[FFmpeg-devel] [PATCH] fftools/ffmpeg: Improve streamcopy

[Andreas Rheinhardt]

do_streamcopy() has a packet that gets zero-initialized first, then gets
initialized via av_init_packet() after which some of its fields are
oerwritten again with the actually desired values (unless it's EOF): The
side data is copied into the packet with av_copy_packet_side_data() and
if the source packet is refcounted, the packet will get a new reference
to the source packet's data. Furthermore, the flags are copied and the
timestamp related fields are overwritten with new values.

This commit replaces this by using av_packet_ref() to both initialize
the packet as well as populate its fields with the right values (unless
it's EOF again in which case the packet will still be initialized). The
differences to the current approach are as follows:
a) There is no call to a deprecated function (av_copy_packet_side_data())
any more.
b) Several fields that weren't copied before are now copied from the source
packet to the new packet (e.g. pos). Some of them (the timestamp related
fields) may be immediately overwritten again and some don't seem to be
used at all (e.g. pos), but in return using av_packet_ref() allows to forgo
the initializations.
c) There was no check for whether copying side data fails or not. This
has been changed: Now the program is exited in this case.

Using av_packet_ref() does not lead to unnecessary copying of data,
because the source packets are already always refcounted (they originate
from av_read_frame()).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
---
After this patch there will be only call to av_copy_packet_side_data()
left: In libavformat/movenc.c.
Btw: Initializing the packet for flushing is actually unnecessary.

 fftools/ffmpeg.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
index b6ecb89893..8e408c808a 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -1995,12 +1995,13 @@ static void do_streamcopy(InputStream *ist, OutputStream *ost, const AVPacket *p
     InputFile   *f = input_files [ist->file_index];
     int64_t start_time = (of->start_time == AV_NOPTS_VALUE) ? 0 : of->start_time;
     int64_t ost_tb_start_time = av_rescale_q(start_time, AV_TIME_BASE_Q, ost->mux_timebase);
-    AVPacket opkt = { 0 };
-
-    av_init_packet(&opkt);
+    AVPacket opkt;
 
     // EOF: flush output bitstream filters.
     if (!pkt) {
+        av_init_packet(&opkt);
+        opkt.data = NULL;
+        opkt.size = 0;
         output_packet(of, &opkt, ost, 1);
         return;
     }
@@ -2039,10 +2040,11 @@ static void do_streamcopy(InputStream *ist, OutputStream *ost, const AVPacket *p
     if (ost->enc_ctx->codec_type == AVMEDIA_TYPE_VIDEO)
         ost->sync_opts++;
 
+    if (av_packet_ref(&opkt, pkt) < 0)
+        exit_program(1);
+
     if (pkt->pts != AV_NOPTS_VALUE)
         opkt.pts = av_rescale_q(pkt->pts, ist->st->time_base, ost->mux_timebase) - ost_tb_start_time;
-    else
-        opkt.pts = AV_NOPTS_VALUE;
 
     if (pkt->dts == AV_NOPTS_VALUE)
         opkt.dts = av_rescale_q(ist->dts, AV_TIME_BASE_Q, ost->mux_timebase);
@@ -2061,18 +2063,6 @@ static void do_streamcopy(InputStream *ist, OutputStream *ost, const AVPacket *p
 
     opkt.duration = av_rescale_q(pkt->duration, ist->st->time_base, ost->mux_timebase);
 
-    opkt.flags    = pkt->flags;
-
-    if (pkt->buf) {
-        opkt.buf = av_buffer_ref(pkt->buf);
-        if (!opkt.buf)
-            exit_program(1);
-    }
-    opkt.data = pkt->data;
-    opkt.size = pkt->size;
-
-    av_copy_packet_side_data(&opkt, pkt);
-
     output_packet(of, &opkt, ost, 0);
 }
 
-- 
2.20.1