Slight audio latency when grabbing system audio from pulseaudio

[Sebastian Bartos]

Summary of the bug:

I'm doing screen-recordings in which I mix system audio from pulse and audio from an external microphone. The recording works, but the system audio has a slight delay (< 1 sec), just enough to be annoying.

The recording output shows two different warning messages:

1: [pulse @ 0x2804980] pa_stream_get_latency() failed
2:
[alsa @ 0x282d860] Thread message queue blocking; consider raising the thread_queue_size option (current value: 8)
[output stream 0:0 @ 0x2848f40] 100 buffers queued in output stream 0:0, something may be wrong.
[x11grab @ 0x283f220] Thread message queue blocking; consider raising the thread_queue_size option (current value: 8)
[pulse @ 0x2804980] Thread message queue blocking; consider raising the thread_queue_size option (current value: 8)

How to reproduce:

I'm using the following command to record the video. The first part grabs the microphone and system audio stream and mixes them together, then the video and puts it all together into a matroska file with one merged audio stream and one video stream of the desktop.

nice -10 ffmpeg \
    -f pulse -i alsa_output.pci-0000_00_1b.0.analog-stereo.monitor \
    -f alsa -i hw:1,0 \
    -filter_complex amix -async 1 \
    -f x11grab -r 30 -s hd1080 -i :0.0 \
    -map 0:a -map 2:v \
    -acodec libvorbis -ab 160k \
    -vcodec libx264 -tune stillimage -crf 12 -preset ultrafast \
    -threads 4 \
    -y \
    $1.mkv

ffmpeg version: efd3f407e50ec04eb9b90825bf8436f221e65de8
Compiled form git master today.
Configuration:
% ./configure --enable-gpl --enable-pthreads --enable-libpulse --enable-libx264 --enable-libvorbis --enable-libmp3lame --enable-libopus --extra-libs=-lasound

Full recording output:

% record-fs-dual-audio.sh test                                                                                                                  
ffmpeg version N-70373-gefd3f40 Copyright (c) 2000-2015 the FFmpeg developers                                                                   
  built with gcc 4.9.1 (Ubuntu 4.9.1-16ubuntu6)                                                                                                 
  configuration: --enable-gpl --enable-pthreads --enable-libpulse --enable-libx264 --enable-libvorbis --enable-libmp3lame --enable-libopus --extra-libs=-lasound                                                                                                                                
  libavutil      54. 19.100 / 54. 19.100                                                                                                        
  libavcodec     56. 26.100 / 56. 26.100                                                                                                        
  libavformat    56. 23.106 / 56. 23.106                                                                                                        
  libavdevice    56.  4.100 / 56.  4.100                                                                                                        
  libavfilter     5. 11.102 /  5. 11.102                                                                                                        
  libswscale      3.  1.101 /  3.  1.101                                                                                                        
  libswresample   1.  1.100 /  1.  1.100                                                                                                        
  libpostproc    53.  3.100 / 53.  3.100                                                                                                        
[pulse @ 0x25b9980] pa_stream_get_latency() failed                                                                                              
    Last message repeated 1 times
Guessed Channel Layout for  Input Stream #0.0 : stereo
Input #0, pulse, from 'alsa_output.pci-0000_00_1b.0.analog-stereo.monitor':
  Duration: N/A, start: 1425379593.636540, bitrate: 1536 kb/s
    Stream #0:0: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s
Guessed Channel Layout for  Input Stream #1.0 : stereo
Input #1, alsa, from 'hw:1,0':
  Duration: N/A, start: 1425379594.028598, bitrate: 1536 kb/s
    Stream #1:0: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s
[x11grab @ 0x25f3e60] Stream #0: not enough frames to estimate rate; consider increasing probesize
Input #2, x11grab, from ':0.0':
  Duration: N/A, bitrate: N/A
    Stream #2:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1920x1080, 30 fps, 30 tbr, 1000k tbn, 30 tbc
-async is forwarded to lavfi similarly to -af aresample=async=1:min_hard_comp=0.100000:first_pts=0.
    Last message repeated 1 times
No pixel format specified, yuv444p for H.264 encoding chosen.
Use -pix_fmt yuv420p for compatibility with outdated media players.
[libx264 @ 0x260a900] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
[libx264 @ 0x260a900] profile High 4:4:4 Predictive, level 4.0, 4:4:4 8-bit
[libx264 @ 0x260a900] 264 - core 142 r2431 a5831aa - H.264/MPEG-4 AVC codec - Copyleft 2003-2014 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 deblock=0:-3:-3 analyse=0:0 me=dia subme=0 psy=1 psy_rd=2.00:0.70 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=6 threads=4 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=250 keyint_min=25 scenecut=0 intra_refresh=0 rc=crf mbtree=0 crf=12.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=0
Output #0, matroska, to 'test.mkv':
  Metadata:
    encoder         : Lavf56.23.106
    Stream #0:0: Audio: vorbis (libvorbis) (oV[0][0] / 0x566F), 48000 Hz, stereo, fltp, 160 kb/s (default)
    Metadata:
      encoder         : Lavc56.26.100 libvorbis
    Stream #0:1: Video: h264 (libx264) (H264 / 0x34363248), yuv444p, 1920x1080, q=-1--1, 30 fps, 1k tbn, 30 tbc
    Metadata:
      encoder         : Lavc56.26.100 libx264
Stream mapping:
  Stream #0:0 (pcm_s16le) -> amix:input0 (graph 0)
  Stream #1:0 (pcm_s16le) -> amix:input1 (graph 0)
  amix (graph 0) -> Stream #0:0 (libvorbis)
  Stream #2:0 -> #0:1 (rawvideo (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[alsa @ 0x25e2800] Thread message queue blocking; consider raising the thread_queue_size option (current value: 8)
[output stream 0:0 @ 0x25fd6a0] 100 buffers queued in output stream 0:0, something may be wrong.
[x11grab @ 0x25f3e60] Thread message queue blocking; consider raising the thread_queue_size option (current value: 8)
[pulse @ 0x25b9980] Thread message queue blocking; consider raising the thread_queue_size option (current value: 8)
frame=  158 fps= 30 q=-1.0 Lsize=    2906kB time=00:00:05.26 bitrate=4520.4kbits/s    
video:2831kB audio:68kB subtitle:0kB other streams:0kB global headers:4kB muxing overhead: 0.273924%
[libx264 @ 0x260a900] frame I:1     Avg QP: 9.00  size:531756
[libx264 @ 0x260a900] frame P:157   Avg QP: 3.13  size: 15072
[libx264 @ 0x260a900] mb I  I16..4: 100.0%  0.0%  0.0%
[libx264 @ 0x260a900] mb P  I16..4:  0.5%  0.0%  0.0%  P16..4:  7.0%  0.0%  0.0%  0.0%  0.0%    skip:92.5%
[libx264 @ 0x260a900] coded y,u,v intra: 22.3% 23.4% 23.3% inter: 1.9% 1.8% 1.8%
[libx264 @ 0x260a900] i16 v,h,dc,p: 79% 19%  2%  0%
[libx264 @ 0x260a900] kb/s:4402.05
Received signal 2: terminating.

[Sebastian Bartos]

Hm, this seems to have fixed it's self. I don't get the error any more now. The difference is, that instead of a test recording using a source in the browser, I play a local player. Curious..