, int fd,
             *it = fie.stepwise.min;
             break;
     }
+    return 0;
 }
 
 #undef SetupFormat
@@ -850,15 +855,7 @@ int SetupFormat (vlc_object_t *obj, int fd, uint32_t fourcc,
         msg_Err (obj, "cannot get default format: %m");
         return -1;
     }
-    if (v4l2_ioctl (fd, VIDIOC_G_PARM, parm) < 0)
-    {
-        msg_Err (obj, "cannot get streaming parameters: %m");
-        return -1;
-    }
-
     fmt->fmt.pix.pixelformat = fourcc;
-    parm->parm.capture.capturemode = 0; /* normal video mode */
-    parm->parm.capture.extendedmode = 0;
 
     struct v4l2_frmsizeenum fse = {
         .pixel_format = fourcc,
@@ -874,7 +871,7 @@ int SetupFormat (vlc_object_t *obj, int fd, uint32_t fourcc,
         fmt->fmt.pix.height = height;
         msg_Dbg (obj, " requested frame size: %"PRIu32"x%"PRIu32,
                  width, height);
-        FindMaxRate (obj, fd, fmt, parm, &best_it);
+        FindMaxRate (obj, fd, fmt, &best_it);
     }
     else
     if (v4l2_ioctl (fd, VIDIOC_ENUM_FRAMESIZES, &fse) < 0)
@@ -883,7 +880,7 @@ int SetupFormat (vlc_object_t *obj, int fd, uint32_t fourcc,
         msg_Dbg (obj, " unknown frame sizes: %m");
         msg_Dbg (obj, " current frame size: %"PRIu32"x%"PRIu32,
                  fmt->fmt.pix.width, fmt->fmt.pix.height);
-        FindMaxRate (obj, fd, fmt, parm, &best_it);
+        FindMaxRate (obj, fd, fmt, &best_it);
     }
     else
     switch (fse.type)
@@ -895,7 +892,7 @@ int SetupFormat (vlc_object_t *obj, int fd, uint32_t fourcc,
 
                 msg_Dbg (obj, " frame size %"PRIu32"x%"PRIu32,
                          fse.discrete.width, fse.discrete.height);
-                FindMaxRate (obj, fd, fmt, parm, &cur_it);
+                FindMaxRate (obj, fd, fmt, &cur_it);
 
                 int64_t c = fcmp (&cur_it, &best_it);
                 uint64_t area = fse.discrete.width * fse.discrete.height;
@@ -925,12 +922,6 @@ int SetupFormat (vlc_object_t *obj, int fd, uint32_t fourcc,
                 msg_Dbg (obj, "  with %"PRIu32"x%"PRIu32" steps",
                          fse.stepwise.step_width, fse.stepwise.step_height);
 
-            if (!(parm->parm.capture.capability & V4L2_CAP_TIMEPERFRAME))
-            {   /* Frame rate is constant, lets maximize resolution */
-                fmt->fmt.pix.width = fse.stepwise.max_width;
-                fmt->fmt.pix.height = fse.stepwise.max_height;
-            }
-            else
             /* FIXME: slow and dumb */
             for (uint32_t width =  fse.stepwise.min_width;
                           width <= fse.stepwise.max_width;
@@ -941,7 +932,7 @@ int SetupFormat (vlc_object_t *obj, int fd, uint32_t fourcc,
                 {
                     struct v4l2_fract cur_it;
 
-                    FindMaxRate (obj, fd, fmt, parm, &cur_it);
+                    FindMaxRate (obj, fd, fmt, &cur_it);
 
                     int64_t c = fcmp (&cur_it, &best_it);
                     uint64_t area = width * height;
@@ -960,15 +951,26 @@ int SetupFormat (vlc_object_t *obj, int fd, uint32_t fourcc,
             break;
     }
 
-    parm->parm.capture.timeperframe = best_it;
-
+    /* Set the final format */
     if (v4l2_ioctl (fd, VIDIOC_S_FMT, fmt) < 0)
     {
         msg_Err (obj, "cannot set format: %m");
         return -1;
     }
+
+    /* Now that the final format is set, fetch and override parameters */
+    if (v4l2_ioctl (fd, VIDIOC_G_PARM, parm) < 0)
+    {
+        msg_Err (obj, "cannot get streaming parameters: %m");
+        return -1;
+    }
+    parm->parm.capture.capturemode = 0; /* normal video mode */
+    parm->parm.capture.extendedmode = 0;
+    if (best_it.denominator != 0)
+        parm->parm.capture.timeperframe = best_it;
     if (v4l2_ioctl (fd, VIDIOC_S_PARM, parm) < 0)
         msg_Warn (obj, "cannot set streaming parameters: %m");
+
     ResetCrop (obj, fd); /* crop depends on frame size */
 
     return 0;