Andreas Rheinhardt:
> Up until now, SeekEntries were already added before
> start_ebml_master_crc32() was even called and before we were actually
> sure that we really write the element the SeekHead references; after
> all, we might also error out later; and given that the allocations
> implicit in dynamic buffers should be checked, end_ebml_master_crc32()
> will eventually have to return errors itself, so that it is the right
> place to add SeekHead entries.
>
> The earlier behaviour is of course a remnant of the time in which
> start_ebml_master_crc32() really did output something, so that the
> position before start_ebml_master_crc32() needed to be recorded.
> Erroring out later is also not as dangerous as it seems because in
> this case no SeekHead will be written (if it happened when writing
> the header, the whole muxing process would abort; if it happened
> when writing the trailer (when writing chapters not available initially),
> writing the trailer would be aborted and no SeekHead containing the
> bogus chapter entry would be written).
>
> This commit does not change the way the SeekEntries are added for those
> elements that are output preliminarily; this is so because the SeekHead
> is written before those elements are finally output and doing it
> otherwise would increase the amount of seeks.
>
> Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@gmail.com>
> ---
> libavformat/matroskaenc.c | 64 ++++++++++++++++++++-------------------
> 1 file changed, 33 insertions(+), 31 deletions(-)
>
> diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
> index a1b613290c..b50fd8dd9b 100644
> --- a/libavformat/matroskaenc.c
> +++ b/libavformat/matroskaenc.c
> @@ -349,6 +349,17 @@ static void end_ebml_master(AVIOContext *pb, ebml_master
> master)
> avio_seek(pb, pos, SEEK_SET);
> }
>
> +static void mkv_add_seekhead_entry(MatroskaMuxContext *mkv, uint32_t
> elementid,
> + uint64_t filepos)
> +{
> + mkv_seekhead *seekhead = &mkv->seekhead;
> +
> + av_assert1(seekhead->num_entries < MAX_SEEKHEAD_ENTRIES);
> +
> + seekhead->entries[seekhead->num_entries].elementid = elementid;
> + seekhead->entries[seekhead->num_entries++].segmentpos = filepos -
> mkv->segment_offset;
> +}
> +
> static int start_ebml_master_crc32(AVIOContext **dyn_cp, MatroskaMuxContext
> *mkv)
> {
> int ret;
> @@ -364,11 +375,15 @@ static int start_ebml_master_crc32(AVIOContext
> **dyn_cp, MatroskaMuxContext *mkv
>
> static void end_ebml_master_crc32(AVIOContext *pb, AVIOContext **dyn_cp,
> MatroskaMuxContext *mkv, uint32_t id,
> - int length_size, int keep_buffer)
> + int length_size, int keep_buffer,
> + int add_seekentry)
> {
> uint8_t *buf, crc[4];
> int size, skip = 0;
>
> + if (add_seekentry)
> + mkv_add_seekhead_entry(mkv, id, avio_tell(pb));
> +
> put_ebml_id(pb, id);
> size = avio_get_dyn_buf(*dyn_cp, &buf);
> put_ebml_length(pb, size, length_size);
> @@ -441,17 +456,6 @@ static void mkv_start_seekhead(MatroskaMuxContext *mkv,
> AVIOContext *pb)
> put_ebml_void(pb, mkv->seekhead.reserved_size);
> }
>
> -static void mkv_add_seekhead_entry(MatroskaMuxContext *mkv, uint32_t
> elementid,
> - uint64_t filepos)
> -{
> - mkv_seekhead *seekhead = &mkv->seekhead;
> -
> - av_assert1(seekhead->num_entries < MAX_SEEKHEAD_ENTRIES);
> -
> - seekhead->entries[seekhead->num_entries].elementid = elementid;
> - seekhead->entries[seekhead->num_entries++].segmentpos = filepos -
> mkv->segment_offset;
> -}
> -
> /**
> * Write the SeekHead to the file at the location reserved for it
> * and seek to destpos afterwards. When error_on_seek_failure
> @@ -489,7 +493,7 @@ static int mkv_write_seekhead(AVIOContext *pb,
> MatroskaMuxContext *mkv,
> put_ebml_uint(dyn_cp, MATROSKA_ID_SEEKPOSITION, entry->segmentpos);
> end_ebml_master(dyn_cp, seekentry);
> }
> - end_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_SEEKHEAD, 0, 0);
> + end_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_SEEKHEAD, 0, 0, 0);
>
> remaining = seekhead->filepos + seekhead->reserved_size - avio_tell(pb);
> put_ebml_void(pb, remaining);
> @@ -1421,7 +1425,8 @@ static int mkv_write_tracks(AVFormatContext *s)
> end_ebml_master_crc32_preliminary(pb, mkv->tracks_bc,
> MATROSKA_ID_TRACKS,
> &mkv->tracks_pos);
> else
> - end_ebml_master_crc32(pb, &mkv->tracks_bc, mkv, MATROSKA_ID_TRACKS,
> 0, 0);
> + end_ebml_master_crc32(pb, &mkv->tracks_bc, mkv,
> + MATROSKA_ID_TRACKS, 0, 0, 0);
>
> return 0;
> }
> @@ -1443,8 +1448,6 @@ static int mkv_write_chapters(AVFormatContext *s)
> break;
> }
>
In my private branch, these six patches are based upon my earlier
patchset, in particular [1]. It looked as if the new six patches applied
nevertheless on master as they don't touch put_flac_codecpriv(); yet I
was wrong: I forgot about these few lines above. So don't be surprised
that patchwork reports "failed to apply patch". Sorry.
- Andreas
[1]: http://ffmpeg.org/pipermail/ffmpeg-devel/2020-April/261540.html
> - mkv_add_seekhead_entry(mkv, MATROSKA_ID_CHAPTERS, avio_tell(pb));
> -
> ret = start_ebml_master_crc32(&dyn_cp, mkv);
> if (ret < 0)
> return ret;
> @@ -1481,7 +1484,7 @@ static int mkv_write_chapters(AVFormatContext *s)
> end_ebml_master(dyn_cp, chapteratom);
> }
> end_ebml_master(dyn_cp, editionentry);
> - end_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_CHAPTERS, 0, 0);
> + end_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_CHAPTERS, 0, 0, 1);
>
> mkv->wrote_chapters = 1;
> return 0;
> @@ -1682,7 +1685,8 @@ static int mkv_write_tags(AVFormatContext *s)
> end_ebml_master_crc32_preliminary(s->pb, mkv->tags_bc,
> MATROSKA_ID_TAGS,
> &mkv->tags_pos);
> else
> - end_ebml_master_crc32(s->pb, &mkv->tags_bc, mkv,
> MATROSKA_ID_TAGS, 0, 0);
> + end_ebml_master_crc32(s->pb, &mkv->tags_bc, mkv,
> + MATROSKA_ID_TAGS, 0, 0, 0);
> }
> return 0;
> }
> @@ -1713,8 +1717,6 @@ static int mkv_write_attachments(AVFormatContext *s)
> if (!mkv->nb_attachments)
> return 0;
>
> - mkv_add_seekhead_entry(mkv, MATROSKA_ID_ATTACHMENTS, avio_tell(pb));
> -
> ret = start_ebml_master_crc32(&dyn_cp, mkv);
> if (ret < 0)
> return ret;
> @@ -1746,7 +1748,7 @@ static int mkv_write_attachments(AVFormatContext *s)
> put_ebml_uid(dyn_cp, MATROSKA_ID_FILEUID, track->uid);
> end_ebml_master(dyn_cp, attached_file);
> }
> - end_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_ATTACHMENTS, 0, 0);
> + end_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_ATTACHMENTS, 0, 0,
> 1);
>
> return 0;
> }
> @@ -1868,7 +1870,8 @@ static int mkv_write_header(AVFormatContext *s)
> end_ebml_master_crc32_preliminary(s->pb, mkv->info_bc,
> MATROSKA_ID_INFO, &mkv->info_pos);
> else
> - end_ebml_master_crc32(s->pb, &mkv->info_bc, mkv, MATROSKA_ID_INFO,
> 0, 0);
> + end_ebml_master_crc32(s->pb, &mkv->info_bc, mkv,
> + MATROSKA_ID_INFO, 0, 0, 0);
> pb = s->pb;
>
> ret = mkv_write_tracks(s);
> @@ -2153,7 +2156,8 @@ static void mkv_end_cluster(AVFormatContext *s)
> {
> MatroskaMuxContext *mkv = s->priv_data;
>
> - end_ebml_master_crc32(s->pb, &mkv->cluster_bc, mkv, MATROSKA_ID_CLUSTER,
> 0, 1);
> + end_ebml_master_crc32(s->pb, &mkv->cluster_bc, mkv,
> + MATROSKA_ID_CLUSTER, 0, 1, 0);
> if (!mkv->have_video) {
> for (unsigned i = 0; i < s->nb_streams; i++)
> mkv->tracks[i].has_cue = 0;
> @@ -2447,7 +2451,7 @@ static int mkv_write_trailer(AVFormatContext *s)
>
> if (mkv->cluster_bc) {
> end_ebml_master_crc32(pb, &mkv->cluster_bc, mkv,
> - MATROSKA_ID_CLUSTER, 0, 0);
> + MATROSKA_ID_CLUSTER, 0, 0, 0);
> }
>
> ret = mkv_write_chapters(s);
> @@ -2463,7 +2467,6 @@ static int mkv_write_trailer(AVFormatContext *s)
> if (mkv->cues.num_entries) {
> AVIOContext *cues = NULL;
> uint64_t size;
> - int64_t cuespos = endpos;
> int length_size = 0;
>
> ret = start_ebml_master_crc32(&cues, mkv);
> @@ -2490,7 +2493,6 @@ static int mkv_write_trailer(AVFormatContext *s)
> ffio_free_dyn_buf(&cues);
> goto after_cues;
> } else {
> - cuespos = mkv->cues_pos;
> if ((ret64 = avio_seek(pb, mkv->cues_pos, SEEK_SET)) <
> 0) {
> ffio_free_dyn_buf(&cues);
> return ret64;
> @@ -2506,9 +2508,8 @@ static int mkv_write_trailer(AVFormatContext *s)
> }
> }
> }
> - mkv_add_seekhead_entry(mkv, MATROSKA_ID_CUES, cuespos);
> end_ebml_master_crc32(pb, &cues, mkv, MATROSKA_ID_CUES,
> - length_size, 0);
> + length_size, 0, 1);
> if (mkv->reserve_cues_space) {
> if (size < mkv->reserve_cues_space)
> put_ebml_void(pb, mkv->reserve_cues_space - size);
> @@ -2525,13 +2526,13 @@ static int mkv_write_trailer(AVFormatContext *s)
> av_log(s, AV_LOG_DEBUG, "end duration = %" PRIu64 "\n",
> mkv->duration);
> avio_seek(mkv->info_bc, mkv->duration_offset, SEEK_SET);
> put_ebml_float(mkv->info_bc, MATROSKA_ID_DURATION, mkv->duration);
> - end_ebml_master_crc32(pb, &mkv->info_bc, mkv, MATROSKA_ID_INFO, 0,
> 0);
> + end_ebml_master_crc32(pb, &mkv->info_bc, mkv, MATROSKA_ID_INFO, 0,
> 0, 0);
>
> if (mkv->tracks_bc) {
> // write Tracks master
> avio_seek(pb, mkv->tracks_pos, SEEK_SET);
> end_ebml_master_crc32(pb, &mkv->tracks_bc, mkv,
> - MATROSKA_ID_TRACKS, 0, 0);
> + MATROSKA_ID_TRACKS, 0, 0, 0);
> }
>
> // update stream durations
> @@ -2559,7 +2560,8 @@ static int mkv_write_trailer(AVFormatContext *s)
> }
>
> avio_seek(pb, mkv->tags_pos, SEEK_SET);
> - end_ebml_master_crc32(pb, &mkv->tags_bc, mkv, MATROSKA_ID_TAGS,
> 0, 0);
> + end_ebml_master_crc32(pb, &mkv->tags_bc, mkv,
> + MATROSKA_ID_TAGS, 0, 0, 0);
> }
>
> avio_seek(pb, endpos, SEEK_SET);
>
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