[FFmpeg-user] Directshow capture and irregular timing of output to StdErr
Bouke / Videotoolshed
bouke at videotoolshed.com
Sat Mar 11 13:39:16 EET 2023
Trying to build a metering tool that displays (almost) RT values.
On Mac, all works fine with AVfoundation, but on Win with Directshow I have an issue:
C:\Users\Bouke>ffmpeg.exe -nostats -f dshow -ar 48000 -i audio="Line (Steinberg CI2)" -filter_complex "ebur128=peak=true" -f null -
Now, this works fine, BUT, the output to stderr is at very irregular intervals.
Output is as expected lines like:
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.199979 TARGET:-23 LUFS M:-120.7 S:-120.7 I: -70.0 LUFS LRA: 0.0 LU FTPK: -55.5 -71.0 dBFS TPK: -55.2 -69.8 dBFS
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.299979 TARGET:-23 LUFS M:-120.7 S:-120.7 I: -70.0 LUFS LRA: 0.0 LU FTPK: -56.2 -72.7 dBFS TPK: -55.2 -69.8 dBFS
Now, sometimes one line is outputted (as expected) but most of the times it’s 2 up to 4 lines at the same time.
That does not make for a pretty visual show if I parse it ‘as fast as possible’
I could buffer the output and do my display stuff for each line with my own interval / if buffer line length >= 4 or alike, but that would introduce half a second delay, and that does not compute well in my brain when I have to ride the faders…
Is there anything I can do to have FFmpeg spit out each line ‘as soon as it is available’?
(I’m starting FFmpeg from Python, listening to StdOut / StdErr.)
Below the full command, what you cannot see is the irregularity in when the lines arrive….
Thx,
Bouke
C:\Users\Bouke>ffmpeg.exe -nostats -f dshow -ar 48000 -i audio="Line (Steinberg CI2)" -filter_complex "ebur128=peak=true" -f null -
ffmpeg version 6.0-full_build-www.gyan.dev Copyright (c) 2000-2023 the FFmpeg developers
built with gcc 12.2.0 (Rev10, Built by MSYS2 project)
configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca --enable-sdl2 --enable-libaribb24 --enable-libdav1d --enable-libdavs2 --enable-libuavs3d --enable-libzvbi --enable-librav1e --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxvid --enable-libaom --enable-libjxl --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-liblensfun --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-d3d11va --enable-dxva2 --enable-libvpl --enable-libshaderc --enable-vulkan --enable-libplacebo --enable-opencl --enable-libcdio --enable-libgme --enable-libmodplug --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libshine --enable-libtheora --enable-libtwolame --enable-libvo-amrwbenc --enable-libilbc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-chromaprint
libavutil 58. 2.100 / 58. 2.100
libavcodec 60. 3.100 / 60. 3.100
libavformat 60. 3.100 / 60. 3.100
libavdevice 60. 1.100 / 60. 1.100
libavfilter 9. 3.100 / 9. 3.100
libswscale 7. 1.100 / 7. 1.100
libswresample 4. 10.100 / 4. 10.100
libpostproc 57. 1.100 / 57. 1.100
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, dshow, from 'audio=Line (Steinberg CI2)':
Duration: N/A, start: 2052080.982000, bitrate: 1536 kb/s
Stream #0:0: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s
[Parsed_ebur128_0 @ 00000191617889c0] Summary:
Integrated loudness:
I: -70.0 LUFS
Threshold: 0.0 LUFS
Loudness range:
LRA: 0.0 LU
Threshold: 0.0 LUFS
LRA low: 0.0 LUFS
LRA high: 0.0 LUFS
True peak:
Peak: -inf dBFS
Stream mapping:
Stream #0:0 (pcm_s16le) -> ebur128:default
ebur128:out0 -> Stream #0:0 (pcm_s16le)
Press [q] to stop, [?] for help
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.0999792 TARGET:-23 LUFS M:-120.7 S:-120.7 I: -70.0 LUFS LRA: 0.0 LU FTPK: -55.2 -69.8 dBFS TPK: -55.2 -69.8 dBFS
Output #0, null, to 'pipe:':
Metadata:
encoder : Lavf60.3.100
Stream #0:0: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
Metadata:
encoder : Lavc60.3.100 pcm_s16le
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.199979 TARGET:-23 LUFS M:-120.7 S:-120.7 I: -70.0 LUFS LRA: 0.0 LU FTPK: -55.5 -71.0 dBFS TPK: -55.2 -69.8 dBFS
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.299979 TARGET:-23 LUFS M:-120.7 S:-120.7 I: -70.0 LUFS LRA: 0.0 LU FTPK: -56.2 -72.7 dBFS TPK: -55.2 -69.8 dBFS
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.399979 TARGET:-23 LUFS M: -65.2 S:-120.7 I: -65.2 LUFS LRA: 0.0 LU FTPK: -56.3 -71.9 dBFS TPK: -55.2 -69.8 dBFS
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.499979 TARGET:-23 LUFS M: -65.2 S:-120.7 I: -65.2 LUFS LRA: 0.0 LU FTPK: -54.9 -72.0 dBFS TPK: -54.9 -69.8 dBFS
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.593979 TARGET:-23 LUFS M: -65.2 S:-120.7 I: -65.2 LUFS LRA: 0.0 LU FTPK: -56.3 -71.1 dBFS TPK: -54.9 -69.8 dBFS
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.693979 TARGET:-23 LUFS M: -65.2 S:-120.7 I: -65.2 LUFS LRA: 0.0 LU FTPK: -56.0 -70.3 dBFS TPK: -54.9 -69.8 dBFS
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.793979 TARGET:-23 LUFS M: -65.1 S:-120.7 I: -65.2 LUFS LRA: 0.0 LU FTPK: -56.4 -72.0 dBFS TPK: -54.9 -69.8 dBFS
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.893979 TARGET:-23 LUFS M: -65.1 S:-120.7 I: -65.2 LUFS LRA: 0.0 LU FTPK: -56.0 -72.2 dBFS TPK: -54.9 -69.8 dBFS
[Parsed_ebur128_0 @ 000001915fe77a40] t: 0.993979 TARGET:-23 LUFS M: -65.1 S:-120.7 I: -65.2 LUFS LRA: 0.0 LU FTPK: -55.7 -71.4 dBFS TPK: -54.9 -69.8 dBFS
[Parsed_ebur128_0 @ 000001915fe77a40] t: 1.09398 TARGET:-23 LUFS M: -65.2 S:-120.7 I: -65.2 LUFS LRA: 0.0 LU FTPK: -56.3 -74.1 dBFS TPK: -54.9 -69.8 dBFS
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