[FFmpeg-devel] [PATCH v7 1/5] avformat/subtitles: extend ff_subtitles_queue_insert() to support empty events

[Marth64 <marth64@proxyid.net>]

If ff_subtitles_queue_insert() were to given a NULL buffer
with 0 length, it would still attempt to grow the packet
or memcpy depending on if merge option is enabled.

In this commit, consider a NULL buffer with 0 length as
an empty event and do not attempt to modify the packet.
This way, if a subtitle demuxer happens to pass an empty
cue or wants to use av_get_packet() to read bytes, there
are no unnecessary operations on the packet after it is
allocated.

Signed-off-by: Marth64 <marth64@proxyid.net>
---
 libavformat/subtitles.c | 4 ++++
 libavformat/subtitles.h | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/libavformat/subtitles.c b/libavformat/subtitles.c
index 3413763c7b..38d2ffb8a9 100644
--- a/libavformat/subtitles.c
+++ b/libavformat/subtitles.c
@@ -117,6 +117,8 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
         int old_len;
         sub = q->subs[q->nb_subs - 1];
         old_len = sub->size;
+        if (event == NULL && len == 0)
+            return sub;
         if (av_grow_packet(sub, len) < 0)
             return NULL;
         memcpy(sub->data + old_len, event, len);
@@ -140,6 +142,8 @@ AVPacket *ff_subtitles_queue_insert(FFDemuxSubtitlesQueue *q,
         subs[q->nb_subs++] = sub;
         sub->flags |= AV_PKT_FLAG_KEY;
         sub->pts = sub->dts = 0;
+        if (event == NULL && len == 0)
+            return sub;
         memcpy(sub->data, event, len);
     }
     return sub;
diff --git a/libavformat/subtitles.h b/libavformat/subtitles.h
index 88665663c5..ba162fa503 100644
--- a/libavformat/subtitles.h
+++ b/libavformat/subtitles.h
@@ -112,7 +112,7 @@ typedef struct {
 /**
  * Insert a new subtitle event.
  *
- * @param event the subtitle line, may not be zero terminated
+ * @param event the subtitle line (not zero terminated), or NULL on empty event
  * @param len   the length of the event (in strlen() sense, so without '\0')
  * @param merge set to 1 if the current event should be concatenated with the
  *              previous one instead of adding a new entry, 0 otherwise
-- 
2.34.1

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