From 7e9b7cdc9f7c030b7adc4440ce6dba8246b7f33d Mon Sep 17 00:00:00 2001 From: Dale Curtis Date: Mon, 28 Aug 2017 12:37:09 -0700 Subject: [PATCH] [mov] Avoid O(n^2) memmove() operations when inserting ctts entries. A previous patch to ctts reads added support for inserting ctts entries in sample order. If an insert happens in the middle of existing ctts entries, we would shift 1 entry at a time to make room. This patch attempts to shift entries only once based on the expected ctts entry count. The caveat is that av_add_index_entry() may fail and in such a case we need to recover the gap in ctts entries. This is done in best effort fashion, although I'm not confident this will always work. I don't have any concrete examples, just a vague worry this can lead to ctts desync when index insertion fails. Signed-off-by: Dale Curtis --- libavformat/mov.c | 34 ++++++++++++++++++++++++++-------- 1 file changed, 26 insertions(+), 8 deletions(-) diff --git a/libavformat/mov.c b/libavformat/mov.c index 876f48d912..91c956431f 100644 --- a/libavformat/mov.c +++ b/libavformat/mov.c @@ -4263,6 +4263,7 @@ static int mov_read_trun(MOVContext *c, AVIOContext *pb, MOVAtom atom) uint64_t offset; int64_t dts; int data_offset = 0; + int expected_ctts_count, old_ctts_count, first_ctts_index = -1; unsigned entries, first_sample_flags = frag->flags; int flags, distance, i; @@ -4306,6 +4307,9 @@ static int mov_read_trun(MOVContext *c, AVIOContext *pb, MOVAtom atom) } if ((uint64_t)entries+sc->ctts_count >= UINT_MAX/sizeof(*sc->ctts_data)) return AVERROR_INVALIDDATA; + old_ctts_count = sc->ctts_count; + expected_ctts_count = sc->ctts_count + entries; + if (flags & MOV_TRUN_DATA_OFFSET) data_offset = avio_rb32(pb); if (flags & MOV_TRUN_FIRST_SAMPLE_FLAGS) first_sample_flags = avio_rb32(pb); dts = sc->track_end - sc->time_offset; @@ -4361,9 +4365,10 @@ static int mov_read_trun(MOVContext *c, AVIOContext *pb, MOVAtom atom) ctts_index = av_add_index_entry(st, offset, dts, sample_size, distance, keyframe ? AVINDEX_KEYFRAME : 0); if (ctts_index >= 0 && old_nb_index_entries < st->nb_index_entries) { - unsigned int size_needed = st->nb_index_entries * sizeof(*sc->ctts_data); + unsigned int size_needed = expected_ctts_count * sizeof(*sc->ctts_data); unsigned int request_size = size_needed > sc->ctts_allocated_size ? FFMAX(size_needed, 2 * sc->ctts_allocated_size) : size_needed; + av_assert0(ctts_index < expected_ctts_count); ctts_data = av_fast_realloc(sc->ctts_data, &sc->ctts_allocated_size, request_size); if (!ctts_data) { av_freep(&sc->ctts_data); @@ -4371,14 +4376,16 @@ static int mov_read_trun(MOVContext *c, AVIOContext *pb, MOVAtom atom) } sc->ctts_data = ctts_data; - if (ctts_index != old_nb_index_entries) { - memmove(sc->ctts_data + ctts_index + 1, sc->ctts_data + ctts_index, + if (first_ctts_index < 0 && ctts_index != old_nb_index_entries) { + memmove(sc->ctts_data + entries, sc->ctts_data + ctts_index, sizeof(*sc->ctts_data) * (sc->ctts_count - ctts_index)); - if (ctts_index <= sc->current_sample) { - // if we inserted a new item before the current sample, move the - // counter ahead so it is still pointing to the same sample. - sc->current_sample++; - } + first_ctts_index = ctts_index; + } + + if (ctts_index != old_nb_index_entries && ctts_index <= sc->current_sample) { + // if we inserted a new item before the current sample, move the + // counter ahead so it is still pointing to the same sample. + sc->current_sample++; } sc->ctts_data[ctts_index].count = 1; @@ -4399,6 +4406,17 @@ static int mov_read_trun(MOVContext *c, AVIOContext *pb, MOVAtom atom) sc->nb_frames_for_fps ++; } + // Some error occurred while inserting ctts entries. We need to shift back + // the entries we expected to fill to remove the gap. + if (expected_ctts_count != sc->ctts_count && first_ctts_index >= 0) { + int actual_entry_count = sc->ctts_count - old_ctts_count; + int actual_entry_end = first_ctts_index + actual_entry_count; + av_log(c->fc, AV_LOG_ERROR, "Failed to add index entry - rewinding ctts table gap\n"); + av_assert0(expected_ctts_count > sc->ctts_count); + memmove(sc->ctts_data + actual_entry_end, sc->ctts_data + entries, + sizeof(*sc->ctts_data) * (sc->ctts_count - actual_entry_end)); + } + if (pb->eof_reached) return AVERROR_EOF; -- 2.14.1.342.g6490525c54-goog