[FFmpeg-trac] #9199(undetermined:new): While making an MKV/FLAC/ALSA screencast, FFMPEG cuts off the last 15 s of audio
FFmpeg
trac at avcodec.org
Sat Apr 24 23:22:12 EEST 2021
#9199: While making an MKV/FLAC/ALSA screencast, FFMPEG cuts off the last 15 s of
audio
-------------------------------------+-------------------------------------
Reporter: Neven Sajko | Type: defect
Status: new | Priority: normal
Component: | Version: git-
undetermined | master
Keywords: | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
Note: will attach the ffreport.log
== Summary of the bug
=== What I was trying to accomplish
This is on a Linux machine with Alsa and X11. I was making screencasts in
the MKV container with FLAC audio.
=== The problem I encountered
The MKV file that FFMPEG outputs doesn't contain the last 15 seconds of
audio. I.e., the audio is just replaced by silence after some point. I
didn't analyze the output file in any way, except playing it with ffplay.
Another interesting thing is that if I record a screencast with a duration
of just circa 5 seconds (so, the audio is just silence), ffplay just says
"nan" in the place in its output on the terminal where there is usually a
timestamp in the format SSS.CC.
=== What's the workaround
The workaround is to record for an extra 15 seconds, and then cut the
extra video at the end.
== How to reproduce
{{{
g=1920x1080
fr=4
d=$DISPLAY
audioCaptureDevice=hw:0
audioSampleFormat=pcm_s32le
audioNumChannels=2
audioRate=44100
f=/tmp/output.mkv
ffmpeg -probesize 50M -f x11grab -video_size "$g" -framerate "$fr" -i
"$d" \
-thread_queue_size 8192 -f alsa -channels "$audioNumChannels"
-sample_rate "$audioRate" \
-c:a "$audioSampleFormat" -ar "$audioRate" -i "$audioCaptureDevice"
\
-c:a flac -c:v libx264 -crf 17 "$f"
}}}
ffmpeg stdout/stderr:
{{{
ffmpeg started on 2021-04-24 at 19:56:38
Report written to "/tmp/ffreport.log"
Log level: 48
ffmpeg version N-102027-ge448a4b4ea Copyright (c) 2000-2021 the FFmpeg
developers
built with gcc 10.2.0 (GCC)
configuration: --prefix=/usr --disable-debug --disable-static --disable-
stripping --enable-amf --enable-avisynth --enable-cuda-llvm --enable-lto
--enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-
ladspa --enable-libaom --enable-libass --enable-libbluray --enable-
libdav1d --enable-libdrm --enable-libfreetype --enable-libfribidi
--enable-libgsm --enable-libiec61883 --enable-libjack --enable-libmfx
--enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb
--enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-
libpulse --enable-librav1e --enable-libsoxr --enable-libspeex --enable-
libsrt --enable-libssh --enable-libtheora --enable-libv4l2 --enable-
libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-
libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2
--enable-libxvid --enable-libzimg --enable-nvdec --enable-nvenc --enable-
shared --enable-version3
libavutil 56. 74.100 / 56. 74.100
libavcodec 58.136.101 / 58.136.101
libavformat 58. 78.100 / 58. 78.100
libavdevice 58. 14.100 / 58. 14.100
libavfilter 7.111.100 / 7.111.100
libswscale 5. 10.100 / 5. 10.100
libswresample 3. 10.100 / 3. 10.100
libpostproc 55. 10.100 / 55. 10.100
Input #0, x11grab, from ':0':
Duration: N/A, start: 1619294198.400763, bitrate: 265420 kb/s
Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1920x1080,
265420 kb/s, 4 fps, 4 tbr, 1000k tbn, 1000k tbc
Guessed Channel Layout for Input Stream #1.0 : stereo
Input #1, alsa, from 'hw:0':
Duration: N/A, start: 1619294200.086137, bitrate: 2822 kb/s
Stream #1:0: Audio: pcm_s32le, 44100 Hz, stereo, s32, 2822 kb/s
Stream mapping:
Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
Stream #1:0 -> #0:1 (pcm_s32le (native) -> flac (native))
Press [q] to stop, [?] for help
[libx264 @ 0x55b4c33b75c0] using cpu capabilities: MMX2 SSE2Fast SSSE3
SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x55b4c33b75c0] profile High 4:4:4 Predictive, level 4.0,
4:4:4, 8-bit
[libx264 @ 0x55b4c33b75c0] 264 - core 161 r3039 544c61f - H.264/MPEG-4 AVC
codec - Copyleft 2003-2021 - http://www.videolan.org/x264.html - options:
cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1
psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1
cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=4 threads=12
lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0
bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1
b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=4
scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=17.0
qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
[flac @ 0x55b4c33b9300] encoding as 24 bits-per-sample
Output #0, matroska, to '/tmp/output.mkv':
Metadata:
encoder : Lavf58.78.100
Stream #0:0: Video: h264 (H264 / 0x34363248), yuv444p(tv, progressive),
1920x1080, q=2-31, 4 fps, 1k tbn
Metadata:
encoder : Lavc58.136.101 libx264
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
Stream #0:1: Audio: flac ([172][241][0][0] / 0xF1AC), 44100 Hz, stereo,
s32 (24 bit), 128 kb/s
Metadata:
encoder : Lavc58.136.101 flac
frame= 32 fps=4.8 q=-1.0 Lsize= 266kB time=00:00:07.25 bitrate=
300.3kbits/s speed=1.09x
video:265kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: 0.416215%
[libx264 @ 0x55b4c33b75c0] frame I:2 Avg QP: 5.68 size:133587
[libx264 @ 0x55b4c33b75c0] frame P:8 Avg QP:13.19 size: 170
[libx264 @ 0x55b4c33b75c0] frame B:22 Avg QP:19.36 size: 81
[libx264 @ 0x55b4c33b75c0] consecutive B-frames: 6.2% 6.2% 0.0% 87.5%
[libx264 @ 0x55b4c33b75c0] mb I I16..4: 45.3% 39.3% 15.4%
[libx264 @ 0x55b4c33b75c0] mb P I16..4: 0.0% 0.0% 0.0% P16..4: 0.1%
0.0% 0.0% 0.0% 0.0% skip:99.9%
[libx264 @ 0x55b4c33b75c0] mb B I16..4: 0.0% 0.0% 0.0% B16..8: 0.1%
0.0% 0.0% direct: 0.0% skip:99.9% L0:36.5% L1:61.4% BI: 2.1%
[libx264 @ 0x55b4c33b75c0] 8x8 transform intra:39.3% inter:6.9%
[libx264 @ 0x55b4c33b75c0] coded y,u,v intra: 10.8% 0.6% 0.6% inter: 0.0%
0.0% 0.0%
[libx264 @ 0x55b4c33b75c0] i16 v,h,dc,p: 82% 17% 0% 0%
[libx264 @ 0x55b4c33b75c0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 89% 5% 6% 0%
0% 0% 0% 0% 0%
[libx264 @ 0x55b4c33b75c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 32% 41% 11% 1%
2% 1% 5% 1% 6%
[libx264 @ 0x55b4c33b75c0] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x55b4c33b75c0] ref P L0: 70.7% 0.0% 17.6% 11.7%
[libx264 @ 0x55b4c33b75c0] ref B L0: 71.3% 16.7% 12.0%
[libx264 @ 0x55b4c33b75c0] ref B L1: 96.7% 3.3%
[libx264 @ 0x55b4c33b75c0] kb/s:270.33
}}}
--
Ticket URL: <https://trac.ffmpeg.org/ticket/9199>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker
More information about the FFmpeg-trac
mailing list