[FFmpeg-devel] [PATCH 3/4] matroska: redo seekhead handling
wm4
nfxjfg at googlemail.com
Mon Feb 9 20:39:00 CET 2015
In particular, this reads chained seekheads. This makes seeking faster
in files which have the index indirectly linked through 2 seekheads.
As a side-effect, this warns when reading level-1 (toplevel) elements
multiple times (other than seekheads, clusters, and void/crc). Such
elements are not valid and likely break everything.
---
libavformat/matroskadec.c | 125 ++++++++++++++++++++++++++++++++--------------
1 file changed, 88 insertions(+), 37 deletions(-)
diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index 2957536..7af7845 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -71,6 +71,7 @@ typedef enum {
EBML_UTF8,
EBML_BIN,
EBML_NEST,
+ EBML_LEVEL1,
EBML_PASS,
EBML_STOP,
EBML_SINT,
@@ -253,6 +254,12 @@ typedef struct {
} MatroskaCluster;
typedef struct {
+ uint64_t id;
+ uint64_t pos;
+ int parsed;
+} MatroskaLevel1Element;
+
+typedef struct {
AVFormatContext *ctx;
/* EBML stuff */
@@ -290,6 +297,10 @@ typedef struct {
/* File has a CUES element, but we defer parsing until it is needed. */
int cues_parsing_deferred;
+ /* Level1 elements and whether they were read yet */
+ MatroskaLevel1Element level1_elems[64];
+ int num_level1_elems;
+
int current_cluster_num_blocks;
int64_t current_cluster_pos;
MatroskaCluster current_cluster;
@@ -513,13 +524,13 @@ static EbmlSyntax matroska_seekhead[] = {
};
static EbmlSyntax matroska_segment[] = {
- { MATROSKA_ID_INFO, EBML_NEST, 0, 0, { .n = matroska_info } },
- { MATROSKA_ID_TRACKS, EBML_NEST, 0, 0, { .n = matroska_tracks } },
- { MATROSKA_ID_ATTACHMENTS, EBML_NEST, 0, 0, { .n = matroska_attachments } },
- { MATROSKA_ID_CHAPTERS, EBML_NEST, 0, 0, { .n = matroska_chapters } },
- { MATROSKA_ID_CUES, EBML_NEST, 0, 0, { .n = matroska_index } },
- { MATROSKA_ID_TAGS, EBML_NEST, 0, 0, { .n = matroska_tags } },
- { MATROSKA_ID_SEEKHEAD, EBML_NEST, 0, 0, { .n = matroska_seekhead } },
+ { MATROSKA_ID_INFO, EBML_LEVEL1, 0, 0, { .n = matroska_info } },
+ { MATROSKA_ID_TRACKS, EBML_LEVEL1, 0, 0, { .n = matroska_tracks } },
+ { MATROSKA_ID_ATTACHMENTS, EBML_LEVEL1, 0, 0, { .n = matroska_attachments } },
+ { MATROSKA_ID_CHAPTERS, EBML_LEVEL1, 0, 0, { .n = matroska_chapters } },
+ { MATROSKA_ID_CUES, EBML_LEVEL1, 0, 0, { .n = matroska_index } },
+ { MATROSKA_ID_TAGS, EBML_LEVEL1, 0, 0, { .n = matroska_tags } },
+ { MATROSKA_ID_SEEKHEAD, EBML_LEVEL1, 0, 0, { .n = matroska_seekhead } },
{ MATROSKA_ID_CLUSTER, EBML_STOP },
{ 0 }
};
@@ -919,6 +930,42 @@ static int ebml_parse_nest(MatroskaDemuxContext *matroska, EbmlSyntax *syntax,
return res;
}
+/*
+ * Allocate and return the entry for the level1 element with the given ID. If
+ * an entry already exists, return the existing entry.
+ */
+static MatroskaLevel1Element *matroska_find_level1_elem(MatroskaDemuxContext *matroska,
+ uint32_t id)
+{
+ int i;
+ MatroskaLevel1Element *elem;
+
+ // Some files link to all clusters; useless.
+ if (id == MATROSKA_ID_CLUSTER)
+ return NULL;
+
+ // There can be multiple seekheads.
+ if (id != MATROSKA_ID_SEEKHEAD) {
+ for (i = 0; i < matroska->num_level1_elems; i++) {
+ if (matroska->level1_elems[i].id == id)
+ return &matroska->level1_elems[i];
+ }
+ }
+
+ // Only a completely broken file would have more elements.
+ // It also provides a low-effort way to escape from circular seekheads
+ // (every iteration will add a level1 entry).
+ if (matroska->num_level1_elems >= FF_ARRAY_ELEMS(matroska->level1_elems)) {
+ av_log(matroska->ctx, AV_LOG_ERROR, "Too many level1 elements or circular seekheads.\n");
+ return NULL;
+ }
+
+ elem = &matroska->level1_elems[matroska->num_level1_elems++];
+ *elem = (MatroskaLevel1Element){.id = id};
+
+ return elem;
+}
+
static int ebml_parse_elem(MatroskaDemuxContext *matroska,
EbmlSyntax *syntax, void *data)
{
@@ -937,6 +984,7 @@ static int ebml_parse_elem(MatroskaDemuxContext *matroska,
uint64_t length;
int res;
void *newelem;
+ MatroskaLevel1Element *level1_elem;
data = (char *) data + syntax->data_offset;
if (syntax->list_elem_size) {
@@ -979,11 +1027,20 @@ static int ebml_parse_elem(MatroskaDemuxContext *matroska,
case EBML_BIN:
res = ebml_read_binary(pb, length, data);
break;
+ case EBML_LEVEL1:
case EBML_NEST:
if ((res = ebml_read_master(matroska, length)) < 0)
return res;
if (id == MATROSKA_ID_SEGMENT)
matroska->segment_start = avio_tell(matroska->ctx->pb);
+ if (id == MATROSKA_ID_CUES)
+ matroska->cues_parsing_deferred = 0;
+ if (syntax->type == EBML_LEVEL1 &&
+ (level1_elem = matroska_find_level1_elem(matroska, syntax->id))) {
+ if (level1_elem->parsed)
+ av_log(matroska->ctx, AV_LOG_ERROR, "Duplicate element\n");
+ level1_elem->parsed = 1;
+ }
return ebml_parse_nest(matroska, syntax->def.n, data);
case EBML_PASS:
return ebml_parse_id(matroska, syntax->def.n, id, data);
@@ -1014,6 +1071,7 @@ static void ebml_free(EbmlSyntax *syntax, void *data)
case EBML_BIN:
av_freep(&((EbmlBin *) data_off)->data);
break;
+ case EBML_LEVEL1:
case EBML_NEST:
if (syntax[i].list_elem_size) {
EbmlList *list = data_off;
@@ -1299,24 +1357,17 @@ static void matroska_convert_tags(AVFormatContext *s)
}
static int matroska_parse_seekhead_entry(MatroskaDemuxContext *matroska,
- int idx)
+ uint64_t pos)
{
- EbmlList *seekhead_list = &matroska->seekhead;
uint32_t level_up = matroska->level_up;
uint32_t saved_id = matroska->current_id;
- MatroskaSeekhead *seekhead = seekhead_list->elem;
int64_t before_pos = avio_tell(matroska->ctx->pb);
MatroskaLevel level;
int64_t offset;
int ret = 0;
- if (idx >= seekhead_list->nb_elem ||
- seekhead[idx].id == MATROSKA_ID_SEEKHEAD ||
- seekhead[idx].id == MATROSKA_ID_CLUSTER)
- return 0;
-
/* seek */
- offset = seekhead[idx].pos + matroska->segment_start;
+ offset = pos + matroska->segment_start;
if (avio_seek(matroska->ctx->pb, offset, SEEK_SET) == offset) {
/* We don't want to lose our seekhead level, so we add
* a dummy. This is a crude hack. */
@@ -1353,37 +1404,35 @@ static int matroska_parse_seekhead_entry(MatroskaDemuxContext *matroska,
static void matroska_execute_seekhead(MatroskaDemuxContext *matroska)
{
EbmlList *seekhead_list = &matroska->seekhead;
- int64_t before_pos = avio_tell(matroska->ctx->pb);
int i;
- int nb_elem;
// we should not do any seeking in the streaming case
if (!matroska->ctx->pb->seekable ||
(matroska->ctx->flags & AVFMT_FLAG_IGNIDX))
return;
- // do not read entries that are added while parsing seekhead entries
- nb_elem = seekhead_list->nb_elem;
+ for (i = 0; i < seekhead_list->nb_elem; i++) {
+ MatroskaSeekhead *seekheads = seekhead_list->elem;
+ uint32_t id = seekheads[i].id;
+ uint64_t pos = seekheads[i].pos;
- for (i = 0; i < nb_elem; i++) {
- MatroskaSeekhead *seekhead = seekhead_list->elem;
- if (seekhead[i].pos <= before_pos)
+ MatroskaLevel1Element *elem = matroska_find_level1_elem(matroska, id);
+ if (!elem || elem->parsed)
continue;
+ elem->pos = pos;
+
// defer cues parsing until we actually need cue data.
- if (seekhead[i].id == MATROSKA_ID_CUES) {
- matroska->cues_parsing_deferred = 1;
+ if (id == MATROSKA_ID_CUES)
continue;
- }
- if (matroska_parse_seekhead_entry(matroska, i) < 0) {
+ if (matroska_parse_seekhead_entry(matroska, pos) < 0) {
// mark index as broken
matroska->cues_parsing_deferred = -1;
break;
}
- }
- if (nb_elem != seekhead_list->nb_elem) {
- avpriv_request_sample(matroska->ctx, "recursive SeekHead elements");
+
+ elem->parsed = 1;
}
}
@@ -1417,17 +1466,18 @@ static void matroska_add_index_entries(MatroskaDemuxContext *matroska)
}
static void matroska_parse_cues(MatroskaDemuxContext *matroska) {
- EbmlList *seekhead_list = &matroska->seekhead;
- MatroskaSeekhead *seekhead = seekhead_list->elem;
int i;
- for (i = 0; i < seekhead_list->nb_elem; i++)
- if (seekhead[i].id == MATROSKA_ID_CUES)
+ for (i = 0; i < matroska->num_level1_elems; i++) {
+ MatroskaLevel1Element *elem = &matroska->level1_elems[i];
+ if (elem->id == MATROSKA_ID_CUES && !elem->parsed) {
+ if (matroska_parse_seekhead_entry(matroska, elem->pos) < 0)
+ matroska->cues_parsing_deferred = -1;
+ elem->parsed = 1;
break;
- av_assert1(i <= seekhead_list->nb_elem);
+ }
+ }
- if (matroska_parse_seekhead_entry(matroska, i) < 0)
- matroska->cues_parsing_deferred = -1;
matroska_add_index_entries(matroska);
}
@@ -1957,6 +2007,7 @@ static int matroska_read_header(AVFormatContext *s)
int i, j, res;
matroska->ctx = s;
+ matroska->cues_parsing_deferred = 1;
/* First read the EBML header. */
if (ebml_parse(matroska, ebml_syntax, &ebml) ||
--
2.1.4
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