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Code Issues Releases Activity

libavformat: fix rtpdec_av1 regarding OBU size

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Fix the AV1 RTP depacketizer for instances where the OBU elements
did not have their OBU size fields removed according to the
recommendation (SHOULD) of the AV1 RTP specification.

Roger Hardiman courteously reported that the depacketizer doesn't
work correctly for fragmented OBU elements with their OBU size
fields still present and will incorrectly state that the
continuation of such a fragment was unexpected, because the
frag_obu_size field was used as a state and only incremented
when the size field needed to be updated on OBU size field
restoration. This patch solves the slip.

Change-Id: I95af8cc89862e8ecf79aabcf029dd95a20dfd7ad
This commit is contained in:
Chris Hodges
2025-10-21 11:41:06 +02:00
committed by michaelni
parent e10473f13e
commit d12791ef7f
1 changed files with 24 additions and 25 deletions
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49
libavformat/rtpdec_av1.c
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@@ -329,6 +329,8 @@ static int av1_handle_packet(AVFormatContext *ctx, PayloadContext *data,
num_lebs = write_leb(pkt->data + pktpos, obu_payload_size);
data->frag_lebs_res = num_lebs;
pktpos += num_lebs;
} else if (!is_frag_cont) {
data->frag_lebs_res = 0;
}
// copy verbatim or without above header size patch
memcpy(pkt->data + pktpos, buf_ptr, obu_payload_size);
@@ -339,35 +341,32 @@ static int av1_handle_packet(AVFormatContext *ctx, PayloadContext *data,
// if we were handling a fragmented packet and this was the last
// fragment, correct OBU size field
if (data->frag_obu_size && (rem_pkt_size || !is_last_fragmented)) {
uint32_t final_obu_size = data->frag_obu_size + obu_size - data->frag_header_size;
uint8_t *lebptr = pkt->data + data->frag_pkt_leb_pos;
num_lebs = calc_leb_size(final_obu_size);
if (data->frag_lebs_res) {
uint32_t final_obu_size = data->frag_obu_size + obu_size - data->frag_header_size;
uint8_t *lebptr = pkt->data + data->frag_pkt_leb_pos;
num_lebs = calc_leb_size(final_obu_size);
// check if we had allocated enough LEB bytes in header,
// otherwise make some extra space
if (num_lebs > data->frag_lebs_res) {
int extra_bytes = num_lebs - data->frag_lebs_res;
if ((result = av_grow_packet(pkt, extra_bytes)) < 0)
return result;
// update pointer in case buffer address changed
lebptr = pkt->data + data->frag_pkt_leb_pos;
// move existing data for OBU back a bit
memmove(lebptr + extra_bytes, lebptr,
pkt->size - extra_bytes - data->frag_pkt_leb_pos);
// move pktpos further down for following OBUs in same packet.
pktpos += extra_bytes;
// check if we had allocated enough LEB bytes in header,
// otherwise make some extra space
if (num_lebs > data->frag_lebs_res) {
int extra_bytes = num_lebs - data->frag_lebs_res;
if ((result = av_grow_packet(pkt, extra_bytes)) < 0)
return result;
// update pointer in case buffer address changed
lebptr = pkt->data + data->frag_pkt_leb_pos;
// move existing data for OBU back a bit
memmove(lebptr + extra_bytes, lebptr,
pkt->size - extra_bytes - data->frag_pkt_leb_pos);
// move pktpos further down for following OBUs in same packet.
pktpos += extra_bytes;
}
// update OBU size field
write_leb(lebptr, final_obu_size);
}
// update OBU size field
write_leb(lebptr, final_obu_size);
data->frag_obu_size = 0; // signal end of fragment
} else if (is_last_fragmented && !rem_pkt_size) {
// add to total OBU size, so we can fix that in OBU header
// (but only if the OBU size was missing!)
if (needs_size_field || data->frag_obu_size) {
data->frag_obu_size += obu_size;
}
data->frag_obu_size += obu_size;
// fragment not yet finished!
result = -1;
}