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• How to set PTS value to .mp4 video frames without losing video quality

  27 janvier, par Goan

  I have searched for a solution to this problem for a while now, and tried many different approaches without any success.

  


  I have an .mp4 video (no audio) in 30Hz along with a text file timestamps.txt containing exact timestamps for each frame of the video. My goal is to embed the timestamps into the frames metadata without losing video quality.

  


  E.g. the current video timestamps (which is exactly 30Hz) :

  


  0.0333
0.0666
0.0999
...


  


  I aim to embed exact timestamps such as (which could yield e.g. 29.94Hz) :

  


  0.0313
0.0656
0.0975
...


  


  I first tried the ffmpeg -filter_complex and -vf without any success. Then I tried using PyAv (pyav==13.1.0) to set the timestamp frame by frame with two different approaches :

  


  Approach 1 : Using .add_stream(template=...)

  


  ...
TIMEBASE = Fraction(1, 10000)
pts_stamps = load_timestamps() # First five pts_stamps are [0,316,635,970,1290...]

# Open the input container and stream
input_container = av.open()
input_stream = input_container.streams.video[0]

# Create an output container and configure the output stream using template
output_container = av.open(, mode="w")
output_stream = output_container.add_stream(template=input_stream)

# Iterate through the frames and set the PTS
for i, frame in tqdm(enumerate(input_container.decode(video=0))):
    frame.pts = pts_stamps[i]
    frame.time_base = TIMEBASE

    for packet in output_stream.encode(frame):
        output_container.mux(packet)

# Finalize encoding and close the containers
for packet in output_stream.encode():
    output_container.mux(packet)

output_container.close()
input_container.close()


  


  However, this resulted in the error "ValueError : Cannot rebase to zero time." which seems to be a relatively common issue which I don't seem to be able to resolve. Not sure why.

  


  Approach 2 : Setting the output container settings manually

  


  ...
TIMEBASE = Fraction(1, 10000)
pts_stamps = load_timestamps() # First five pts_stamps are [0,316,635,970,1290...]

# Open the input container and stream
input_container = av.open()
input_stream = input_container.streams.video[0]

# Create an output container and configure the output stream using template
output_container = av.open(, mode="w")
output_stream = output_container.add_stream(input_stream.codec.name, rate=input_stream.average_rate)
output_stream.width = input_stream.width
output_stream.height = input_stream.height
output_stream.pix_fmt = input_stream.pix_fmt
output_stream.bit_rate = input_stream.bit_rate
output_stream.time_base = input_stream.time_base
output_stream.options = {"crf": "0"}

# Iterate through the frames and set the PTS
for i, frame in tqdm(enumerate(input_container.decode(video=0))):
    frame.pts = pts_stamps[i]
    frame.time_base = TIMEBASE

    for packet in output_stream.encode(frame):
        output_container.mux(packet)

# Finalize encoding and close the containers
for packet in output_stream.encode():
    output_container.mux(packet)

output_container.close()
input_container.close()


  


  This result in a video with correct timestamps. However, the quality is not the same. The output file is 4x smaller, and there seem to be an average pixel value different of 2.7 pixels for each frame. I.e. it seems the encoding is lossy.

  


  Any tips on how to resolve this ?

  


• What is the FFMPEG packet UDP format to unpack with Go ?

  2 décembre 2016, par ThetraNetwork

  How can you unpack UDP packets sent from ffmpeg ?

  I wrote a script to listen to UDP packets and write them into file, but the file is invalid and almost twice the size.

  This is how I send the data :

  ffmpeg -i video.mp4 -c:a aac -ar 48000 -ab 196k \
  
   -ac 2 -strict -2 -c:v libx264 -vb 500k -r 25 -s 320x240 \
  
   -ss 00.000 -f mp4 -movflags frag_keyframe+empty_moov \ udp://127.0.0.1:1936

  This is the code in Go. It should simply write the video into a new video file :

  package main
  
  
  
  import (
  
    "net"
  
    "os"
  
  )
  
  
  
  func main(){
  
    var buf []byte = make([]byte, 512)
  
    addr, _ := net.ResolveUDPAddr("udp", ":1936")
  
    conn, _ := net.ListenUDP("udp", addr)
  
    defer conn.Close()
  
  
  
    os.Create("new_video.mp4")
  
    f, _ := os.OpenFile("new_video.mp4", syscall.O_WRONLY, 0644)
  
    defer f.Close()
  
  
  
  
  
    for {
  
      n, _ := conn.Read(buf)
  
      f.Write(buf[0:n])
  
      buf = make([]byte, 512)
  
    }
  
  }

  Thanks

  Updated

  I changed the format to mp4 but the file is still invalid.

• Evolution #3119 (Nouveau) : Développer le classement des objets de SPIP par Glissé/lâché

  13 décembre 2013, par realet RealET

  Possibilité de classer des articles par drag’n drop dans l’interface privée, par exemple avec sortable ( http://jqueryui.com/sortable/ ) ou mêmes les images et documents, selon ce même principe (une démo http://blog.arnaud-k.fr/demos/jquery-drag-n-drop/ )

  Analyse¶

  Il y a déjà une balise #RANG qui calcule le numéro de titre s’il y en a un (ça affiche la partie numéro de numéro point espace titre).
  Idéalement, et pour assurer une bonne transition, il faudrait sans doute :

  1. Créer un champ rang
  2. modifier la balise rang en conséquence
  3. Enregistrer le numéro du titre dans le champ rang
  4. Et que l’opération de drag’n’drop :
     • modifie les champs rang impactés
     • et enregistre aussi le numéro point espace dans les titres pour rétro compatibilité (pouvoir débrayer ça par un define dans mes_options)
  5. Et rajouter un bouton pour supprimer le classement

  Et prévoir que dans les boucles, par rang !par date puisse fonctionner correctement si rang à NULL.

  Discussion originale : http://thread.gmane.org/gmane.comp.web.spip.devel/64769