From e04a24e70148e330bcdcfd7c049acbe1a821398f Mon Sep 17 00:00:00 2001 From: Andreas Rheinhardt Date: Sat, 20 Apr 2019 01:41:05 +0200 Subject: avformat/matroskaenc: Avoid seeking when writing level 1 elements Up until now, the writing process for level 1 elements (those elements for which CRC-32 elements are written by default) was this in case the output was seekable: Write the EBML ID, write an "unkown length" EBML number of the desired length, then write the element into a dynamic buffer, then write the dynamic buffer (after possible calculation and writing of the CRC-element), then seek back to the size element and overwrite the unknown-size element with the real size. The seeking and overwriting part has been eliminated by not writing the size initially. Signed-off-by: Andreas Rheinhardt Signed-off-by: James Almer --- libavformat/matroskaenc.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c index 0be3341..2875552 100644 --- a/libavformat/matroskaenc.c +++ b/libavformat/matroskaenc.c @@ -58,8 +58,9 @@ #include "libavcodec/internal.h" typedef struct ebml_master { - int64_t pos; ///< absolute offset in the file where the master's elements start - int sizebytes; ///< how many bytes were reserved for the size + int64_t pos; ///< absolute offset in the containing AVIOContext where the size field starts + ///< for level 1 elements or else where the master's elements start + int sizebytes; ///< how many bytes were reserved/shall be used for the size } ebml_master; typedef struct mkv_seekhead_entry { @@ -316,6 +317,7 @@ static ebml_master start_ebml_master(AVIOContext *pb, uint32_t elementid, uint64_t expectedsize) { int bytes = expectedsize ? ebml_num_size(expectedsize) : 8; + put_ebml_id(pb, elementid); put_ebml_size_unknown(pb, bytes); return (ebml_master) {avio_tell(pb), bytes }; @@ -340,7 +342,10 @@ static int start_ebml_master_crc32(AVIOContext *pb, AVIOContext **dyn_cp, Matros return ret; if (pb->seekable & AVIO_SEEKABLE_NORMAL) { - *master = start_ebml_master(pb, elementid, expectedsize); + int bytes = expectedsize ? ebml_num_size(expectedsize) : 8; + + put_ebml_id(pb, elementid); + *master = (ebml_master) { avio_tell(pb), bytes }; if (mkv->write_crc) put_ebml_void(*dyn_cp, 6); /* Reserve space for CRC32 so position/size calculations using avio_tell() take it into account */ } else @@ -357,13 +362,13 @@ static void end_ebml_master_crc32(AVIOContext *pb, AVIOContext **dyn_cp, Matrosk if (pb->seekable & AVIO_SEEKABLE_NORMAL) { size = avio_close_dyn_buf(*dyn_cp, &buf); + put_ebml_num(pb, size, master.sizebytes); if (mkv->write_crc) { skip = 6; /* Skip reserved 6-byte long void element from the dynamic buffer. */ AV_WL32(crc, av_crc(av_crc_get_table(AV_CRC_32_IEEE_LE), UINT32_MAX, buf + skip, size - skip) ^ UINT32_MAX); put_ebml_binary(pb, EBML_ID_CRC32, crc, sizeof(crc)); } avio_write(pb, buf + skip, size - skip); - end_ebml_master(pb, master); } else { end_ebml_master(*dyn_cp, master); size = avio_close_dyn_buf(*dyn_cp, &buf); @@ -383,8 +388,8 @@ static void end_ebml_master_crc32_preliminary(AVIOContext *pb, AVIOContext **dyn uint8_t *buf; int size = avio_get_dyn_buf(*dyn_cp, &buf); + put_ebml_num(pb, size, master.sizebytes); avio_write(pb, buf, size); - end_ebml_master(pb, master); } static void put_xiph_size(AVIOContext *pb, int size) -- cgit v1.1