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mxfdec: Compute essence container offsets and lengths into mxf->partitions

This commit is contained in:
Tomas Härdin 2011-12-08 11:18:21 +01:00
parent 289bc14449
commit 336246238e
1 changed files with 69 additions and 0 deletions
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69
libavformat/mxfdec.c
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@ -79,6 +79,8 @@ typedef struct {
int index_sid;
int body_sid;
int64_t this_partition;
int64_t essence_offset; /* absolute offset of essence */
int64_t essence_length;
} MXFPartition;
typedef struct {
@ -1401,6 +1403,46 @@ static int mxf_parse_handle_partition_or_eof(MXFContext *mxf)
return mxf->parsing_backward ? mxf_seek_to_previous_partition(mxf) : 1;
}
/**
* Figures out the proper offset and length of the essence container in each partition
*/
static void mxf_compute_essence_containers(MXFContext *mxf)
{
int x;
/* everything is already correct */
if (mxf->op == OPAtom)
return;
for (x = 0; x < mxf->partitions_count; x++) {
MXFPartition *p = &mxf->partitions[x];
if (!p->body_sid)
continue; /* BodySID == 0 -> no essence */
if (x >= mxf->partitions_count - 1)
break; /* last partition - can't compute length (and we don't need to) */
/* essence container spans to the next partition */
p->essence_length = mxf->partitions[x+1].this_partition - p->essence_offset;
if (p->essence_length < 0) {
/* next ThisPartition < essence_offset */
p->essence_length = 0;
av_log(mxf->fc, AV_LOG_ERROR, "partition %i: bad ThisPartition = %lx\n",
x+1, mxf->partitions[x+1].this_partition);
}
}
}
static int64_t round_to_kag(int64_t position, int kag_size)
{
/* TODO: account for run-in? the spec isn't clear whether KAG should account for it */
/* NOTE: kag_size may be any integer between 1 - 2^10 */
int64_t ret = (position / kag_size) * kag_size;
return ret == position ? ret : ret + kag_size;
}
static int mxf_read_header(AVFormatContext *s, AVFormatParameters *ap)
{
MXFContext *mxf = s->priv_data;
@ -1432,6 +1474,30 @@ static int mxf_read_header(AVFormatContext *s, AVFormatParameters *ap)
if (IS_KLV_KEY(klv.key, mxf_encrypted_triplet_key) ||
IS_KLV_KEY(klv.key, mxf_essence_element_key) ||
IS_KLV_KEY(klv.key, mxf_system_item_key)) {
if (!mxf->current_partition->essence_offset) {
/* for OP1a we compute essence_offset
* for OPAtom we point essence_offset after the KL (usually op1a_essence_offset + 20 or 25)
* TODO: for OP1a we could eliminate this entire if statement, always stopping parsing at op1a_essence_offset
* for OPAtom we still need the actual essence_offset though (the KL's length can vary)
*/
int64_t op1a_essence_offset =
round_to_kag(mxf->current_partition->this_partition +
mxf->current_partition->pack_length, mxf->current_partition->kag_size) +
round_to_kag(mxf->current_partition->header_byte_count, mxf->current_partition->kag_size) +
round_to_kag(mxf->current_partition->index_byte_count, mxf->current_partition->kag_size);
if (mxf->op == OPAtom) {
/* point essence_offset to the actual data
* OPAtom has all the essence in one big KLV
*/
mxf->current_partition->essence_offset = avio_tell(s->pb);
mxf->current_partition->essence_length = klv.length;
} else {
/* NOTE: op1a_essence_offset may be less than to klv.offset (C0023S01.mxf) */
mxf->current_partition->essence_offset = op1a_essence_offset;
}
}
if (IS_KLV_KEY(klv.key, mxf_system_item_key)) {
mxf->system_item = 1;
}
@ -1481,6 +1547,9 @@ static int mxf_read_header(AVFormatContext *s, AVFormatParameters *ap)
return AVERROR_INVALIDDATA;
}
avio_seek(s->pb, mxf->essence_offset, SEEK_SET);
mxf_compute_essence_containers(mxf);
return mxf_parse_structural_metadata(mxf);
}