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• lavu/riscv : add optimisations

  12 septembre 2022, par Rémi Denis-Courmont

  lavu/riscv : add <intmath.h> optimisations
  This provides some micro-optimisations for signed integer clipping, and
  
  support for bit weight with the Zbb extension.
  

  • [DH] libavutil/intmath.h
  • [DH] libavutil/riscv/intmath.h

• How to extract fully synced audio with ffmpeg ?

  2 janvier 2023, par Brendan Hill

  I have an MP4 file with video and audio. I need to extract the audio stream only to an MP3 file.

  


  However it is critical for our application that the timing / synchronization of the audio file is exactly aligned with the original video, as we cross-correlate audio features based on timing.

  


  I currently use this command :

  


  ffmpeg -y 
   -v error 
   -map 0:a ./the-output-file-mp3
   -map 0:v ~/a-dummy-video-output-file.mp4
   -i ~/the-input-file.mp4
   -acodec copy 
  


  


  as I read somewhere that mapping both 0:a and 0:v would guarantee alignment & synchronization. I then discard the video file as it is not needed.

  


  However it is orders of magnitude faster to just extract the audio instead :

  


  ffmpeg -y 
   -v error 
   -map 0:a ./the-output-file-mp3
   -i ~/the-input-file.mp4
   -acodec copy 


  


  But I don't know if this guarantees alignment, because I read on this page that :

  


  If you only extract audio from a video stream, the length of the audio may be shorter than the length of the video. To make sure this doesn't happen, extract both audio AND video with the same call to ffmpeg, e.g. "ffmpeg -i vid.avi -map 0:a audio.wav -map 0:v onlyvideo.avi

  


  However perhaps I am putting too much weight on that comment. I don't care if the audio clip finishes early, but it is critical that it does not start late, or get de-synced from the original video at any point.

  


  What is the most efficient way with ffmpeg to extract the audio stream with a guarantee that it is 100% aligned in time to the video (and starts at exactly the same time) ?

  


  Will this method guarantee alignment ?

  


  ffmpeg -y 
   -v error 
   -i ~/the-input-file.mp4
   -vn
   -acodec copy 
   ~/the-output-file.mp4
   


  


• ffmpeg -f sdl works, ffmpeg -c codec -f sdl doesn't

  3 octobre 2022, par lunadir

  running on windows
  
anyone knows why this works

  


  ffmpeg -re -i "sample_itunes.mp4" -an -f sdl2 -


  


  and this doesn't

  


  ffmpeg -re -i "sample_itunes.mp4" -an -c libx264 -f sdl2 -


  


  doesn't show any window, output is

  


  ffmpeg.exe -re -i "sample_itunes.mp4" -an -c libx264 -r 1 -f sdl2 -
ffmpeg version n4.4-79-gde1132a891-20210803 Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 10-win32 (GCC) 20210408
  configuration: --prefix=/ffbuild/prefix --pkg-config-flags=--static --pkg-config=pkg-config --cross-prefix=x86_64-w64-mingw32- --arch=x86_64 --target-os=mingw32 --enable-gpl --enable-version3 --disable-debug --disable-w32threads --enable-pthreads --enable-iconv --enable-libxml2 --enable-zlib --enable-libfreetype --enable-libfribidi --enable-gmp --enable-lzma --enable-fontconfig --enable-libvorbis --enable-opencl --enable-libvmaf --enable-vulkan --disable-libxcb --disable-xlib --enable-amf --enable-libaom --enable-avisynth --enable-libdav1d --enable-libdavs2 --disable-libfdk-aac --enable-ffnvcodec --enable-cuda-llvm --enable-libglslang --enable-libgme --enable-libass --enable-libbluray --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvpx --enable-libwebp --enable-lv2 --enable-libmfx --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librav1e --enable-librubberband --enable-schannel --enable-sdl2 --enable-libsoxr --enable-libsrt --enable-libsvtav1 --enable-libtwolame --enable-libuavs3d --disable-libdrm --disable-vaapi --enable-libvidstab --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxvid --enable-libzimg --extra-cflags=-DLIBTWOLAME_STATIC --extra-cxxflags= --extra-ldflags=-pthread --extra-ldexeflags= --extra-libs=-lgomp --extra-version=20210803
  libavutil      56. 70.100 / 56. 70.100
  libavcodec     58.134.100 / 58.134.100
  libavformat    58. 76.100 / 58. 76.100
  libavdevice    58. 13.100 / 58. 13.100
  libavfilter     7.110.100 /  7.110.100
  libswscale      5.  9.100 /  5.  9.100
  libswresample   3.  9.100 /  3.  9.100
  libpostproc    55.  9.100 / 55.  9.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'sample_itunes.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    creation_time   : 2036-02-06T06:28:16.000000Z
    encoder         : HandBrake 0.10.2 2015060900
  Duration: 00:01:25.50, start: 0.000000, bitrate: 245 kb/s
  Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, smpte170m/smpte170m/bt709), 640x480 [SAR 1:1 DAR 4:3], 116 kb/s, 10 fps, 10 tbr, 90k tbn, 180k tbc (default)
    Metadata:
      creation_time   : 2036-02-06T06:28:16.000000Z
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 32000 Hz, mono, fltp, 125 kb/s (default)
    Metadata:
      creation_time   : 2036-02-06T06:28:16.000000Z
      handler_name    : Mono
      vendor_id       : [0][0][0][0]
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0000025cce1ab7c0] using SAR=1/1
[libx264 @ 0000025cce1ab7c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0000025cce1ab7c0] profile High, level 2.2, 4:2:0, 8-bit
[sdl,sdl2 @ 0000025cce769040] Only supports one rawvideo stream
Output #0, sdl,sdl2, to 'pipe:':
  Metadata:
    major_brand     : mp42
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.76.100
  Stream #0:0(und): Video: h264, yuv420p(tv, smpte170m/smpte170m/bt709, progressive), 640x480 [SAR 1:1 DAR 4:3], q=2-31, 1 fps, 1 tbn (default)
    Metadata:
      creation_time   : 2036-02-06T06:28:16.000000Z
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc58.134.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
[libx264 @ 0000025cce1ab7c0] non-strictly-monotonic PTSrate=N/A speed=   0x
    Last message repeated 3 times
[libx264 @ 0000025cce1ab7c0] non-strictly-monotonic PTSrate=N/A speed=   0x
    Last message repeated 3 times
[libx264 @ 0000025cce1ab7c0] non-strictly-monotonic PTSrate=N/A speed=   0x
    Last message repeated 4 times
[libx264 @ 0000025cce1ab7c0] non-strictly-monotonic PTSrate=N/A speed=   0x
    Last message repeated 3 times
[libx264 @ 0000025cce1ab7c0] non-strictly-monotonic PTSrate=N/A speed=   0x
    Last message repeated 4 times
[libx264 @ 0000025cce1ab7c0] non-strictly-monotonic PTSrate=N/A speed=   0x
    Last message repeated 3 times
[libx264 @ 0000025cce1ab7c0] non-strictly-monotonic PTSrate=N/A speed=   0x
debug=1
cur_dts is invalid st:0 (0) [init:1 i_done:0 finish:0] (this is harmless if it occurs once at the start per stream)
    Last message repeated 4 times
[h264 @ 0000025ccc8fd8c0] nal_unit_type: 1(Coded slice of a non-IDR picture), nal_ref_idc: 0
[libx264 @ 0000025cce1ab7c0] non-strictly-monotonic PTS
[h264 @ 0000025ccc8fd8c0] slice:1 F mb:0 B fix frame:15 poc:65622/65622 ref:1/1 qp:7 loop:1:0:0 weight:0 SPAT
cur_dts is invalid st:0 (0) [init:1 i_done:0 finish:0] (this is harmless if it occurs once at the start per stream)
    Last message repeated 8 times
...
frame=   60 fps=8.4 q=25.0 Lsize=N/A time=-00:00:00.10 bitrate=N/A speed=N/A
video:1kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
Input file #0 (sample_itunes.mp4):
  Input stream #0:0 (video): 74 packets read (22110 bytes); 61 frames decoded;
  Input stream #0:1 (audio): 1 packets read (18 bytes);
  Total: 75 packets (22128 bytes) demuxed
Output file #0 (pipe:):
  Output stream #0:0 (video): 60 frames encoded; 1 packets muxed (866 bytes);
  Total: 1 packets (866 bytes) muxed
61 frames successfully decoded, 0 decoding errors
[libx264 @ 000001d2952aa600] frame I:1     Avg QP: 7.93  size:   866
[libx264 @ 000001d2952aa600] frame P:23    Avg QP:13.48  size:   535
[libx264 @ 000001d2952aa600] frame B:36    Avg QP:10.98  size:    81
[libx264 @ 000001d2952aa600] consecutive B-frames: 16.7% 10.0%  0.0% 73.3%
[libx264 @ 000001d2952aa600] mb I  I16..4: 99.7%  0.1%  0.2%
[libx264 @ 000001d2952aa600] mb P  I16..4:  6.2%  3.1%  0.8%  P16..4:  1.4%  0.4%  0.2%  0.0%  0.0%    skip:88.1%
[libx264 @ 000001d2952aa600] mb B  I16..4:  0.2%  0.0%  0.0%  B16..8:  2.2%  0.2%  0.0%  direct: 0.1%  skip:97.2%  L0:35.9% L1:61.8% BI: 2.3%
[libx264 @ 000001d2952aa600] 8x8 transform intra:21.1% inter:48.3%
[libx264 @ 000001d2952aa600] coded y,uvDC,uvAC intra: 6.7% 1.9% 0.5% inter: 0.2% 0.1% 0.0%
[libx264 @ 000001d2952aa600] i16 v,h,dc,p: 57% 41%  2%  0%
[libx264 @ 000001d2952aa600] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 13% 34% 51%  0%  0%  0%  0%  1%  0%
[libx264 @ 000001d2952aa600] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 30% 34% 21%  2%  2%  3%  3%  3%  2%
[libx264 @ 000001d2952aa600] i8c dc,h,v,p: 84% 15%  2%  0%
[libx264 @ 000001d2952aa600] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 000001d2952aa600] ref P L0: 84.5%  3.6%  6.3%  5.5%
[libx264 @ 000001d2952aa600] ref B L0: 78.0% 21.2%  0.9%
[libx264 @ 000001d2952aa600] ref B L1: 96.8%  3.2%
[libx264 @ 000001d2952aa600] kb/s:21.46
[AVIOContext @ 000001d29529e780] Statistics: 232272 bytes read, 2 seeks
Conversion failed!