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• flv reencode to mp4 for iphone/ipod via ffmpeg and x264 (quality issue)

  3 octobre 2011, par zeroasterisk

  There are a lot of questions on this topic, and I've read most of them and most of the google search results I could come up with.

  When I use FFMPEG to convert a FLV to a iphone3 compatble MP4 file, it just doesn't preserver enough of the quality. Yes, I've worked the hell out of -sameq and -b and -bt settings, text just isn't readable.

  Next I tried to split the video out and process it directly, using these instructions :
  https://sites.google.com/site/linuxencoding/x264-encoding-guide

  The problem is myplayer (via ffmpeg) was not able to determine the duration of the FLV (even though the metadata was set).

  (I assume) Because of that unknown duration, when I create the MP4 file, the resulting x264 file plays through super-fast while the audio plays at the normal rate.

  user@server:/tmp# mplayer -nosound -benchmark -sws 9 -vf dsize=640:480:0,scale=0:0,expand=640:480 -vo yuv4mpeg:file=>(x264 --demuxer y4m --crf 0 --preset slow --threads auto --output output.264 - 2>x264.log) 'input.flv'
  
  MPlayer 1.0rc4-4.4.5 (C) 2000-2010 MPlayer Team
  
  mplayer: could not connect to socket
  
  mplayer: No such file or directory
  
  Failed to open LIRC support. You will not be able to use your remote control.
  
  
  
  Playing input.flv.
  
  libavformat file format detected.
  
  [flv @ 0x1202460]Estimating duration from bitrate, this may be inaccurate
  
  [lavf] stream 0: video (vp6f), -vid 0
  
  [lavf] stream 1: audio (nellymoser), -aid 0
  
  VIDEO:  [VP6F]  1680x992  0bpp  1000.000 fps   33.4 kbps ( 4.1 kbyte/s)
  
  Clip info:
  
   audiocodecid: 6
  
   audiodatarate: 86
  
   audiosamplerate: 44100
  
   audiosamplesize: 16
  
   audiosize: 6097005
  
   canSeekToEnd: true
  
   datasize: 8609138
  
   duration: 567
  
   framerate: 2
  
   hasAudio: true
  
   hasCuePoints: false
  
   hasKeyframes: true
  
   hasMetadata: true
  
   hasVideo: true
  
   height: 992
  
   lasttimestamp: 567
  
   metadatacreator: flvtool++ (Facebook, Motion project, dweatherford)
  
   stereo: false
  
   totalframes: 1043
  
   videocodecid: 4
  
   videodatarate: 33
  
   videosize: 2316256
  
   width: 1680
  
  Using (default) progressive frame mode.Opening video filter: [expand w=640 h=480]
  
  Expand: 640 x 480, -1 ; -1, osd: 0, aspect: 0.000000, round: 1
  
  Opening video filter: [scale w=0 h=0]
  
  Opening video filter: [dsize=640:480:0]
  
  ==========================================================================
  
  Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
  
  Selected video codec: [ffvp6f] vfm: ffmpeg (FFmpeg VP6 Flash)
  
  ==========================================================================
  
  Audio: no sound
  
  Starting playback...
  
  Movie-Aspect is undefined - no prescaling applied.
  
  [swscaler @ 0x7f0c738b9620]Lanczos scaler, from yuv420p to yuv420p using MMX2
  
  VO: [yuv4mpeg] 640x480 => 641x480 Planar YV12

  I have also tried specifying FPS, but no change in results

  user@server:/tmp# mplayer -nosound -fps 25-benchmark -sws 9 -vf dsize=640:480:0,scale=0:0,expand=640:480 -vo yuv4mpeg:file=>(x264 --demuxer y4m --fps 25 --crf 0 --preset slow --threads auto --output output.264 - 2>x264.log) 'input.flv'

  Can someone tell me how to either :

  1. fix my split A/V processing/timing/duration issues ?
  2. improve the
     quality of the FFMPEG conversion of FLV to iphone3 compatible
     format ?

• ffmpeg : match audio video duration post concatenation

  20 janvier 2020, par Massimo Vantaggio

  I wrote this bash to automate concatentation of videos for dash mpeg streaming infinite loop.
  Im unable to obtain same duration for audio and video, with the videos that i’m using for testing i get always 6 ms more for audio track.
  May ask help to debug it and understand how to get same duration for both audio and video track ?

  #!/bin/bash
  
  #CANCAT 0.3
  
  
  
  cd input
  
  fps=()
  
  # GET FPS OF EACH VIDEO INTO ARRAY
  
  for f in *.mp4; do
  
      _f=$(ffmpeg -i "$f" 2>&1 | sed -n "s/.*, \\(.*\\) fp.*/\\1/p")
  
      fps+=("$_f")
  
  done
  
  
  
  #GET NUMBER OF ELEMENTS IN FPS ARRAY  
  
  tLen=${#fps[@]}
  
  #CHECK FPS EQUALITY     
  
  for tLen in "${fps[@]:1}"; do
  
      if [[ $tLen != ${fps[0]} ]]; then
  
          printf "WARNING: VIDEO’S FRAME-RATE ARE NOT EQUALS, THE PROCESS CAN’T START."
  
          printf "%s\\0" "${fps[@]}" |
  
              sort -zu |
  
              xargs -0 printf " %s"
  
          printf "\\n"
  
         exit 1
  
      fi
  
  done
  
  
  
  #AUDIO ENCODING
  
  for f in *.mp4; 
  
  do
  
  NAME=$(echo "$f" | cut -d'.' -f1) 
  
  ffmpeg -y -i "$f" -c copy -video_track_timescale 90k -c:a aac -b:a 384k -ar 44100 -ac 2 -shortest -af aresample=async=1 ../buffer/${NAME}_buffer.mp4
  
  done
  
  #-af aresample=async=1000
  
  #-filter_complex " [1:0] apad "
  
  
  
  cd ..
  
  cd buffer
  
  times=()
  
  for f in *.mp4; 
  
  do 
  
  echo "file '$f'" >> list.txt;
  
  
  
  # GET DURATION OF EACH VIDEO
  
  _t=$(ffprobe -i "$f" -show_entries format=duration -v quiet -of csv="p=0")
  
  times+=("$_t")
  
  done
  
  
  
  #SUM ALL DURATIONS
  
  TOTALDURATION=$( echo "${times[@]}" | sed 's/ /+/g' | bc )
  
  DURROUND=$(echo "$TOTALDURATION" | cut -d'.' -f1)
  
  TOTDELTA="$((DURROUND%2))"
  
  TOTDUR="$(($DURROUND-$TOTDELTA))"
  
  
  
  #GET FPS
  
  FPS="$(ffmpeg -i ${f[0]} 2>&1 | sed -n "s/.*, \(.*\) fp.*/\1/p")"
  
  #ROUND FPS
  
  FPSC=$( echo "($FPS+0.5)/1" | bc )
  
  #GET GOP
  
  GOP="$((FPSC*2))"
  
  
  
  #ENCODING MASTER TRACK
  
  ffmpeg -f concat -safe 0 -y -i list.txt -loop 1 -i ../logo/logo.png -c:a copy -c:v libx264 -x264opts keyint=$GOP:min-keyint=$GOP:no-scenecut -bf 0 -r $FPSC -b:v 4800k -maxrate 9600k -bufsize 19200k -profile:v main -crf 22 -filter_complex "[0:v][1:v]overlay=main_w-overlay_w-10:10,scale=1920:1080,setsar=1" -t $TOTDUR 1080set.mp4 
  
  
  
  #EXTRACTING AUDIO FROM MASTER VIDEO TRACK
  
  ffmpeg -y -i 1080set.mp4 -c copy -vn ../output/output_audio.mp4
  
  
  
  #REMOVE AUDIO FROM MASTER VIDEO TRACK
  
  ffmpeg -y -i 1080set.mp4 -c copy -an ../output/output_1080.mp4
  
  
  
  #CLEAN BUFFER
  
  rm *.mp4
  
  rm *.txt
  
  
  
  cd .. 
  
  cd output
  
  
  
  #ENCODE 720p
  
  ffmpeg -y -i output_1080.mp4 -an -c:v libx264 -x264opts keyint=$GOP:min-keyint=$GOP:no-scenecut -bf 0 -s 1280x720 -r $FPSC -b:v 2400k -maxrate 4800k -bufsize 9600k -profile:v main -crf 22 output_720.mp4
  
  
  
  #ENCODE 360p
  
  ffmpeg -y -i output_1080.mp4 -an -c:v libx264 -x264opts keyint=$GOP:min-keyint=$GOP:no-scenecut -bf 0 -s 640x360 -r $FPSC -b:v 800k -maxrate 1600k -bufsize 3200k -profile:v main -crf 22 output_360.mp4
  
  
  
  #VALIDATOR
  
  echo 1080p ENCODING
  
  echo GOP:   $GOP 
  
  echo VIDEO FORMAT CONTAINER DURATION:   
  
  ffprobe -v error -show_entries format=duration \
  
    -of default=noprint_wrappers=1:nokey=1 output_1080.mp4
  
  echo VIDEO STREAM DURATION:
  
  ffprobe -v error -select_streams v:0 -show_entries stream=duration \
  
    -of default=noprint_wrappers=1:nokey=1 output_1080.mp4
  
  echo AUDIO FORMAT CONTAINER DURATION:   
  
  ffprobe -v error -show_entries format=duration \
  
    -of default=noprint_wrappers=1:nokey=1 output_audio.mp4
  
  
  
  echo ______________________________________________________________
  
  
  
  echo 720p ENCODING
  
  echo GOP:   $GOP 
  
  echo VIDEO FORMAT CONTAINER DURATION:   
  
  ffprobe -v error -show_entries format=duration \
  
    -of default=noprint_wrappers=1:nokey=1 output_720.mp4
  
  echo VIDEO STREAM DURATION:
  
  ffprobe -v error -select_streams v:0 -show_entries stream=duration \
  
    -of default=noprint_wrappers=1:nokey=1 output_720.mp4
  
  echo DONE
  
  exit 1

  Here the script with my videos for test and relative folders :
  https://gofile.io/?c=WPAC0Q

• Why JPEG compressing an uncompressed image differs its original (FFmpeg, NvJPEG, ...)

  22 juin 2021, par Fruchtzwerg

  I am currently struggling to understand why recompressing an uncompressed JPEG image differs its original.

  


  It's clear, that JPEG is a lossy compression, but what if the image to compress is already uncompressed, which means all sampling losses are already included ? In other words : Downsampling and DCT should be inversable at this point without loosing data.

  


  

  


  To make sure losses are not effected by the color space conversion, this step is skipped and YUV images are used.

  


  

  1. Compress YUV image to JPEG (image.yuv —> image.yuv.jpg)

  


  2. Uncompress JPEG image to YUV image (image.yuv.jpg —> image.yuv.jpg.yuv)

  


  3. Compress YUV image to JPEG (image.yuv.jpg.yuv —> image.yuv.jpg.yuv.jpg)

  


  4. Uncompress JPEG image to YUV image (image.yuv.jpg.yuv.jpg —> image.yuv.jpg.yuv.jpg.yuv)

  


  


  Step 1 includes a lossy compression, so we will not deal with this step anymore. For me, intresting is what happens afterwards :

  


  Uncompressing the JPEG image back to YUV (step 2) leads to an image which perfectly fits all sampling steps if compressed again (step 3). So the JPEG image after step 3 should (from my understanding) be exactly the same as after step 1. Also the YUV images after step 4 and step 2 should equal each other.

  


  Looking at the steps for one 8x8 block the following simplified sequence should illustrate what I am trying to descibe. Lets start with the original YUV image, which can only be decompressed loosing all decimal places :

  


  [ 1.123, 2.345, 3.456, ... ]    (YUV)
    DTC + Quantization
[ -26, -3, -6, ... ]            (Quantized frequency space)
    Inverse DTC + Quantization
[ 1, 2, 3, ... ]                (YUV)


  


  Doing this with input, which already matches all steps, which may lead to loss of data afterwards (using round numbers in my example), the decompressed image should match its original :

  


  [ 1, 2, 3, ... ]                (YUV)
    DTC + Quantization
[ -26, -3, -6, ... ]            (Quantized frequency space)
    Inverse DTC + Quantization
[ 1, 2, 3, ... ]                (YUV)


  


  There are also some sources and discussions, which are confirming my idea :

  


  

  • need help creating Jpeg Generational Degradation code

  


  • What factors cause or prevent “generational loss” when JPEGs are recompressed multiple times ?

  


  • Lossless Chroma Subampling

  


  


  So much for theory. In praxis, I've runned these steps using ffmpeg and Nvidias jpeg samples (using NvJPEGEncoder).

  


  ffmpeg :

  


  #Create YUV image
ffmpeg -y -i image.jpg -s 1920x1080 -pix_fmt yuv420p image.yuv
#YUV to JPEG
ffmpeg -y -s 1920x1080 -pix_fmt yuv420p -i image.yuv image.yuv.jpg
#JPEG TO YUV
ffmpeg -y -i image.yuv.jpg -s 1920x1080 -pix_fmt yuv420p image.yuv.jpg.yuv
#YUV to JPEG
ffmpeg -y -s 1920x1080 -pix_fmt yuv420p -i image.yuv.jpg.yuv image.yuv.jpg.yuv.jpg
#JPEG TO YUV
ffmpeg -y -i image.yuv.jpg.yuv.jpg -s 1920x1080 -pix_fmt yuv420p image.yuv.jpg.yuv.jpg.yuv
#YUV to JPEG
ffmpeg -y -s 1920x1080 -pix_fmt yuv420p -i image.yuv.jpg.yuv.jpg.yuv image.yuv.jpg.yuv.jpg.yuv.jpg


  


  Nvidia :

  


  #Create YUV image
./jpeg_decode num_files 1 image.jpg image.yuv
#YUV to JPEG
./jpeg_encode image.yuv 1920 1080 image.yuv.jpg
#JPEG TO YUV
./jpeg_decode num_files 1 image.yuv.jpg image.yuv.jpg.yuv
#YUV to JPEG
./jpeg_encode image.yuv.jpg.yuv 1920 1080 image.yuv.jpg.yuv.jpg
#JPEG TO YUV
./jpeg_decode num_files 1 image.yuv.jpg.yuv.jpg image.yuv.jpg.yuv.jpg.yuv
#YUV to JPEG
./jpeg_encode image.yuv.jpg.yuv.jpg.yuv 1920 1080 image.yuv.jpg.yuv.jpg.yuv.jpg


  


  But a comparison of the images

  


  

  • image.yuv.jpg.yuv and image.yuv.jpg.yuv.jpg.yuv

  


  • image.yuv.jpg.yuv.jpg and image.yuv.jpg.yuv.jpg.yuv.jpg

  


  


  showing differences in the files. That brings me to my question why and where the difference gets happen, since from my understanding the files should be equal.