[FFmpeg-devel] [PATCH] libavformat/mux: Fix audio_preload

[Andreas Rheinhardt]

Commit 31f9032b added the audio_preload feature; its goal is to
interleave audio earlier than the rest. Unfortunately, it has never ever
worked, because the check for whether a packet should be interleaved
before or after another packet was completely wrong: When audio_preload
vanishes, interleave_compare_dts returns 1 if the new packet should be
interleaved earlier than the packet it is compared with and that is what
the rest of the code expects. But the codepath used when audio_preload is
set does the opposite.

Also fixes potential undefined behaviour (namely signed integer
overflow).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
---
avformat.h contains the following note about audio_preload: "not all
formats support this and unpredictable things may happen if it is used
when not supported." Has this been added because of unpredictable
results caused by the buggy check? This option seems to work fine as
long as audio_preload is not in the range of max_interleave_duration.

 libavformat/mux.c     | 22 ++++++++++++++--------
 libavformat/version.h |  2 +-
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/libavformat/mux.c b/libavformat/mux.c
index 83fe1de78f..5e1ecd8485 100644
--- a/libavformat/mux.c
+++ b/libavformat/mux.c
@@ -1001,15 +1001,21 @@ static int interleave_compare_dts(AVFormatContext *s, AVPacket *next,
     AVStream *st2 = s->streams[next->stream_index];
     int comp      = av_compare_ts(next->dts, st2->time_base, pkt->dts,
                                   st->time_base);
-    if (s->audio_preload && ((st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) != (st2->codecpar->codec_type == AVMEDIA_TYPE_AUDIO))) {
-        int64_t ts = av_rescale_q(pkt ->dts, st ->time_base, AV_TIME_BASE_Q) - s->audio_preload*(st ->codecpar->codec_type == AVMEDIA_TYPE_AUDIO);
-        int64_t ts2= av_rescale_q(next->dts, st2->time_base, AV_TIME_BASE_Q) - s->audio_preload*(st2->codecpar->codec_type == AVMEDIA_TYPE_AUDIO);
-        if (ts == ts2) {
-            ts= ( pkt ->dts* st->time_base.num*AV_TIME_BASE - s->audio_preload*(int64_t)(st ->codecpar->codec_type == AVMEDIA_TYPE_AUDIO)* st->time_base.den)*st2->time_base.den
-               -( next->dts*st2->time_base.num*AV_TIME_BASE - s->audio_preload*(int64_t)(st2->codecpar->codec_type == AVMEDIA_TYPE_AUDIO)*st2->time_base.den)* st->time_base.den;
-            ts2=0;
+    if (s->audio_preload) {
+        int preload  = st ->codecpar->codec_type == AVMEDIA_TYPE_AUDIO;
+        int preload2 = st2->codecpar->codec_type == AVMEDIA_TYPE_AUDIO;
+        if (preload != preload2) {
+            preload  *= s->audio_preload;
+            preload2 *= s->audio_preload;
+            int64_t ts = av_rescale_q(pkt ->dts, st ->time_base, AV_TIME_BASE_Q) - preload;
+            int64_t ts2= av_rescale_q(next->dts, st2->time_base, AV_TIME_BASE_Q) - preload2;
+            if (ts == ts2) {
+                ts  = ((uint64_t)pkt ->dts*st ->time_base.num*AV_TIME_BASE - (uint64_t)preload *st ->time_base.den)*st2->time_base.den
+                    - ((uint64_t)next->dts*st2->time_base.num*AV_TIME_BASE - (uint64_t)preload2*st2->time_base.den)*st ->time_base.den;
+                ts2 = 0;
+            }
+            comp = (ts2 > ts) - (ts2 < ts);
         }
-        comp= (ts>ts2) - (ts<ts2);
     }
 
     if (comp == 0)
diff --git a/libavformat/version.h b/libavformat/version.h
index 52dd95f5c6..39b00f62ab 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -33,7 +33,7 @@
 // Also please add any ticket numbers that you believe might be affected here
 #define LIBAVFORMAT_VERSION_MAJOR  58
 #define LIBAVFORMAT_VERSION_MINOR  28
-#define LIBAVFORMAT_VERSION_MICRO 100
+#define LIBAVFORMAT_VERSION_MICRO 101
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \
-- 
2.21.0