[FFmpeg-devel] [PATCH] flvdec: option for dropping negative CTS frames Initial frames with negative pts can produce video/audio desynchronization when a decoder is not prepared to handle negative pts. For example: QSV transcoding from RTMP Wowza server

[felipe at astroza.cl]

From: Felipe Astroza <felipe at astroza.cl>

Signed-off-by: Felipe Astroza <felipe at astroza.cl>
---
 libavformat/flvdec.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/libavformat/flvdec.c b/libavformat/flvdec.c
index 3959a36..1556fe0 100644
--- a/libavformat/flvdec.c
+++ b/libavformat/flvdec.c
@@ -44,6 +44,7 @@
 typedef struct FLVContext {
     const AVClass *class; ///< Class for private options.
     int trust_metadata;   ///< configure streams according onMetaData
+    int drop_negative_cts;///< drop frames if cts is negative
     int wrong_dts;        ///< wrong dts due to negative cts
     uint8_t *new_extradata[FLV_STREAM_TYPE_NB];
     int new_extradata_size[FLV_STREAM_TYPE_NB];
@@ -1139,10 +1140,16 @@ retry_duration:
             int32_t cts = (avio_rb24(s->pb) + 0xff800000) ^ 0xff800000;
             pts = dts + cts;
             if (cts < 0) { // dts might be wrong
-                if (!flv->wrong_dts)
+                if (flv->drop_negative_cts) {
                     av_log(s, AV_LOG_WARNING,
-                        "Negative cts, previous timestamps might be wrong.\n");
-                flv->wrong_dts = 1;
+                            "Negative cts, frames will be dropped.\n");
+                    dts = pts = AV_NOPTS_VALUE;
+                } else {
+                    if (!flv->wrong_dts)
+                        av_log(s, AV_LOG_WARNING,
+                            "Negative cts, previous timestamps might be wrong.\n");
+                    flv->wrong_dts = 1;
+                }
             } else if (FFABS(dts - pts) > 1000*60*15) {
                 av_log(s, AV_LOG_WARNING,
                        "invalid timestamps %"PRId64" %"PRId64"\n", dts, pts);
@@ -1253,6 +1260,7 @@ static int flv_read_seek(AVFormatContext *s, int stream_index,
 #define VD AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_DECODING_PARAM
 static const AVOption options[] = {
     { "flv_metadata", "Allocate streams according to the onMetaData array", OFFSET(trust_metadata), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, VD },
+    { "flv_drop_negative_cts", "Drop frames with negative composition timestamp", OFFSET(drop_negative_cts), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, VD },
     { "missing_streams", "", OFFSET(missing_streams), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 0xFF, VD | AV_OPT_FLAG_EXPORT | AV_OPT_FLAG_READONLY },
     { NULL }
 };
-- 
2.7.4