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• 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.

  


• FFmpeg and QuickTime Player dimensions of video do not match [duplicate]

  31 mai 2020, par GRS

  I have a video.mp4, which I scaled using FFmpeg to get out.mp4. The new video has the following probe :

  



  {'streams': [{'index': 0,
   'codec_name': 'h264',
   'codec_long_name': 'H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10',
   'profile': 'High',
   'codec_type': 'video',
   'codec_time_base': '1/50',
   'codec_tag_string': 'avc1',
   'codec_tag': '0x31637661',
   'width': 886,
   'height': 1920,
   'coded_width': 896,
   'coded_height': 1920,
   'has_b_frames': 2,
   'sample_aspect_ratio': '5120:1329',
   'display_aspect_ratio': '16:9',
   'pix_fmt': 'yuv420p',
   'level': 40,
   'chroma_location': 'left',
   'refs': 1,
   'is_avc': 'true',
   'nal_length_size': '4',
   'r_frame_rate': '25/1',
   'avg_frame_rate': '25/1',
   'time_base': '1/12800',
   'start_pts': 0,
   'start_time': '0.000000',
   'duration_ts': 384512,
   'duration': '30.040000',
   'bit_rate': '490832',
   'bits_per_raw_sample': '8',
   'nb_frames': '751',
   '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'}}],
 'format': {'filename': 'out.mp4',
  'nb_streams': 1,
  'nb_programs': 0,
  'format_name': 'mov,mp4,m4a,3gp,3g2,mj2',
  'format_long_name': 'QuickTime / MOV',
  'start_time': '0.000000',
  'duration': '30.040000',
  'size': '1852948',
  'bit_rate': '493461',
  'probe_score': 100,
  'tags': {'major_brand': 'isom',
   'minor_version': '512',
   'compatible_brands': 'isomiso2avc1mp41',
   'encoder': 'Lavf58.20.100'}}}


  



  I am expecting my video player to say the video is 886 x 1920, however, it is 3413:1920.


  



  What could be the error ? I am using pix_frmt=yuva420p and codec=libx264 to create the video.

  



  The error is that my ascpect ratio remains 16:9, which is the original input video, when it should automatically change to 9:19. E.g. 3413 = 1920 * 16 / 9. So why isn't the ascpect ratio changed when the video is scaled ?

  


• FFMPEG crop a portrait image square with respect to the zoomed dimensions and x/y pan

  3 octobre 2022, par hugger

  I am making a photo crop component for my mobile app.

  


  If an image is selected from the image picker and it is above 4:5 ratio, using FFMPEG I need to crop this image 1:1 using the dynamic X/Y values along with the scale value from pinching (1.00 - 10).

  


  I trying to use these values with the FFMPEG crop/scale filter, but no matter what I try I cant seem to get the crop to work as expected... It is not matching up from the UI pan / zoom.

  


  My FFMPEG command looks like this, along with some other relevant variable code :

  


  let zoom = this._scale.__getValue(); //set dynamically by the user; ranges from 0.1 to 10
let translateY = this._translateX.__getValue(); //amount from left side
let translateX = this._translateY.__getValue(); // amount from top

//trying to first crop the width and height / the zoom for the zoom scaling..?
//then I am using translate X/Y to get my coordinates (not matching up)
//I tried to use translateXY * zoom to get the scaling factor but it still did not work...
//the image needs to be square, chain scale filter to make this happen after the original crop?)
FFmpegKit.execute(
  `-y -i ${this.state.mediaSource} -vf "crop=iw/${zoom}:ih/${zoom}:${translateX}:${translateY}, scale=iw:iw:0:0" -qscale 0 -frames:v 1 ${filterPathPostCrop}`
).then(async (session) => {
  const returnCode = await session.getReturnCode();
  if (ReturnCode.isSuccess(returnCode)) {
    this.setState({
      mediaSource: filterPathPostCrop,
      videoSourcePreview: `${filterPathPostCrop}?${new Date().getTime()}`,
      ffMPEGinProgress: null,
      aspectRatio: 1080 / 1080,
      videoTime: 0,
      isPlayingVideo: false,
      isCropping: false,
      filterOutputIsAlt: !this.state.filterOutputIsAlt,
      wasCropped: true,
    });
  } else if (ReturnCode.isCancel(returnCode)) {
    // CANCEL
  } else {
    // ERROR
    alert('error');
  }
});


  


  I appreciate any guidance I can get with this, I feel like I am close I just cant seem to get this calculation working...