lavf: introduce AVFMT_TS_NEGATIVE

Most formats do not support negative timestamps, shift them to avoid
unexpected behaviour and a number of bad crashes.

CC:libav-stable@libav.org

Signed-off-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

6 files changed, 54 insertions, 5 deletions

diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index 067a7874b9..2512e36020 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -360,6 +360,11 @@ typedef struct AVProbeData {
 #define AVFMT_TS_NONSTRICT 0x20000 /**< Format does not require strictly
                                         increasing timestamps, but they must
                                         still be monotonic */
+#define AVFMT_TS_NEGATIVE  0x40000 /**< Format allows muxing negative
+                                        timestamps. If not set the timestamp
+                                        will be shifted in av_write_frame and
+                                        av_interleaved_write_frame so they
+                                        start from 0. */
 
 /**
  * @addtogroup lavf_encoding
@@ -1021,6 +1026,18 @@ typedef struct AVFormatContext {
      */
 #define RAW_PACKET_BUFFER_SIZE 2500000
     int raw_packet_buffer_remaining_size;
+
+    /**
+     * Offset to remap timestamps to be non-negative.
+     * Expressed in timebase units.
+     */
+    int64_t offset;
+
+    /**
+     * Timebase for the timestamp offset.
+     */
+    AVRational offset_timebase;
+
 } AVFormatContext;
 
 typedef struct AVPacketList {
diff --git a/libavformat/ffmenc.c b/libavformat/ffmenc.c
index 386487f1f9..91658e12dd 100644
--- a/libavformat/ffmenc.c
+++ b/libavformat/ffmenc.c
@@ -245,4 +245,5 @@ AVOutputFormat ff_ffm_muxer = {
     .write_header      = ffm_write_header,
     .write_packet      = ffm_write_packet,
     .write_trailer     = ffm_write_trailer,
+    .flags             = AVFMT_TS_NEGATIVE,
 };
diff --git a/libavformat/framecrcenc.c b/libavformat/framecrcenc.c
index de6fa2b960..fed0cca430 100644
--- a/libavformat/framecrcenc.c
+++ b/libavformat/framecrcenc.c
@@ -43,5 +43,6 @@ AVOutputFormat ff_framecrc_muxer = {
     .video_codec       = AV_CODEC_ID_RAWVIDEO,
     .write_header      = ff_framehash_write_header,
     .write_packet      = framecrc_write_packet,
-    .flags             = AVFMT_VARIABLE_FPS | AVFMT_TS_NONSTRICT,
+    .flags             = AVFMT_VARIABLE_FPS | AVFMT_TS_NONSTRICT |
+                         AVFMT_TS_NEGATIVE,
 };
diff --git a/libavformat/md5enc.c b/libavformat/md5enc.c
index 16412c9a34..92497045eb 100644
--- a/libavformat/md5enc.c
+++ b/libavformat/md5enc.c
@@ -127,6 +127,7 @@ AVOutputFormat ff_framemd5_muxer = {
     .write_header      = framemd5_write_header,
     .write_packet      = framemd5_write_packet,
     .write_trailer     = framemd5_write_trailer,
-    .flags             = AVFMT_VARIABLE_FPS | AVFMT_TS_NONSTRICT,
+    .flags             = AVFMT_VARIABLE_FPS | AVFMT_TS_NONSTRICT |
+                         AVFMT_TS_NEGATIVE,
 };
 #endif
diff --git a/libavformat/mux.c b/libavformat/mux.c
index 76b0fb4dc6..0b537b8c1f 100644
--- a/libavformat/mux.c
+++ b/libavformat/mux.c
@@ -391,6 +391,34 @@ static int compute_pkt_fields2(AVFormatContext *s, AVStream *st, AVPacket *pkt)
     return 0;
 }
 
+/*
+ * FIXME: this function should NEVER get undefined pts/dts beside when the
+ * AVFMT_NOTIMESTAMPS is set.
+ * Those additional safety checks should be dropped once the correct checks
+ * are set in the callers.
+ */
+
+static int write_packet(AVFormatContext *s, AVPacket *pkt)
+{
+    if (!(s->oformat->flags & (AVFMT_TS_NEGATIVE | AVFMT_NOTIMESTAMPS))) {
+        AVRational time_base = s->streams[pkt->stream_index]->time_base;
+        int64_t offset = 0;
+
+        if (!s->offset && pkt->dts != AV_NOPTS_VALUE && pkt->dts < 0) {
+            s->offset = -pkt->dts;
+            s->offset_timebase = time_base;
+        }
+        if (s->offset)
+            offset = av_rescale_q(s->offset, s->offset_timebase, time_base);
+
+        if (pkt->dts != AV_NOPTS_VALUE)
+            pkt->dts += offset;
+        if (pkt->pts != AV_NOPTS_VALUE)
+            pkt->pts += offset;
+    }
+    return s->oformat->write_packet(s, pkt);
+}
+
 int av_write_frame(AVFormatContext *s, AVPacket *pkt)
 {
     int ret;
@@ -406,7 +434,7 @@ int av_write_frame(AVFormatContext *s, AVPacket *pkt)
     if (ret < 0 && !(s->oformat->flags & AVFMT_NOTIMESTAMPS))
         return ret;
 
-    ret = s->oformat->write_packet(s, pkt);
+    ret = write_packet(s, pkt);
 
     if (ret >= 0)
         s->streams[pkt->stream_index]->nb_frames++;
@@ -544,7 +572,7 @@ int av_interleaved_write_frame(AVFormatContext *s, AVPacket *pkt)
         if (ret <= 0) //FIXME cleanup needed for ret<0 ?
             return ret;
 
-        ret = s->oformat->write_packet(s, &opkt);
+        ret = write_packet(s, &opkt);
         if (ret >= 0)
             s->streams[opkt.stream_index]->nb_frames++;
 
@@ -568,7 +596,7 @@ int av_write_trailer(AVFormatContext *s)
         if (!ret)
             break;
 
-        ret = s->oformat->write_packet(s, &pkt);
+        ret = write_packet(s, &pkt);
         if (ret >= 0)
             s->streams[pkt.stream_index]->nb_frames++;
 
diff --git a/libavformat/oggenc.c b/libavformat/oggenc.c
index 6212d16373..e01c365125 100644
--- a/libavformat/oggenc.c
+++ b/libavformat/oggenc.c
@@ -619,5 +619,6 @@ AVOutputFormat ff_ogg_muxer = {
     .write_header      = ogg_write_header,
     .write_packet      = ogg_write_packet,
     .write_trailer     = ogg_write_trailer,
+    .flags             = AVFMT_TS_NEGATIVE,
     .priv_class        = &ogg_muxer_class,
 };