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• Merge audio (m4s) segments into one

  20 avril 2022, par akinuri

  I recently started learning Laravel, and currently watching an online course. Online courses are fine, but I like to have local copies, so I'm trying to download/merge segmented audio from Laracasts : Laravel 8 From Scratch series.

  


  I've written some scripts (in Python) that does the following :

  


  

  1. Download the master.json

  


  2. Read master.json and download audio segments

  


  3. Merge the segments into a single file (the file is not playable yet)

  


  4. Process the audio file via ffmpeg (now it's playable, but has issues)

  


  


  I think there's a problem with the step 3 and/or 4.

  


  In step/script 3, I create a new file, and add the contents of the segments to the file in binary.

  


  Then (step/script 4), run a ffmpeg command in python : ffmpeg -i merged-file.mp4 -c copy processed-file.mp4

  


  However, the final file doesn't work/play as expected. There's a delay in the beginning, and some parts seem to be cut off/skipped.

  


  There are three possibilities :

  


  

  • Segment files are problematic (not likely ?)

  


  • I'm doing the merging wrong

  


  • I'm doing the ffmpeg processing wrong

  


  


  Can someone guide me here ?

  


  ---

  


  The issues/colored parts in the ffmpeg output are :

  


  ...
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001cfbc0de780] could not find corresponding track id 2
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001cfbc0de780] could not find corresponding trex (id 2)
...
[aac @ 000001cfbc0f0380] Number of bands (31) exceeds limit (6).
...
[mp4 @ 000001cfbc20ecc0] track 0: codec frame size is not set
...
[mp4 @ 000001cfbc20ecc0] Non-monotonous DTS in output stream 0:0; previous: 318318, current: 286286; changing to 318319. This may result in incorrect timestamps in the output file.
...


  


  Everything required for a test case is located in GitHub (akinuri/dump/m4s-segments/). Screenshot of the contents :

  


  

  


  ---

  


  Note : there are two types/formats of audio in the master.json : mp42 and dash. dash works as expected, and seem to be used in limited videos/courses. On the other hand, mp42 appears more. So I need a way to make mp42 work.

  


• Perf Script Erroneous Dwarf Stacktrace Output

  12 juin 2020, par TheAhmad

  I used the following command to sample backtraces for an ffmpeg benchmark :

  



  sudo perf record -d --call-graph dwarf,65528 -c 1000000 -e mem_load_uops_retired.l3_miss:u ffmpeg -i /media/ahmad/DATA/Videos/video.mp4 -threads 1 -vf spp out.mp4


  



  As can be seen, PEBS is not used, the stack size is set to the maximum and the sampling period is quite large. I also limited the thread count, but this is the first part of perf script --no-demangle output :

  



  ffmpeg 11750  6670.061261:    1000000 mem_load_uops_retired.l3_miss:u:                0         5080021 N/A|SNP N/A|TLB N/A|LCK N/A
        7fffeab68844 x264_pixel_avg_w16_avx2+0x4 (/usr/lib/x86_64-linux-gnu/libx264.so.152)

ffmpeg 11750  6670.274835:    1000000 mem_load_uops_retired.l3_miss:u:                0         5080021 N/A|SNP N/A|TLB N/A|LCK N/A
        7fffeab68844 x264_pixel_avg_w16_avx2+0x4 (/usr/lib/x86_64-linux-gnu/libx264.so.152)

ffmpeg 11750  6670.496159:    1000000 mem_load_uops_retired.l3_miss:u:                0         5080021 N/A|SNP N/A|TLB N/A|LCK N/A
        7fffeab8ef89 x264_pixel_sad_x4_16x16_avx2+0x49 (/usr/lib/x86_64-linux-gnu/libx264.so.152)

ffmpeg 11750  6670.852598:    1000000 mem_load_uops_retired.l3_miss:u:                0         5080021 N/A|SNP N/A|TLB N/A|LCK N/A
        7fffeaac97b3 pixel_memset+0x293 (inlined)
        7fffeaac97b3 plane_expand_border+0x293 (inlined)
        7fffeaac97b3 x264_frame_expand_border_filtered+0x293 (/usr/lib/x86_64-linux-gnu/libx264.so.152)
        7fffeab463bc x264_fdec_filter_row+0x69c (/usr/lib/x86_64-linux-gnu/libx264.so.152)
        7fffeab49523 x264_slice_write+0x1873 (/usr/lib/x86_64-linux-gnu/libx264.so.152)
        7fffeab85285 x264_stack_align+0x15 (/usr/lib/x86_64-linux-gnu/libx264.so.152)
        7fffeab45bdb x264_slices_write+0xfb (/usr/lib/x86_64-linux-gnu/libx264.so.152)
        5555561e3d87 [unknown] ([heap])

ffmpeg 11750  6671.110007:    1000000 mem_load_uops_retired.l3_miss:u:                0         5080021 N/A|SNP N/A|TLB N/A|LCK N/A
        7fffeab6cdde x264_frame_init_lowres_core_avx2+0x8e (/usr/lib/x86_64-linux-gnu/libx264.so.152)

ffmpeg 11750  6671.463562:    1000000 mem_load_uops_retired.l3_miss:u:                0         5080021 N/A|SNP N/A|TLB N/A|LCK N/A
        7fffeaabf806 x264_macroblock_load_pic_pointers+0x886 (inlined)
        7fffeaabf806 x264_macroblock_cache_load+0x886 (inlined)
        7fffeaabf806 x264_macroblock_cache_load_progressive+0x886 (/usr/lib/x86_64-linux-gnu/libx264.so.152)
        7fffeab49204 x264_slice_write+0x1554 (/usr/lib/x86_64-linux-gnu/libx264.so.152)
        7fffeab85285 x264_stack_align+0x15 (/usr/lib/x86_64-linux-gnu/libx264.so.152)
        7fffeab45bdb x264_slices_write+0xfb (/usr/lib/x86_64-linux-gnu/libx264.so.152)
                  1c [unknown] ([unknown])


  



  None of the backtraces are correct. Because none of them begin with _start or __GI___clone. I also used LBR, instead. But it has more size constraints and, therefore, not suitable. Any suggestions on how to get around the problem ?

  



  ---

  



  UPDATE :

  



  The problem happens for all events that I checked. When I used mem_load_uops_retired.l3_miss or LLC-load-misses the problem was visible from the beginning. I also checked the output with the cycles event and everything worked fine, at the beginning. But after that, the same problem was seen.

  



  Also, note that, the problem disappears when I sample only kernel mem_load_uops_retired.l3_miss events.

  


• Artifacts after HEVC 10-bit encoding using NVENC

  18 juillet 2017, par Cryman

  Recently I purchased a brand new GPU - AORUS GeForce GTX 1080 Ti. I found out that it supports HEVC 10-bit encoding, so I wanted to give that a try. Unfortunately, after encoding I noticed some artifacts, which occur in dark scenes and last one frame of the video. You can see them on these screenshots :

  

  

  I was wondering if someone could help me figure out what might be the cause of these artifacts and how I can get rid of them.

  Here is the MI of the source video :

  ID                                       : 1
  
  Format                                   : AVC
  
  Format/Info                              : Advanced Video Codec
  
  Format profile                           : High@L4.1
  
  Format settings, CABAC                   : Yes
  
  Format settings, ReFrames                : 4 frames
  
  Codec ID                                 : V_MPEG4/ISO/AVC
  
  Duration                                 : 2 h 2 min
  
  Bit rate mode                            : Variable
  
  Bit rate                                 : 29.5 Mb/s
  
  Maximum bit rate                         : 37.0 Mb/s
  
  Width                                    : 1 920 pixels
  
  Height                                   : 1 080 pixels
  
  Display aspect ratio                     : 16:9
  
  Frame rate mode                          : Constant
  
  Frame rate                               : 23.976 (24000/1001) FPS
  
  Color space                              : YUV
  
  Chroma subsampling                       : 4:2:0
  
  Bit depth                                : 8 bits
  
  Scan type                                : Progressive
  
  Bits/(Pixel*Frame)                       : 0.593
  
  Stream size                              : 25.2 GiB (66%)
  
  Language                                 : English
  
  Default                                  : Yes
  
  Forced                                   : No

  And here is the MI of the encoded video :

  ID                                       : 1
  
  Format                                   : HEVC
  
  Format/Info                              : High Efficiency Video Coding
  
  Format profile                           : Main 10@L4@Main
  
  Codec ID                                 : V_MPEGH/ISO/HEVC
  
  Duration                                 : 2 h 2 min
  
  Bit rate                                 : 3 689 kb/s
  
  Width                                    : 1 920 pixels
  
  Height                                   : 800 pixels
  
  Display aspect ratio                     : 2.40:1
  
  Frame rate mode                          : Constant
  
  Frame rate                               : 23.976 (24000/1001) FPS
  
  Standard                                 : Component
  
  Color space                              : YUV
  
  Chroma subsampling                       : 4:2:0
  
  Bit depth                                : 10 bits
  
  Bits/(Pixel*Frame)                       : 0.100
  
  Stream size                              : 3.15 GiB (95%)
  
  Default                                  : Yes
  
  Forced                                   : No
  
  Color range                              : Limited

  The command I’m using for encoding :

  ffmpeg -hide_banner -i "" -map 0:v:0 -map_chapters -1 -map_metadata -1 -vf "crop=1920:800:0:140" -vcodec hevc_nvenc -pix_fmt p010le -preset hq -profile:v main10 -rc constqp -global_quality 21 -rc-lookahead 32 -g 240 -f matroska Video_CQP21_LAF32_GOP240.mkv