v4l2slh264dec: Request large enough bitstream buffer

The Cedrus driver would otherwise choose 1KB buffer, which is too small.
This follows what some drivers do, which is simply to use the size a
packed raw image would have. Specifications do not really guaranty any minimum
compression ratio.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1268>

sys/v4l2codecs/gstv4l2codech264dec.c

@@ -190,6 +190,37 @@ gst_v4l2_codec_h264_dec_stop (GstVideoDecoder * decoder)
   return GST_VIDEO_DECODER_CLASS (parent_class)->stop (decoder);
 }
 
+static gint
+get_pixel_bitdepth (GstV4l2CodecH264Dec * self)
+{
+  gint depth;
+
+  switch (self->chroma_format_idc) {
+    case 0:
+      /* 4:0:0 */
+      depth = self->bitdepth;
+      break;
+    case 1:
+      /* 4:2:0 */
+      depth = self->bitdepth + self->bitdepth / 2;
+      break;
+    case 2:
+      /* 4:2:2 */
+      depth = 2 * self->bitdepth;
+      break;
+    case 3:
+      /* 4:4:4 */
+      depth = 3 * self->bitdepth;
+    default:
+      GST_WARNING_OBJECT (self, "Unsupported chroma format %i",
+          self->chroma_format_idc);
+      depth = 0;
+      break;
+  }
+
+  return depth;
+}
+
 static gboolean
 gst_v4l2_codec_h264_dec_negotiate (GstVideoDecoder * decoder)
 {
@@ -219,7 +250,7 @@ gst_v4l2_codec_h264_dec_negotiate (GstVideoDecoder * decoder)
   gst_v4l2_decoder_streamoff (self->decoder, GST_PAD_SRC);
 
   if (!gst_v4l2_decoder_set_sink_fmt (self->decoder, V4L2_PIX_FMT_H264_SLICE,
-          self->coded_width, self->coded_height)) {
+          self->coded_width, self->coded_height, get_pixel_bitdepth (self))) {
     GST_ELEMENT_ERROR (self, CORE, NEGOTIATION,
         ("Failed to configure H264 decoder"),
         ("gst_v4l2_decoder_set_sink_fmt() failed: %s", g_strerror (errno)));

sys/v4l2codecs/gstv4l2codecvp8dec.c

@@ -159,7 +159,7 @@ gst_v4l2_codec_vp8_dec_negotiate (GstVideoDecoder * decoder)
   gst_v4l2_decoder_streamoff (self->decoder, GST_PAD_SRC);
 
   if (!gst_v4l2_decoder_set_sink_fmt (self->decoder, V4L2_PIX_FMT_VP8_FRAME,
-          self->width, self->height)) {
+          self->width, self->height, 12 /* 8 bits 4:2:0 */ )) {
     GST_ELEMENT_ERROR (self, CORE, NEGOTIATION,
         ("Failed to configure VP8 decoder"),
         ("gst_v4l2_decoder_set_sink_fmt() failed: %s", g_strerror (errno)));

sys/v4l2codecs/gstv4l2decoder.c

@@ -270,7 +270,7 @@ gst_v4l2_decoder_enum_sink_fmt (GstV4l2Decoder * self, gint i,
 
 gboolean
 gst_v4l2_decoder_set_sink_fmt (GstV4l2Decoder * self, guint32 pix_fmt,
-    gint width, gint height)
+    gint width, gint height, gint pixel_bitdepth)
 {
   struct v4l2_format format = (struct v4l2_format) {
     .type = self->sink_buf_type,
@@ -282,6 +282,13 @@ gst_v4l2_decoder_set_sink_fmt (GstV4l2Decoder * self, guint32 pix_fmt,
         },
   };
   gint ret;
+  /* Using raw image size for now, it is guarantied to be large enough */
+  gsize sizeimage = (width * height * pixel_bitdepth) / 8;
+
+  if (self->mplane)
+    format.fmt.pix_mp.plane_fmt[0].sizeimage = sizeimage;
+  else
+    format.fmt.pix.sizeimage = sizeimage;
 
   ret = ioctl (self->video_fd, VIDIOC_S_FMT, &format);
   if (ret < 0) {

sys/v4l2codecs/gstv4l2decoder.h

@@ -51,7 +51,8 @@ gboolean          gst_v4l2_decoder_enum_sink_fmt (GstV4l2Decoder * self,
                                                   gint i, guint32 * out_fmt);
 
 gboolean          gst_v4l2_decoder_set_sink_fmt (GstV4l2Decoder * self, guint32 fmt,
-                                                 gint width, gint height);
+                                                 gint width, gint height,
+                                                 gint pixel_bitdepth);
 
 GstCaps *         gst_v4l2_decoder_enum_src_formats (GstV4l2Decoder * self);