[FFmpeg-devel] [PATCH 2/2] avcodec/g723_1enc: Avoid skip_put_bits()

[Andreas Rheinhardt]

If a bit is reserved, it matters very much what value it has, because
otherwise a decoder conforming to a future version of the standard might
interpret the output file in an unintended manner. This implies that
one must not use skip_put_bits() for it (which does not give any
guarantees wrt what ends up in the output (in case of a little-endian
bitstream writer (as here) it writes a 0 bit)); given that the reference
encoder as well as the earlier code write a zero bit at this place, the
new code does, too.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
---
The earlier code here was unaffected by any of the bugs of
skip_put_bits, because this code uses a little-endian writer and
the number of bits written so far was always even, so that skipping
a single bit could be done in the buffer itself.

 libavcodec/g723_1enc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/g723_1enc.c b/libavcodec/g723_1enc.c
index 592840566e..b2ba3c2230 100644
--- a/libavcodec/g723_1enc.c
+++ b/libavcodec/g723_1enc.c
@@ -1030,7 +1030,7 @@ static int pack_bitstream(G723_1_ChannelContext *p, AVPacket *avpkt)
     put_bits(&pb, 1, p->subframe[3].grid_index);
 
     if (p->cur_rate == RATE_6300) {
-        skip_put_bits(&pb, 1); /* reserved bit */
+        put_bits(&pb, 1, 0); /* reserved bit */
 
         /* Write 13 bit combined position index */
         temp = (p->subframe[0].pulse_pos >> 16) * 810 +
-- 
2.20.1