lavc/h2645_parse: Don't automatically remove nuh_layer_id > 0 packets

HEVC standard supports multi-layer streams (ITU-T H.265 02/2018 Annex
F). Each NAL unit belongs to a particular layer defined by nuh_layer_id
in the header.

Currently, all NAL units that do not belong to a base layer are
automatically removed in ff_h2645_packet_split(). Some data may
therefore be lost when future filters/decoders are designed to support
multi-layer streams.

A better approach is to forward nuh_layer_id > 0 packets and let blocks
down the chain decide how to process them. The condition to remove
packets has been moved to hevcdec and cbs.

Found-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Andriy Gelman <andriy.gelman@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/cbs_h2645.c

@@ -565,6 +565,9 @@ static int cbs_h2645_fragment_add_nals(CodedBitstreamContext *ctx,
         AVBufferRef *ref;
         size_t size = nal->size;
 
+        if (nal->nuh_layer_id > 0)
+            continue;
+
         // Remove trailing zeroes.
         while (size > 0 && nal->data[size - 1] == 0)
             --size;

libavcodec/h2645_parse.c

@@ -292,23 +292,22 @@ static int get_bit_length(H2645NAL *nal, int skip_trailing_zeros)
 static int hevc_parse_nal_header(H2645NAL *nal, void *logctx)
 {
     GetBitContext *gb = &nal->gb;
-    int nuh_layer_id;
 
     if (get_bits1(gb) != 0)
         return AVERROR_INVALIDDATA;
 
     nal->type = get_bits(gb, 6);
 
-    nuh_layer_id   = get_bits(gb, 6);
+    nal->nuh_layer_id = get_bits(gb, 6);
     nal->temporal_id = get_bits(gb, 3) - 1;
     if (nal->temporal_id < 0)
         return AVERROR_INVALIDDATA;
 
     av_log(logctx, AV_LOG_DEBUG,
            "nal_unit_type: %d(%s), nuh_layer_id: %d, temporal_id: %d\n",
-           nal->type, hevc_nal_unit_name(nal->type), nuh_layer_id, nal->temporal_id);
+           nal->type, hevc_nal_unit_name(nal->type), nal->nuh_layer_id, nal->temporal_id);
 
-    return nuh_layer_id == 0;
+    return 1;
 }
 
 static int h264_parse_nal_header(H2645NAL *nal, void *logctx)

libavcodec/h2645_parse.h

@@ -56,6 +56,11 @@ typedef struct H2645NAL {
      */
     int temporal_id;
 
+    /*
+     * HEVC only, identifier of layer to which nal unit belongs
+     */
+    int nuh_layer_id;
+
     int skipped_bytes;
     int skipped_bytes_pos_size;
     int *skipped_bytes_pos;

libavcodec/hevc_parse.c

@@ -37,6 +37,8 @@ static int hevc_decode_nal_units(const uint8_t *buf, int buf_size, HEVCParamSets
 
     for (i = 0; i < pkt.nb_nals; i++) {
         H2645NAL *nal = &pkt.nals[i];
+        if (nal->nuh_layer_id > 0)
+            continue;
 
         /* ignore everything except parameter sets and VCL NALUs */
         switch (nal->type) {

libavcodec/hevc_parser.c

@@ -202,6 +202,9 @@ static int parse_nal_units(AVCodecParserContext *s, const uint8_t *buf,
         H2645NAL *nal = &ctx->pkt.nals[i];
         GetBitContext *gb = &nal->gb;
 
+        if (nal->nuh_layer_id > 0)
+            continue;
+
         switch (nal->type) {
         case HEVC_NAL_VPS:
             ff_hevc_decode_nal_vps(gb, avctx, ps);

libavcodec/hevcdec.c

@@ -3077,7 +3077,7 @@ static int decode_nal_units(HEVCContext *s, const uint8_t *buf, int length)
 
         if (s->avctx->skip_frame >= AVDISCARD_ALL ||
             (s->avctx->skip_frame >= AVDISCARD_NONREF
-            && ff_hevc_nal_is_nonref(nal->type)))
+            && ff_hevc_nal_is_nonref(nal->type)) || nal->nuh_layer_id > 0)
             continue;
 
         ret = decode_nal_unit(s, nal);