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• How to change resolution without compromising video quality using ffmpeg ?

  20 mars 2024, par blake banker

  I'm trying to develop a simple video transcoding system.
When you upload a video,
After extracting the video and audio separately,
I want to encode them at 360, 720, and 1080p resolutions respectively and then merge them to create three final mp4 files.
At this time, I have two questions.

  


  


  1. Is there a big difference between encoding the video and audio separately in the original video file and encoding the original video file as is ? In a related book, it is said that a system is created by separating video and audio, and I am curious as to why.

     


  


  2. I want to change the resolution without compromising the original image quality. At this time, the resolution of the uploaded file can be known at the time of upload. As a test, I created files according to each resolution, and found that the image quality was damaged. If I want to change only the resolution while keeping the original image quality, I would like to know how to adjust each ffmpeg option. We plan to change it to 360, 720, and 1080p.

     


  


  


• How can I add chapters to a mp4 file using bash script and ffmpeg

  17 septembre 2023, par Rick T

  I'm trying to add chapters to an mp4 file using bash and ffmpeg. The chapters are located in a file called chapters.txt. When the bash script is run which is called add_chapters.sh it reads the chapters.txt file and creates a file called chapters.ffmetadata. The issue is that the START and END times in the file chapters.ffmetadata aren't being created correctly. How can I fix this ?

  


  


  1. I have a file called chapters.txt that has the chapters in it.

     


     00:00:00=Intro
00:02:12=What are selections
00:03:19=Booleans


     


  


  2. The bash file I run is add_chapters.sh

     


     The code in it is :

     


     #!/bin/bash

input_file="chapters.txt"
output_file="chapters.ffmetadata"

# Create the FFmetadata chapter file
echo ";FFMETADATA1" > "$output_file"

previous_seconds=0

while IFS="=" read -r timestamp chapter_name; do
    # Convert start time to seconds
    seconds=$(date -u -d "1970-01-01 $timestamp" +"%s")

    # Calculate the end time (previous chapter's start time)
    end_seconds=$previous_seconds

    # Update previous_seconds for the next iteration
    previous_seconds=$seconds

    echo "[CHAPTER]" >> "$output_file"
    echo "TIMEBASE=1/1000" >> "$output_file"
    echo "START=${end_seconds}000" >> "$output_file"
    echo "END=${seconds}000" >> "$output_file"
    echo "title=$chapter_name" >> "$output_file"
done < "$input_file"

echo "Chapter file '$output_file' created successfully."

# Run FFmpeg to add chapters to the video
ffmpeg -i input_video.mp4 -i chapters.ffmetadata -map_metadata 1 -c:v copy -c:a copy -y output_video.mp4


     


  


  3. It creates a file called chapters.ffmetadata

     


     ;FFMETADATA1
[CHAPTER]
TIMEBASE=1/1000
START=0000
END=0000
title=Intro
[CHAPTER]
TIMEBASE=1/1000
START=0000
END=132000
title=What are selections
[CHAPTER]
TIMEBASE=1/1000
START=132000
END=199000
title=Booleans
[CHAPTER]
TIMEBASE=1/1000
START=199000
END=0000
title=


     


     The START and END times aren't being calculated correctly. How can I fix this ?

     


  


  


  ---

  


  UPDATE #1

  


  I'm almost there thanks to @Freeman code / answer.

  


  The issues in the generated
chapters.ffmetadata file are just.

  


  


  1. The first START= and END= are 0000

     


  


  2. The Intro Chapter doesn't show up (most likely caused by the first START= and END= being 0000)

     


  


  3. The Chapters seem to be shifted down by one timecode line (most likely caused by the first START= and END= being 0000)

     


      ;FFMETADATA1
[CHAPTER]
TIMEBASE=1/1000
START=0000
END=0000
title=Intro
[CHAPTER]
TIMEBASE=1/1000
START=0000
END=132000
title=What are selections ?
[CHAPTER]
TIMEBASE=1/1000
START=132000
END=199000
title=Booleans
[CHAPTER]
TIMEBASE=1/1000
START=199000
END=0000
title=
[CHAPTER]
TIMEBASE=1/1000
START=0000
END=4459000
title=

     


  


  


  ---

  


  UPDATE #2

  


  Strange ; I tried the changes @Freeman suggested but an error comes up now.

  


  Chapter end time 0 before start 199000
chapters.ffmetadata : Cannot allocate memory

  


  ;FFMETADATA1
[CHAPTER]
TIMEBASE=1/1000
START=0000
END=0000
title=Intro
[CHAPTER]
TIMEBASE=1/1000
START=0000
END=132000
title=What are selections?
[CHAPTER]
TIMEBASE=1/1000
START=132000
END=199000
title=Booleans
[CHAPTER]
TIMEBASE=1/1000
START=199000
END=0000
title=
[CHAPTER]
TIMEBASE=1/1000
START=0000
END=4459000
title=


  


  ---

  


  UPDATE #3 using his awk changes

  


  ;FFMETADATA1
[CHAPTER]
TIMEBASE=1/1000
START=0000
END=0000
title=Intro
[CHAPTER]
TIMEBASE=1/1000
START=0000
END=132000
title=What are selections?
[CHAPTER]
TIMEBASE=1/1000
START=132000
END=199000
title=Booleans
[CHAPTER]
TIMEBASE=1/1000
START=199000
END=0000
title=


  


• avutil/bfin : remove dead code

  4 juillet 2023, par Zhao Zhili

  avutil/bfin : remove dead code
  The code is unused for a decade since bf6c84d7eb27b.
  Signed-off-by : Zhao Zhili <zhilizhao@tencent.com>
  

  • [DH] libavutil/bfin/bswap.h
  • [DH] libavutil/bfin/timer.h