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h265parser: Skip unused SEI bits differently

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3-byte emulation bytes can confuse the current code that skips
bits at the end of an SEI. Use a simpler method that's also
quicker because it skips all remaining bits in one go instead
of 1 bit at a time.
This commit is contained in:
Jan Schmidt 2019-07-31 00:38:44 +10:00 committed by Jan Schmidt
parent 5e7dbdf585
commit 18b54f8d34
1 changed files with 24 additions and 35 deletions
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59
gst-libs/gst/codecparsers/gsth265parser.c
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@ -2426,28 +2426,17 @@ error:
return GST_H265_PARSER_ERROR; return GST_H265_PARSER_ERROR;
} }
static gboolean
nal_reader_has_more_data_in_payload (NalReader * nr,
guint32 payload_start_pos_bit, guint32 payloadSize)
{
if (nal_reader_is_byte_aligned (nr) &&
(nal_reader_get_pos (nr) == (payload_start_pos_bit + 8 * payloadSize)))
return FALSE;
return TRUE;
}
static GstH265ParserResult static GstH265ParserResult
gst_h265_parser_parse_sei_message (GstH265Parser * parser, gst_h265_parser_parse_sei_message (GstH265Parser * parser,
guint8 nal_type, NalReader * nr, GstH265SEIMessage * sei) guint8 nal_type, NalReader * nr, GstH265SEIMessage * sei)
{ {
guint32 payloadSize; guint32 payloadSizeBytes;
guint8 payload_type_byte, payload_size_byte; guint8 payload_type_byte, payload_size_byte;
guint remaining, payload_size; guint32 remaining, payload_size_bits, next;
guint32 payload_start_pos_bit;
GstH265ParserResult res = GST_H265_PARSER_OK; GstH265ParserResult res = GST_H265_PARSER_OK;
GST_DEBUG ("parsing \"Sei message\""); GST_DEBUG ("parsing \"SEI message\" %u bits available",
nal_reader_get_remaining (nr));
memset (sei, 0, sizeof (*sei)); memset (sei, 0, sizeof (*sei));
@ -2455,20 +2444,21 @@ gst_h265_parser_parse_sei_message (GstH265Parser * parser,
READ_UINT8 (nr, payload_type_byte, 8); READ_UINT8 (nr, payload_type_byte, 8);
sei->payloadType += payload_type_byte; sei->payloadType += payload_type_byte;
} while (payload_type_byte == 0xff); } while (payload_type_byte == 0xff);
payloadSize = 0; payloadSizeBytes = 0;
do { do {
READ_UINT8 (nr, payload_size_byte, 8); READ_UINT8 (nr, payload_size_byte, 8);
payloadSize += payload_size_byte; payloadSizeBytes += payload_size_byte;
} }
while (payload_size_byte == 0xff); while (payload_size_byte == 0xff);
remaining = nal_reader_get_remaining (nr); remaining = nal_reader_get_remaining (nr);
payload_size = payloadSize * 8 < remaining ? payloadSize * 8 : remaining; payload_size_bits =
payloadSizeBytes * 8 < remaining ? payloadSizeBytes * 8 : remaining;
next = nal_reader_get_pos (nr) + payload_size_bits;
payload_start_pos_bit = nal_reader_get_pos (nr);
GST_DEBUG GST_DEBUG
("SEI message received: payloadType %u, payloadSize = %u bytes", ("SEI message received: payloadType %u, payloadSize = %u bits",
sei->payloadType, payload_size); sei->payloadType, payload_size_bits);
if (nal_type == GST_H265_NAL_PREFIX_SEI) { if (nal_type == GST_H265_NAL_PREFIX_SEI) {
switch (sei->payloadType) { switch (sei->payloadType) {
@ -2501,7 +2491,7 @@ gst_h265_parser_parse_sei_message (GstH265Parser * parser,
default: default:
/* Just consume payloadSize bytes, which does not account for /* Just consume payloadSize bytes, which does not account for
emulation prevention bytes */ emulation prevention bytes */
if (!nal_reader_skip_long (nr, payload_size)) if (!nal_reader_skip_long (nr, payload_size_bits))
goto error; goto error;
res = GST_H265_PARSER_OK; res = GST_H265_PARSER_OK;
break; break;
@ -2511,7 +2501,7 @@ gst_h265_parser_parse_sei_message (GstH265Parser * parser,
default: default:
/* Just consume payloadSize bytes, which does not account for /* Just consume payloadSize bytes, which does not account for
emulation prevention bytes */ emulation prevention bytes */
if (!nal_reader_skip_long (nr, payload_size)) if (!nal_reader_skip_long (nr, payload_size_bits))
goto error; goto error;
res = GST_H265_PARSER_OK; res = GST_H265_PARSER_OK;
break; break;
@ -2524,19 +2514,18 @@ gst_h265_parser_parse_sei_message (GstH265Parser * parser,
* it is present, the size will be less than total PayloadSize since the * it is present, the size will be less than total PayloadSize since the
* size of reserved_payload_extension is supposed to be * size of reserved_payload_extension is supposed to be
* 8 * payloadSize - nEarlierBits - nPayloadZeroBits -1 which means the * 8 * payloadSize - nEarlierBits - nPayloadZeroBits -1 which means the
* the current implementation will still skip all unnecessary bits correctly. * the current implementation will still skip all unnecessary bits correctly. */
* In theory, we can have a more optimized implementation by skipping the
* data left in PayLoadSize without out individually checking for each bits, /* Always make sure all the advertised SEI bits
* since the totoal size will be always less than payloadSize*/ * were consumed during parsing. This is sufficient to skip to the next
if (nal_reader_has_more_data_in_payload (nr, payload_start_pos_bit, * byte aligned position after the SEI payload because we start
payloadSize)) { * at a byte-aligned position and calculate the 'next' position as a
/* Skip the byte alignment bits */ * multiple of 8 bits, and this correctly skips any three-byte emulation
if (!nal_reader_skip (nr, 1)) * bytes encountered without getting confused. */
if (next > nal_reader_get_pos (nr)) {
GST_LOG ("Skipping %u unused SEI bits", next - nal_reader_get_pos (nr));
if (!nal_reader_skip_long (nr, next - nal_reader_get_pos (nr)))
goto error; goto error;
while (!nal_reader_is_byte_aligned (nr)) {
if (!nal_reader_skip (nr, 1))
goto error;
}
} }
return res; return res;