#1175: mpeg2 (PS) writes bad bitrate/muxrate
-------------------------------------+-------------------------------------
Reporter: tracey_pooh | Type: defect
Status: new | Priority: critical
Component: avformat | Version: git-
Keywords: mpeg2 | master
header bug | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
example way to show the bug:
/tmp/f/ffmpeg/ffmpeg -y -i ANYVIDEO -target ntsc-dvd -frames 1
xxx.mpg;
hexdump -C -s10 -n3 xxx.mpg;
buggy:
0000000a 0c 4e 03
should be (was prior to nov2011):
0000000a 01 89 c3
the correct value, which is the 22 bits of the 3 bytes above, * 400
(gdb) p (0x0189c3 >> 2) * 400
$17 = 10080000
is the value that the "-muxrate" ffmpeg param defaults to unless
overridden
and is what "-target ntsc-dvd" will also set to.
so the ffmpeg param translating into the internal storage of mpegenc.c
is off by 400.
You can see the bug a little more obviously because the "put_bits()" of 22
bits
int value in current state is 24 bits 8-)
a sample fix/patch:
diff --git a/libavformat/mpegenc.c b/libavformat/mpegenc.c
index 0df0149..1e9e2ed 100644
--- a/libavformat/mpegenc.c
+++ b/libavformat/mpegenc.c
@@ -423,7 +423,10 @@ static int mpeg_mux_init(AVFormatContext *ctx)
video_bitrate += codec_rate;
}
- if (!s->mux_rate) {
+ if (s->mux_rate) {
+ s->mux_rate /= 400; // internal param is in units of 50 bytes
+ }
+ else {
/* we increase slightly the bitrate to take into account the
headers. XXX: compute it exactly */
bitrate += bitrate / 20;
--
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/1175>
FFmpeg <http://ffmpeg.org>
FFmpeg issue tracker
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