decoder: introduce lists of units to decode before/after frame.

Theory of operations: all units marked as "slice" are moved to the "units"
list. Since this list only contains slice data units, the prev_slice pointer
was removed. Besides, we now maintain two extra lists of units to be decoded
before or after slice data units.

In particular, all units in the "pre_units" list will be decoded before
GstVaapiDecoder::start_frame() is called and units in the "post_units"
list will be decoded after GstVaapiDecoder::end_frame() is called.

gst-libs/gst/vaapi/gstvaapidecoder.c

@@ -150,6 +150,7 @@ do_parse(GstVaapiDecoder *decoder,
     GstVaapiDecoderFrame *frame;
     GstVaapiDecoderUnit *unit;
     GstVaapiDecoderStatus status;
+    GSList **unit_list_ptr;
 
     *got_unit_size_ptr = 0;
     *got_frame_ptr = FALSE;
@@ -178,23 +179,48 @@ do_parse(GstVaapiDecoder *decoder,
         return status;
     }
 
-    if (GST_VAAPI_DECODER_UNIT_IS_FRAME_START(unit) && frame->prev_slice) {
+    if (GST_VAAPI_DECODER_UNIT_IS_FRAME_START(unit) && frame->units) {
         parser_state_set_pending_unit(ps, adapter, unit);
         goto got_frame;
     }
 
 got_unit:
     unit->offset = frame->output_offset;
-    frame->units = g_slist_prepend(frame->units, unit);
     frame->output_offset += unit->size;
+
     if (GST_VAAPI_DECODER_UNIT_IS_SLICE(unit))
-        frame->prev_slice = unit;
+        unit_list_ptr = &frame->units;
+    else if (GST_VAAPI_DECODER_UNIT_IS_FRAME_END(unit))
+        unit_list_ptr = &frame->post_units;
+    else
+        unit_list_ptr = &frame->pre_units;
+    *unit_list_ptr = g_slist_prepend(*unit_list_ptr, unit);
 
     *got_unit_size_ptr = unit->size;
     if (GST_VAAPI_DECODER_UNIT_IS_FRAME_END(unit)) {
     got_frame:
-        frame->units = g_slist_reverse(frame->units);
-        *got_frame_ptr = TRUE;
+        frame->units      = g_slist_reverse(frame->units);
+        frame->pre_units  = g_slist_reverse(frame->pre_units);
+        frame->post_units = g_slist_reverse(frame->post_units);
+        *got_frame_ptr    = TRUE;
+    }
+    return GST_VAAPI_DECODER_STATUS_SUCCESS;
+}
+
+static GstVaapiDecoderStatus
+do_decode_list(GstVaapiDecoder *decoder, GSList *units)
+{
+    GstVaapiDecoderClass * const klass = GST_VAAPI_DECODER_GET_CLASS(decoder);
+    GstVaapiDecoderStatus status;
+    GSList *l;
+
+    for (l = units; l != NULL; l = l->next) {
+        GstVaapiDecoderUnit * const unit = l->data;
+        if (GST_VAAPI_DECODER_UNIT_IS_SKIPPED(unit))
+            continue;
+        status = klass->decode(decoder, unit);
+        if (status != GST_VAAPI_DECODER_STATUS_SUCCESS)
+            return status;
     }
     return GST_VAAPI_DECODER_STATUS_SUCCESS;
 }
@@ -206,33 +232,35 @@ do_decode(GstVaapiDecoder *decoder, GstVideoCodecFrame *base_frame)
     GstVaapiParserState * const ps = &decoder->priv->parser_state;
     GstVaapiDecoderFrame * const frame = base_frame->user_data;
     GstVaapiDecoderStatus status;
-    GSList *l;
 
     ps->current_frame = base_frame;
 
-    if (klass->start_frame) {
-        for (l = frame->units; l != NULL; l = l->next) {
-            GstVaapiDecoderUnit * const unit = l->data;
-            if (GST_VAAPI_DECODER_UNIT_IS_SLICE(unit)) {
-                status = klass->start_frame(decoder, unit);
-                if (status != GST_VAAPI_DECODER_STATUS_SUCCESS)
-                    return status;
-                break;
-            }
-        }
-    }
-
-    for (l = frame->units; l != NULL; l = l->next) {
-        GstVaapiDecoderUnit * const unit = l->data;
-        if (GST_VAAPI_DECODER_UNIT_IS_SKIPPED(unit))
-            continue;
-        status = klass->decode(decoder, unit);
+    if (frame->pre_units) {
+        status = do_decode_list(decoder, frame->pre_units);
         if (status != GST_VAAPI_DECODER_STATUS_SUCCESS)
             return status;
     }
 
-    if (klass->end_frame) {
-        status = klass->end_frame(decoder);
+    if (frame->units) {
+        if (klass->start_frame) {
+            status = klass->start_frame(decoder, frame->units->data);
+            if (status != GST_VAAPI_DECODER_STATUS_SUCCESS)
+                return status;
+        }
+
+        status = do_decode_list(decoder, frame->units);
+        if (status != GST_VAAPI_DECODER_STATUS_SUCCESS)
+            return status;
+
+        if (klass->end_frame) {
+            status = klass->end_frame(decoder);
+            if (status != GST_VAAPI_DECODER_STATUS_SUCCESS)
+                return status;
+        }
+    }
+
+    if (frame->post_units) {
+        status = do_decode_list(decoder, frame->post_units);
         if (status != GST_VAAPI_DECODER_STATUS_SUCCESS)
             return status;
     }

gst-libs/gst/vaapi/gstvaapidecoder_frame.c

@@ -37,6 +37,17 @@ gst_vaapi_decoder_frame_class(void)
     return &GstVaapiDecoderFrameClass;
 }
 
+static inline void
+free_units(GSList **units_ptr)
+{
+    GSList * const units = *units_ptr;
+
+    if (units) {
+        g_slist_free_full(units, (GDestroyNotify)gst_vaapi_mini_object_unref);
+        *units_ptr = NULL;
+    }
+}
+
 /**
  * gst_vaapi_decoder_frame_new:
  *
@@ -47,17 +58,8 @@ gst_vaapi_decoder_frame_class(void)
 GstVaapiDecoderFrame *
 gst_vaapi_decoder_frame_new(void)
 {
-    GstVaapiDecoderFrame *frame;
-
-    frame = (GstVaapiDecoderFrame *)
-        gst_vaapi_mini_object_new(gst_vaapi_decoder_frame_class());
-    if (!frame)
-        return NULL;
-
-    frame->output_offset = 0;
-    frame->units = NULL;
-    frame->prev_slice = NULL;
-    return frame;
+    return (GstVaapiDecoderFrame *)
+        gst_vaapi_mini_object_new0(gst_vaapi_decoder_frame_class());
 }
 
 /**
@@ -73,9 +75,7 @@ gst_vaapi_decoder_frame_new(void)
 void
 gst_vaapi_decoder_frame_free(GstVaapiDecoderFrame *frame)
 {
-    if (frame->units) {
-        g_slist_free_full(frame->units,
-            (GDestroyNotify)gst_vaapi_mini_object_unref);
-        frame->units = NULL;
-    }
+    free_units(&frame->units);
+    free_units(&frame->pre_units);
+    free_units(&frame->post_units);
 }

gst-libs/gst/vaapi/gstvaapidecoder_frame.h

@@ -54,7 +54,9 @@ typedef enum {
  * @output_offset: current offset to the reconstructed #GstBuffer for
  *    this #GstVideoCodecFrame. This is used to initialize the decoder
  *    unit offset
- * @units: list of #GstVaapiDecoderUnit objects
+ * @units: list of #GstVaapiDecoderUnit objects (slice data)
+ * @pre_units: list of units to decode before GstVaapiDecoder:start_frame()
+ * @post_units: list of units to decode after GstVaapiDecoder:end_frame()
  * @prev_slice: previous #GstVaapiDecoderUnit that was a slice, or NULL
  *    if no slice data unit was received yet
  *
@@ -68,7 +70,8 @@ struct _GstVaapiDecoderFrame {
 
     guint                output_offset;
     GSList              *units;
-    GstVaapiDecoderUnit *prev_slice;
+    GSList              *pre_units;
+    GSList              *post_units;
 };
 
 G_GNUC_INTERNAL

gst-libs/gst/vaapi/gstvaapidecoder_unit.h

@@ -40,7 +40,7 @@ typedef struct _GstVaapiDecoderUnit             GstVaapiDecoderUnit;
  * @GST_VAAPI_DECODER_UNIT_FLAG_FRAME_START: marks the start of a frame.
  * @GST_VAAPI_DECODER_UNIT_FLAG_FRAME_END: marks the end of a frame.
  * @GST_VAAPI_DECODER_UNIT_FLAG_STREAM_END: marks the end of a stream.
- * @GST_VAAPI_DECODER_UNIT_FLAG_SLICE: marks the unit contains slice data.
+ * @GST_VAAPI_DECODER_UNIT_FLAG_SLICE: the unit contains slice data.
  * @GST_VAAPI_DECODER_UNIT_FLAG_SKIP: marks the unit as unused/skipped.
  *
  * Flags for #GstVaapiDecoderUnit.