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>

1 files changed, 17 insertions, 0 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 {