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• JSON Python check for data

  3 mars 2017, par Georgе Stoyanov

  So I am trying to write a script which is looking into a JSON file and check if stream with index 1 exists. Right now my program doesn’t do that. Here is the program itself. I want to check if (data["streams"][1]) exists and in case it exists to print the codec, sample rate and the bitrate of all available audio streams.

  #!/usr/bin/env python
  
  import subprocess
  
  import json
  
  import os.path
  
  
  
  # Saving the file path and the name path into input_file
  
  
  
  input_file = raw_input("Please enter the input file path: ")
  
  
  
  # Loop until the user enters a valid input file
  
  
  
  while os.path.isfile(input_file) == False:
  
          print "Please try again, the specified file / path don't exist!"
  
          input_file = raw_input("Please enter the input file path again: ")
  
  
  
  # Execution of the ffprobe command to list the general statistics of the file. I have separated both scripts because the script for analyzing the frames is taking longer time.
  
  
  
  returned_data = subprocess.check_output(['ffprobe', '-v', 'quiet', '-print_format', 'json', '-show_format', '-show_streams', input_file])
  
  
  
  # Loading of the json file
  
  
  
  data = json.loads(returned_data.decode('utf-8'))
  
  t = (data["streams"][0]["avg_frame_rate"])
  
  fps = [float(x) for x in t.split('/')]
  
  
  
  # Printing of the general information about the video file
  
  
  
  print "========================== Video ============================="
  
  print
  
  print "Codec: %s" %(data["streams"][0]["codec_long_name"])
  
  print "Profile: %s" %(data["streams"][0]["profile"])
  
  print "Resolution: %d x %d" %((data["streams"][0]["width"]), (data["streams"][0]["height"]))
  
  print "Pixel Format: %s" %(data["streams"][0]["pix_fmt"])
  
  print "Bits per sample: %s" %(data["streams"][0]["bits_per_raw_sample"])
  
  print
  
  print "========================== Audio ============================="
  
  print
  
  print "Codec: %s" %(data["streams"][1]["codec_name"])
  
  print "Sample Rate: %.3f KHz" %(int(data["streams"][1]["sample_rate"])/1000)
  
  print "Bitrate: %d Kbps" %(int(data["streams"][1]["bit_rate"])/1000)

  And here is the output of the JSON file.

  {
  
      "streams": [
  
          {
  
              "index": 0,
  
              "codec_name": "mpeg4",
  
              "codec_long_name": "MPEG-4 part 2",
  
              "profile": "Simple Profile",
  
              "codec_type": "video",
  
              "codec_time_base": "1/24",
  
              "codec_tag_string": "FMP4",
  
              "codec_tag": "0x34504d46",
  
              "width": 854,
  
              "height": 480,
  
              "coded_width": 854,
  
              "coded_height": 480,
  
              "has_b_frames": 0,
  
              "sample_aspect_ratio": "1:1",
  
              "display_aspect_ratio": "427:240",
  
              "pix_fmt": "yuv420p",
  
              "level": 1,
  
              "chroma_location": "left",
  
              "refs": 1,
  
              "quarter_sample": "false",
  
              "divx_packed": "false",
  
              "r_frame_rate": "24/1",
  
              "avg_frame_rate": "24/1",
  
              "time_base": "1/24",
  
              "start_pts": 0,
  
              "start_time": "0.000000",
  
              "duration_ts": 14315,
  
              "duration": "596.458333",
  
              "bit_rate": "2500431",
  
              "nb_frames": "14315",
  
              "disposition": {
  
                  "default": 0,
  
                  "dub": 0,
  
                  "original": 0,
  
                  "comment": 0,
  
                  "lyrics": 0,
  
                  "karaoke": 0,
  
                  "forced": 0,
  
                  "hearing_impaired": 0,
  
                  "visual_impaired": 0,
  
                  "clean_effects": 0,
  
                  "attached_pic": 0,
  
                  "timed_thumbnails": 0
  
              }
  
          },
  
          {
  
              "index": 1,
  
              "codec_name": "ac3",
  
              "codec_long_name": "ATSC A/52A (AC-3)",
  
              "codec_type": "audio",
  
              "codec_time_base": "1/48000",
  
              "codec_tag_string": "[0] [0][0]",
  
              "codec_tag": "0x2000",
  
              "sample_fmt": "fltp",
  
              "sample_rate": "48000",
  
              "channels": 6,
  
              "channel_layout": "5.1(side)",
  
              "bits_per_sample": 0,
  
              "dmix_mode": "-1",

• How can this YUV420 video have uneven dimensions

  22 décembre 2020, par Xelpi

  Just trying to cement my understanding of video codecs and can't seem to find any information about this.

  


  https://www.mediafire.com/file/cbx8sciq5mie94m/arrow.webm/file contains a tiny vp9 webm. This was generated by me via ffmpeg by doing a simple gif -> webm conversion.

  


  The source gif had a 13x11 resolution. Somehow, the output video also has a 13x11 resolution. I'm trying to understand how that is possible.

  


  As far as I understand :

  


  


  1. The YUV420 pixel format would make this impossible due to the chroma subsampling factor of 2 forcing a divisibility by two requirement.

     


  


  2. VP9 itself has a minimum block size of 16x16(?) so at least that much data must be encoded(?)

     


  


  


  Consequently, it's my assumption we have either a 14x12 or 16x16 video stream encoded here that is being somehow scaled or cropped down to 13x11.

  


  The problem is I can't find any explanation as to how this is working.

  


  Here's the ffprobe output for the stream :

  


  [STREAM]
index=0
codec_name=vp9
codec_long_name=Google VP9
profile=Profile 0
codec_type=video
codec_time_base=1/60
codec_tag_string=[0][0][0][0]
codec_tag=0x0000
width=13
height=11
coded_width=13
coded_height=11
closed_captions=0
has_b_frames=0
sample_aspect_ratio=1:1
display_aspect_ratio=13:11
pix_fmt=yuv420p
level=-99
color_range=tv
color_space=unknown
color_transfer=unknown
color_primaries=unknown
chroma_location=unspecified
field_order=unknown
timecode=N/A
refs=1
id=N/A
r_frame_rate=60/1
avg_frame_rate=60/1
time_base=1/1000
start_pts=0
start_time=0.000000
duration_ts=N/A
duration=N/A
bit_rate=N/A
max_bit_rate=N/A
bits_per_raw_sample=N/A
nb_frames=N/A
nb_read_frames=N/A
nb_read_packets=N/A
DISPOSITION:default=1
DISPOSITION:dub=0
DISPOSITION:original=0
DISPOSITION:comment=0
DISPOSITION:lyrics=0
DISPOSITION:karaoke=0
DISPOSITION:forced=0
DISPOSITION:hearing_impaired=0
DISPOSITION:visual_impaired=0
DISPOSITION:clean_effects=0
DISPOSITION:attached_pic=0
DISPOSITION:timed_thumbnails=0
TAG:alpha_mode=1
TAG:ENCODER=Lavc58.91.100 libvpx-vp9
TAG:DURATION=00:00:00.600000000
[/STREAM]


  


  and for the last frame :

  


  [FRAME]
media_type=video
stream_index=0
key_frame=0
pkt_pts=583
pkt_pts_time=0.583000
pkt_dts=583
pkt_dts_time=0.583000
best_effort_timestamp=583
best_effort_timestamp_time=0.583000
pkt_duration=16
pkt_duration_time=0.016000
pkt_pos=3639
pkt_size=15
width=13
height=11
pix_fmt=yuv420p
sample_aspect_ratio=1:1
pict_type=P
coded_picture_number=0
display_picture_number=0
interlaced_frame=0
top_field_first=0
repeat_pict=0
color_range=tv
color_space=unknown
color_primaries=unknown
color_transfer=unknown
chroma_location=unspecified
[/FRAME]


  


  going off the coded_width and coded_height values (supposed to represent the "true" width/height before any scaling(?)) plus sar value of 1, as far as I can tell this is genuinely a 13x11 video stream, but that should be impossible no ?

  


  My question is, why is this a valid video file ?

  


  If I try to e.g. zscale something to an uneven resolution in YUV420 pixel format I hit the expected chroma subsampling errors.

  


• Difference between 'display_aspect_ratio' and 'sample_aspect_ratio' in ffprobe [duplicate]

  18 juin 2018, par John Allard

  This question already has an answer here :

  • ffmpeg scaling not working for video
    
    1 answer
    

  I have an issue where a video is played in the correct 16:9 aspect ratio when played through VLC or quicktime player, but when I attempt to extract individual frames with ffmpeg the frames come out as 4:3 aspect ratio.

  The ffprobe output on the video in question is as follows

  $ ffprobe -v error -select_streams v:0 -show_entries stream -of default=noprint_wrappers=1 -print_format json movie.mp4
  
  
  
  {
  
  "programs": [
  
  
  
  ],
  
  "streams": [
  
      {
  
          "index": 0,
  
          "codec_name": "h264",
  
          "codec_long_name": "H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10",
  
          "profile": "Main",
  
          "codec_type": "video",
  
          "codec_time_base": "126669/6400000",
  
          "codec_tag_string": "avc1",
  
          "codec_tag": "0x31637661",
  
          "width": 2592,
  
          "height": 1944,
  
          "coded_width": 2592,
  
          "coded_height": 1944,
  
          "has_b_frames": 0,
  
          "sample_aspect_ratio": "4:3",
  
          "display_aspect_ratio": "16:9",
  
          "pix_fmt": "yuvj420p",
  
          "level": 50,
  
          "color_range": "pc",
  
          "color_space": "bt709",
  
          "color_transfer": "bt709",
  
          "color_primaries": "bt709",
  
          "chroma_location": "left",
  
          "refs": 1,
  
          "is_avc": "true",
  
          "nal_length_size": "4",
  
          "r_frame_rate": "25/1",
  
          "avg_frame_rate": "3200000/126669",
  
          "time_base": "1/12800",
  
          "start_pts": 0,
  
          "start_time": "0.000000",
  
          "duration_ts": 126682,
  
          "duration": "9.897031",
  
          "bit_rate": "4638928",
  
          "bits_per_raw_sample": "8",
  
          "nb_frames": "250",
  
          "disposition": {
  
              "default": 1,
  
              "dub": 0,
  
              "original": 0,
  
              "comment": 0,
  
              "lyrics": 0,
  
              "karaoke": 0,
  
              "forced": 0,
  
              "hearing_impaired": 0,
  
              "visual_impaired": 0,
  
              "clean_effects": 0,
  
              "attached_pic": 0,
  
              "timed_thumbnails": 0
  
          },
  
          "tags": {
  
              "language": "und",
  
              "handler_name": "VideoHandler"
  
          }
  
      }
  
  ]
  
  }

  So it says

      "width": 2592,
  
      "height": 1944,
  
      "coded_width": 2592,
  
      "coded_height": 1944,
  
      "has_b_frames": 0,
  
      "sample_aspect_ratio": "4:3",
  
      "display_aspect_ratio": "16:9",

  which seems odd to me. The width/height are in 4:3, the sample aspect ratio is 4:3, the display is 16:9 ?

  Now, when I play this through VLC/Quicktime the video looks fine (screenshot below)

  

  but now, if I run an ffmpeg command to extract individual frames from this video, they come out in 4:3

  ffmpeg -y -hide_banner -nostats -loglevel error -i movie.mp4 -vf select='eq(n\,10)+eq(n\,20)+eq(n\,30)+eq(n\,40)',scale=-1:640 -vsync 0 /tmp/ffmpeg_image_%04d.jpg

  

  So I guess my questions are as follows :

  1. what is the relation between display aspect ratio, sample aspect ratio, and the width/height ratio ?
  2. how to I get ffmpeg to output in the correct aspect ratio ?