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mxfvanc: Handle empty ANC essence

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Not having any *actual* ANC is totally fine and common usage with several MXF
variants.

In order to properly advance the streams, the essence handler returns an empty
GAP buffer which gets converted to a GST_EVENT_GAP.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2345>
This commit is contained in:
Edward Hervey 2021-06-21 13:23:13 +02:00 committed by Edward Hervey
parent d9c486352c
commit 162e7bd28b
2 changed files with 33 additions and 2 deletions
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15
gst/mxf/mxfdemux.c
View file

@ -2017,7 +2017,20 @@ gst_mxf_demux_handle_generic_container_essence_element (GstMXFDemux * demux,
pad->discont = FALSE;
}
ret = gst_pad_push (GST_PAD_CAST (pad), outbuf);
/* Handlers can provide empty GAP buffers to indicate that the parsed
* content was valid but that nothing meaningful needs to be outputted. In
* such cases we send out a GAP event instead */
if (GST_BUFFER_FLAG_IS_SET (outbuf, GST_BUFFER_FLAG_GAP) &&
gst_buffer_get_size (outbuf) == 0) {
GstEvent *gap = gst_event_new_gap (GST_BUFFER_DTS (outbuf),
GST_BUFFER_DURATION (outbuf));
gst_buffer_unref (outbuf);
GST_DEBUG_OBJECT (pad,
"Replacing empty gap buffer with gap event %" GST_PTR_FORMAT, gap);
gst_pad_push_event (GST_PAD_CAST (pad), gap);
} else {
ret = gst_pad_push (GST_PAD_CAST (pad), outbuf);
}
outbuf = NULL;
ret = gst_flow_combiner_update_flow (demux->flowcombiner, ret);
GST_LOG_OBJECT (demux, "combined return %s", gst_flow_get_name (ret));

20
gst/mxf/mxfvanc.c
View file

@ -116,7 +116,7 @@ mxf_vanc_handle_essence_element (const MXFUL * key, GstBuffer * buffer,
return GST_FLOW_ERROR;
}
if (gst_buffer_get_size (buffer) < 18) {
if (gst_buffer_get_size (buffer) < 2) {
GST_ERROR ("Invalid VANC essence element size");
gst_buffer_unref (buffer);
return GST_FLOW_ERROR;
@ -126,6 +126,24 @@ mxf_vanc_handle_essence_element (const MXFUL * key, GstBuffer * buffer,
gst_byte_reader_init (&reader, map.data, map.size);
num_packets = gst_byte_reader_get_uint16_be_unchecked (&reader);
if (num_packets == 0) {
/* SMPTE 436-1:2013 5.5 The Number of VI Lines or ANC Packets Property
*
* One of the properties in the VI Element is the “Number of Lines” which is
* the number of the VI lines contained in this VI Element. This number can
* be zero if the current VI Element does not have any VI lines in the
* payload space. This capability can be used so every Content Package in a
* file can have a VI Element even if the video stream does not have VI
* lines with every frame (or field.)
*
* The same scheme can be used for ANC packets.
*/
*outbuf = gst_buffer_new ();
GST_BUFFER_FLAG_SET (*outbuf, GST_BUFFER_FLAG_GAP);
ret = GST_FLOW_OK;
goto out;
}
for (i = 0; i < num_packets; i++) {
G_GNUC_UNUSED guint16 line_num;
G_GNUC_UNUSED guint8 wrapping_type;