[FFmpeg-devel] [PATCH 4/4] avcodec/cbs_h265: add missing support for reserved_payload_extension_data SEI bits

[James Almer]

Fixes ticket #8622

Signed-off-by: James Almer <jamrial at gmail.com>
---
It fixes it assuming the Picture Timing in that sample is not being misparsed
by cbs_h265.
We're compliant with the latest revision of the spec, so any
reserved_payload_extension_data found in a sample created today is almost
guaranteed to be bogus. But the spec states that they should be skipped if
found, for forward compatibility reasons.
Would be worth checking if the nvenc encoder is at fault, writing faulty SEI
messages.

This patch could for that matter make many potential cases of undiscovered
cbs_h265 SEI misparsing be handled as if the remaining bits were these reserved
bits.

 libavcodec/cbs_h265.h                 |  1 +
 libavcodec/cbs_h265_syntax_template.c | 44 +++++++++++++++++++++++++--
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/libavcodec/cbs_h265.h b/libavcodec/cbs_h265.h
index 2c1e153ad9..73897f77a4 100644
--- a/libavcodec/cbs_h265.h
+++ b/libavcodec/cbs_h265.h
@@ -715,6 +715,7 @@ typedef struct H265RawSEIPayload {
             AVBufferRef *data_ref;
         } other;
     } payload;
+    H265RawExtensionData extension_data;
 } H265RawSEIPayload;
 
 typedef struct H265RawSEI {
diff --git a/libavcodec/cbs_h265_syntax_template.c b/libavcodec/cbs_h265_syntax_template.c
index f978e16549..ef3254d27f 100644
--- a/libavcodec/cbs_h265_syntax_template.c
+++ b/libavcodec/cbs_h265_syntax_template.c
@@ -2054,11 +2054,43 @@ static int FUNC(sei_alpha_channel_info)(CodedBitstreamContext *ctx,
     return 0;
 }
 
+static int FUNC(payload_extension)(CodedBitstreamContext *ctx, RWContext *rw,
+                                   H265RawExtensionData *current, uint32_t payload_size,
+                                   int cur_pos)
+{
+    int err, i;
+
+#ifdef READ
+    if (cbs_h265_payload_extension_present(rw, payload_size, cur_pos)) {
+        GetBitContext tmp = *rw;
+        int payload_zero_bits, bits_left = 8 * payload_size - cur_pos;
+        if (bits_left > 8)
+            skip_bits_long(&tmp, bits_left - 8);
+        payload_zero_bits = ff_ctz(get_bits(&tmp, FFMIN(bits_left, 8)));
+        if (payload_zero_bits >= bits_left - 1)
+            return AVERROR_INVALIDDATA;
+        current->bit_length = bits_left - payload_zero_bits - 1;
+        allocate(current->data, (current->bit_length + 7) / 8);
+        for (i = 0; i < current->bit_length; i++) {
+            uint8_t bit;
+            xu(1, reserved_payload_extension_data, bit, 0, 1, 0);
+            current->data[i / 8] |= bit << (7 - i % 8);
+        }
+    }
+#else
+    for (i = 0; i < current->bit_length; i++)
+        xu(1, reserved_payload_extension_data,
+           current->data[i / 8] >> (7 - i % 8) & 1, 0, 1, 0);
+#endif
+
+    return 0;
+}
+
 static int FUNC(sei_payload)(CodedBitstreamContext *ctx, RWContext *rw,
                              H265RawSEIPayload *current, int prefix)
 {
     int err, i;
-    int start_position, end_position;
+    int start_position, current_position, end_position;
 
 #ifdef READ
     start_position = get_bits_count(rw);
@@ -2122,7 +2154,15 @@ static int FUNC(sei_payload)(CodedBitstreamContext *ctx, RWContext *rw,
         }
     }
 
-    if (byte_alignment(rw)) {
+#ifdef READ
+    current_position = get_bits_count(rw) - start_position;
+    if (current_position != 8 * current->payload_size) {
+#else
+    current_position = put_bits_count(rw) - start_position;
+    if (byte_alignment(rw) || current->extension_data.bit_length) {
+#endif
+        CHECK(FUNC(payload_extension)(ctx, rw, &current->extension_data,
+                                      current->payload_size, current_position));
         fixed(1, bit_equal_to_one, 1);
         while (byte_alignment(rw))
             fixed(1, bit_equal_to_zero, 0);
-- 
2.26.0