lavf: add AVFMT_FLAG_BITEXACT.

Use it instead of checking CODEC_FLAG_BITEXACT in the first stream's
codec context.

Using codec options inside lavf is fragile and can easily break when the
muxing codec context is not the encoding context.

9 files changed, 28 insertions, 12 deletions

diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index 1ce3eba675..8d134a0945 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -1004,6 +1004,13 @@ typedef struct AVFormatContext {
 #define AVFMT_FLAG_CUSTOM_IO    0x0080 ///< The caller has supplied a custom AVIOContext, don't avio_close() it.
 #define AVFMT_FLAG_DISCARD_CORRUPT  0x0100 ///< Discard frames marked corrupted
 #define AVFMT_FLAG_FLUSH_PACKETS    0x0200 ///< Flush the AVIOContext every packet.
+/**
+ * When muxing, try to avoid writing any random/volatile data to the output.
+ * This includes any random IDs, real-time timestamps/dates, muxer version, etc.
+ *
+ * This flag is mainly intended for testing.
+ */
+#define AVFMT_FLAG_BITEXACT         0x0400
 
     /**
      * Maximum size of the data read from input for determining
diff --git a/libavformat/flacenc.c b/libavformat/flacenc.c
index 83ddf441e0..8a23163772 100644
--- a/libavformat/flacenc.c
+++ b/libavformat/flacenc.c
@@ -84,7 +84,7 @@ static int flac_write_header(struct AVFormatContext *s)
         return ret;
 
     ret = flac_write_block_comment(s->pb, &s->metadata, 0,
-                                   codec->flags & CODEC_FLAG_BITEXACT);
+                                   s->flags & AVFMT_FLAG_BITEXACT);
     if (ret)
         return ret;
 
diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index d2e3ae4979..c71b32d411 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -970,7 +970,7 @@ static int mkv_write_header(AVFormatContext *s)
     put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, 1000000);
     if ((tag = av_dict_get(s->metadata, "title", NULL, 0)))
         put_ebml_string(pb, MATROSKA_ID_TITLE, tag->value);
-    if (!(s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT)) {
+    if (!(s->flags & AVFMT_FLAG_BITEXACT)) {
         uint32_t segment_uid[4];
         AVLFG lfg;
 
diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 73fbddc451..9087438998 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -2024,7 +2024,7 @@ static int mov_write_udta_tag(AVIOContext *pb, MOVMuxContext *mov,
     uint8_t *buf;
 
     for (i = 0; i < s->nb_streams; i++)
-        if (mov->tracks[i].enc->flags & CODEC_FLAG_BITEXACT) {
+        if (s->flags & AVFMT_FLAG_BITEXACT) {
             return 0;
         }
 
diff --git a/libavformat/mux.c b/libavformat/mux.c
index 59f9c42cf1..33257ea147 100644
--- a/libavformat/mux.c
+++ b/libavformat/mux.c
@@ -149,6 +149,11 @@ static int init_muxer(AVFormatContext *s, AVDictionary **options)
     if ((ret = av_opt_set_dict(s, &tmp)) < 0)
         goto fail;
 
+#if FF_API_LAVF_BITEXACT
+    if (s->nb_streams && s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT)
+        s->flags |= AVFMT_FLAG_BITEXACT;
+#endif
+
     // some sanity checks
     if (s->nb_streams == 0 && !(of->flags & AVFMT_NOSTREAMS)) {
         av_log(s, AV_LOG_ERROR, "no streams\n");
@@ -252,7 +257,7 @@ static int init_muxer(AVFormatContext *s, AVDictionary **options)
     }
 
     /* set muxer identification string */
-    if (s->nb_streams && !(s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT)) {
+    if (!(s->flags & AVFMT_FLAG_BITEXACT)) {
         av_dict_set(&s->metadata, "encoder", LIBAVFORMAT_IDENT, 0);
     }
 
diff --git a/libavformat/mxfenc.c b/libavformat/mxfenc.c
index 4fd5687beb..66beec2940 100644
--- a/libavformat/mxfenc.c
+++ b/libavformat/mxfenc.c
@@ -507,7 +507,7 @@ static void mxf_write_identification(AVFormatContext *s)
     mxf_write_metadata_key(pb, 0x013000);
     PRINT_KEY(s, "identification key", pb->buf_ptr - 16);
 
-    version = s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT ?
+    version = s->flags & AVFMT_FLAG_BITEXACT ?
         "0.0.0" : AV_STRINGIFY(LIBAVFORMAT_VERSION);
     length = 84 + (strlen(company)+strlen(product)+strlen(version))*2; // utf-16
     klv_encode_ber_length(pb, length);
@@ -1512,7 +1512,7 @@ static int mxf_write_header(AVFormatContext *s)
         mxf->essence_container_count = 1;
     }
 
-    if (!(s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT))
+    if (!(s->flags & AVFMT_FLAG_BITEXACT))
         mxf_gen_umid(s);
 
     for (i = 0; i < s->nb_streams; i++) {
diff --git a/libavformat/oggenc.c b/libavformat/oggenc.c
index fd102c86ad..c52368dde3 100644
--- a/libavformat/oggenc.c
+++ b/libavformat/oggenc.c
@@ -425,7 +425,7 @@ static int ogg_write_header(AVFormatContext *s)
         oggstream = av_mallocz(sizeof(*oggstream));
         oggstream->page.stream_index = i;
 
-        if (!(st->codec->flags & CODEC_FLAG_BITEXACT))
+        if (!(s->flags & AVFMT_FLAG_BITEXACT))
             do {
                 serial_num = av_get_random_seed();
                 for (j = 0; j < i; j++) {
@@ -439,7 +439,7 @@ static int ogg_write_header(AVFormatContext *s)
         st->priv_data = oggstream;
         if (st->codec->codec_id == AV_CODEC_ID_FLAC) {
             int err = ogg_build_flac_headers(st->codec, oggstream,
-                                             st->codec->flags & CODEC_FLAG_BITEXACT,
+                                             s->flags & AVFMT_FLAG_BITEXACT,
                                              &s->metadata);
             if (err) {
                 av_log(s, AV_LOG_ERROR, "Error writing FLAC headers\n");
@@ -448,7 +448,7 @@ static int ogg_write_header(AVFormatContext *s)
             }
         } else if (st->codec->codec_id == AV_CODEC_ID_SPEEX) {
             int err = ogg_build_speex_headers(st->codec, oggstream,
-                                              st->codec->flags & CODEC_FLAG_BITEXACT,
+                                              s->flags & AVFMT_FLAG_BITEXACT,
                                               &s->metadata);
             if (err) {
                 av_log(s, AV_LOG_ERROR, "Error writing Speex headers\n");
@@ -457,7 +457,7 @@ static int ogg_write_header(AVFormatContext *s)
             }
         } else if (st->codec->codec_id == AV_CODEC_ID_OPUS) {
             int err = ogg_build_opus_headers(st->codec, oggstream,
-                                             st->codec->flags & CODEC_FLAG_BITEXACT,
+                                             s->flags & AVFMT_FLAG_BITEXACT,
                                              &s->metadata);
             if (err) {
                 av_log(s, AV_LOG_ERROR, "Error writing Opus headers\n");
@@ -478,7 +478,7 @@ static int ogg_write_header(AVFormatContext *s)
                 return -1;
             }
 
-            p = ogg_write_vorbiscomment(7, st->codec->flags & CODEC_FLAG_BITEXACT,
+            p = ogg_write_vorbiscomment(7, s->flags & AVFMT_FLAG_BITEXACT,
                                         &oggstream->header_len[1], &s->metadata,
                                         framing_bit);
             oggstream->header[1] = p;
diff --git a/libavformat/options_table.h b/libavformat/options_table.h
index cc84e1c02f..70194202d7 100644
--- a/libavformat/options_table.h
+++ b/libavformat/options_table.h
@@ -42,6 +42,7 @@ static const AVOption avformat_options[] = {
 {"igndts", "ignore dts", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_IGNDTS }, INT_MIN, INT_MAX, D, "fflags"},
 {"discardcorrupt", "discard corrupted frames", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_DISCARD_CORRUPT }, INT_MIN, INT_MAX, D, "fflags"},
 {"nobuffer", "reduce the latency introduced by optional buffering", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_NOBUFFER }, 0, INT_MAX, D, "fflags"},
+{"bitexact", "do not write random/volatile data", 0, AV_OPT_TYPE_CONST, { .i64 = AVFMT_FLAG_BITEXACT }, 0, 0, E, "fflags" },
 {"analyzeduration", "how many microseconds are analyzed to estimate duration", OFFSET(max_analyze_duration), AV_OPT_TYPE_INT, {.i64 = 5*AV_TIME_BASE }, 0, INT_MAX, D},
 {"cryptokey", "decryption key", OFFSET(key), AV_OPT_TYPE_BINARY, {.dbl = 0}, 0, 0, D},
 {"indexmem", "max memory used for timestamp index (per stream)", OFFSET(max_index_size), AV_OPT_TYPE_INT, {.i64 = 1<<20 }, 0, INT_MAX, D},
diff --git a/libavformat/version.h b/libavformat/version.h
index b09d49c818..248ecdfd6c 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFORMAT_VERSION_MAJOR 55
-#define LIBAVFORMAT_VERSION_MINOR 16
+#define LIBAVFORMAT_VERSION_MINOR 17
 #define LIBAVFORMAT_VERSION_MICRO  0
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
@@ -51,5 +51,8 @@
 #ifndef FF_API_REFERENCE_DTS
 #define FF_API_REFERENCE_DTS            (LIBAVFORMAT_VERSION_MAJOR < 56)
 #endif
+#ifndef FF_API_LAVF_BITEXACT
+#define FF_API_LAVF_BITEXACT            (LIBAVFORMAT_VERSION_MAJOR < 56)
+#endif
 
 #endif /* AVFORMAT_VERSION_H */