[FFmpeg-trac] #8344(ffprobe:new): ffprobe does not recognize yava420p format (alpha channel) for webm

FFmpeg trac at avcodec.org
Wed Oct 30 15:59:34 EET 2019

#8344: ffprobe does not recognize yava420p format (alpha channel) for webm
             Reporter:  jhaand       |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:  ffprobe      |                  Version:
             Keywords:  alpha        |  unspecified
  channel                            |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
 Summary of the bug: ffprobe does not recognize the alpha channel. Even
 when I encode a webm file from png files with alpha channel using ffmpeg.

 How to reproduce:
 ffmpeg -i inside_the_box_%04d.png -r 30  inside_the_box.webm
 ffprobe inside_the_box.webm

 The output from ffmpeg shows:
 [libvpx-vp9 @ 0x55ecc6b67f80] v1.8.1
 Output #0, webm, to 'inside_the_box.webm':
     encoder         : Lavf58.20.100
     Stream #0:0: Video: vp9 (libvpx-vp9), yuva420p, 1080x1920, q=-1--1,
 200 kb/s, 30 fps, 1k tbn, 30 tbc
       encoder         : Lavc58.35.100 libvpx-vp9
     Side data:
       cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1

 When I check the output file, the alpha channel is not recognised. It
 recognises the stream as yuv420p and not as yuva420p.
 Input #0, matroska,webm, from 'inside_the_box.webm':
     ENCODER         : Lavf58.20.100
   Duration: 00:00:30.07, start: 0.000000, bitrate: 95 kb/s
     Stream #0:0: Video: vp9 (Profile 0), yuv420p(tv), 1080x1920, SAR 1:1
 DAR 9:16, 30 fps, 30 tbr, 1k tbn, 1k tbc (default)
       alpha_mode      : 1
       ENCODER         : Lavc58.35.100 libvpx-vp9
       DURATION        : 00:00:30.066000000

 This makes creating and displaying a video with alpha transparency hard to

 Ffplay also has the same issue.

 If I check the file using Firefox and Chrome the alpha channel is included
 in the .webm file.
 Also when playing the file using {{{mpv --vd=libvpx-vp9 --alpha=yes
 inside_the_box.webm}}} The alpha channel is shown on the display.

 Tested on Debian-testing with ffmpeg: 4.1.4-1+b3 amd64

Ticket URL: <https://trac.ffmpeg.org/ticket/8344>
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