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• FFMPEG - how to identify a bottleneck in hardware transcoding ?

  26 août 2021, par Henry

  In the provided example I was trying to transcode a 4K h264 source to a 1080p h264 output using Nvidia's Hardware acceleration.

  


  Relevant information :

  


  ffmpeg version git-2017-12-25-613f789 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 7.2.0 (GCC)
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-bzlib --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-amf --enable-cuda --enable-cuvid --enable-d3d11va --enable-nvenc --enable-dxva2 --enable-avisynth --enable-libmfx
  libavutil      56.  7.100 / 56.  7.100
  libavcodec     58.  9.100 / 58.  9.100
  libavformat    58.  3.100 / 58.  3.100
  libavdevice    58.  0.100 / 58.  0.100
  libavfilter     7.  7.100 /  7.  7.100
  libswscale      5.  0.101 /  5.  0.101
  libswresample   3.  0.101 /  3.  0.101
  libpostproc    55.  0.100 / 55.  0.100


  


  Command used :

  


  ffmpeg -c:v h264_cuvid -i "4K_input.mp4" -c:v h264_nvenc -preset slow -s 1920x1080 -c:a copy output.mkv


  


  Relevant PC Specs :

  


  GPU: (Gigabyte) GeForce GTX 1070 Ti
CPU: Intel Core i7 7700K
Memory: 8GB DDR4 2400MHz Single Channel.
SSD: Crucial CT525MX3


  


  While the Nvidia Desktop recording has absolutely no issues to record live h264 video in up to 50Mbps bitrates, this encoding at below 2600kbps was extremely slow utilizing barely 35% GPU.
I was unable to utilize 100% of the GPU on any video parameters.

  


  This is why I could use some advice concerning how to identify a (suspected) bottleneck.

  


• ffmpeg demux concat video output blinks/stuttering between joined clips

  11 juin 2024, par hieroshima

  I'm experiencing a strange issue with FFmpeg after partially joining a few MP4 clips into one output file (output.mp4). The problem is that the video between clips randomly blinks or stutters, showing frames from the previous scene in the next scene. This happens in a completely random manner.

  


  All my MP4 clips have the same FPS, TBR, and TBN values, except for the bitrate (bolded below), which varies for each clip. These clips were prepared and encoded using AWS MediaConvert to ensure they have consistent parameters.

  


  Here’s the ffprobe result for one of the clips :

  


  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661),
yuv420p(progressive), 640x360 [SAR 1:1 DAR 16:9], **84 kb/s**, 29.97 fps,
29.97 tbr, 30k tbn (default)


  


  Below is my input.txt file for concatenation :

  


  file 'clip1_360.mp4' 
outpoint 00:00:04.00
file 'clip2_360.mp4' 
outpoint 00:00:03.00
file 'clip3_360.mp4' 
outpoint 00:00:04.00


  


  The FFmpeg command I'm using to concatenate the clips is :

  


  ffmpeg -y -f concat -safe 0 -protocol_whitelist
file,http,https,tcp,tls -fflags +igndts -i input.txt -c copy output/output.mp4


  


  I use the -fflags +igndts flag because I receive warnings about non-monotonic DTS. I’m employing the concat demuxer to avoid re-encoding the video, as the time required to generate the output is crucial. This is why I have prepared and encoded all clips in advance to have consistent values.

  


  Here is screen recording from my video player to see this problem :

  


  https://youtu.be/SfWnCbMeOfw

  


  Any assistance or suggestions on how to resolve this issue would be greatly appreciated. Because I don't have any more idea what I can do with this. If you need some more details which I didn't provide, please let me know.

  


• Sequencing MIDI From A Chiptune

  28 avril 2013, par Multimedia Mike — Outlandish Brainstorms

  The feature requests for my game music appreciation website project continue to pour in. Many of them take the form of “please add player support for system XYZ and the chiptune library to go with it.” Most of these requests are A) plausible, and B) in process. I have also received recommendations for UI improvements which I take under consideration. Then there are the numerous requests to port everything from Native Client to JavaScript so that it will work everywhere, even on mobile, a notion which might take a separate post to debunk entirely.

  But here’s an interesting request about which I would like to speculate : Automatically convert a chiptune into a MIDI file. I immediately wanted to dismiss it as impossible or highly implausible. But, as is my habit, I started pondering the concept a little more carefully and decided that there’s an outside chance of getting some part of the idea to work.

  Intro to MIDI
  MIDI stands for Musical Instrument Digital Interface. It’s a standard musical interchange format and allows music instruments and computers to exchange musical information. The file interchange format bears the extension .mid and contains a sequence of numbers that translate into commands separated by time deltas. E.g. : turn key on (this note, this velocity) ; wait x ticks ; turn key off ; wait y ticks ; etc. I’m vastly oversimplifying, as usual.

  MIDI fascinated me back in the days of dialup internet and discrete sound cards (see also my write-up on the Gravis Ultrasound). Typical song-length MIDI files often ranged from a few kilobytes to a few 10s of kilobytes. They were significantly smaller than the MOD et al. family of tracker music formats mostly by virtue of the fact that MIDI files aren’t burdened by transporting digital audio samples.
  
  I know I’m missing a lot of details. I haven’t dealt much with MIDI in the past… 15 years or so (ever since computer audio became a blur of MP3 and AAC audio). But I’m led to believe it’s still relevant. The individual who requested this feature expressed an interest in being able to import the sequenced data into any of the many music programs that can interpret .mid files.

  The Pitch
  To limit the scope, let’s focus on music that comes from the 8-bit Nintendo Entertainment System or the original Game Boy. The former features 2 square wave channels, a triangle wave, a noise channel, and a limited digital channel. The latter creates music via 2 square waves, a wave channel, and a noise channel. The roles that these various channels usually play typically break down as : square waves represent the primary melody, triangle wave is used to simulate a bass line, noise channel approximates a variety of percussive sounds, and the DPCM/wave channels are fairly free-form. They can have random game sound effects or, if they are to assist in the music, are often used for more authentic percussive sounds.

  The various channels are controlled via an assortment of memory-mapped hardware registers. These registers are fed values such as frequency, volume, and duty cycle. My idea is to modify the music playback engine to track when various events occur. Whenever a channel is turned on or off, that corresponds to a MIDI key on or off event. If a channel is already playing but a new frequency is written, that would likely count as a note change, so log a key off event followed by a new key on event.

  There is the major obstacle of what specific note is represented by a channel in a particular state. The MIDI standard defines 128 different notes spanning 11 octaves. Empirically, I wonder if I could create a table which maps the assorted frequencies to different MIDI notes ?

  I think this strategy would only work with the square and triangle waves. Noise and digital channels ? I’m not prepared to tackle that challenge.

  Prior Work ?
  I have to wonder if there is any existing work in this area. I’m certain that people have wanted to do this before ; I wonder if anyone has succeeded ?

  Just like reverse engineering a binary program entails trying to obtain a higher level abstraction of a program from a very low level representation, this challenge feels like reverse engineering a piece of music as it is being performed and automatically expressing it in a higher level form.