[FFmpeg-trac] #3137(undetermined:new): bitrate artefacts with libvpx
FFmpeg
trac at avcodec.org
Thu Nov 14 17:18:53 CET 2013
#3137: bitrate artefacts with libvpx
-------------------------------------+-------------------------------------
Reporter: ubitux | Owner:
Type: defect | Status: new
Priority: normal | Component:
Version: | undetermined
unspecified | Keywords: libvpx
Blocked By: | Blocking:
Reproduced by developer: 0 | Analyzed by developer: 0
-------------------------------------+-------------------------------------
When encoding a webm/vp8 with default settings, some weird artefacts
appear at regular intervals.
{{{
☭ ./ffmpeg -loop 1 -i tests/lena.pnm -vf 'scale=2*iw:2*ih' -t 20 -y
out.webm
ffmpeg version N-58093-g54af7ce Copyright (c) 2000-2013 the FFmpeg
developers
built on Nov 14 2013 19:11:51 with gcc 4.8.2 (GCC)
configuration: --enable-gpl --enable-libx264 --enable-libmp3lame
--enable-x11grab --enable-libvorbis --samples=/home/ux/fate-samples
--enable-libfreetype --enable-libvpx --cpu=native --cc='ccache cc'
libavutil 52. 53.100 / 52. 53.100
libavcodec 55. 43.100 / 55. 43.100
libavformat 55. 21.100 / 55. 21.100
libavdevice 55. 5.100 / 55. 5.100
libavfilter 3. 91.100 / 3. 91.100
libswscale 2. 5.101 / 2. 5.101
libswresample 0. 17.104 / 0. 17.104
libpostproc 52. 3.100 / 52. 3.100
Input #0, image2, from 'tests/lena.pnm':
Duration: 00:00:00.04, start: 0.000000, bitrate: N/A
Stream #0:0: Video: ppm, rgb24, 256x256, 25 fps, 25 tbr, 25 tbn, 25
tbc
[libvpx @ 0x181a160] v1.2.0
Output #0, webm, to 'out.webm':
Metadata:
encoder : Lavf55.21.100
Stream #0:0: Video: vp8 (libvpx), yuv420p, 512x512, q=-1--1, 200 kb/s,
1k tbn, 25 tbc
Stream mapping:
Stream #0:0 -> #0:0 (ppm -> libvpx)
Press [q] to stop, [?] for help
frame= 500 fps=149 q=0.0 Lsize= 434kB time=00:00:20.00 bitrate=
177.9kbits/s
video:431kB audio:0kB subtitle:0 global headers:0kB muxing overhead
0.898042%
}}}
Then play {{{out.webm}}}: at t=5s, t=10s and t=15s, one single frame gets
"flashy" (just like if bitrate was wrong/very-low for those frames). It's
less visible if bitrate is raised but still visible (try adding {{{-b:v
1M}}}).
It's probably some kind of rate control bug in libvpx, but maybe something
is wrong in the wrapper (I don't have time to dig this issue) so I'm
opening a ticket.
--
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/3137>
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