[FFmpeg-trac] #8820(avcodec:new): skip_frame nokey skips everything but IDR frames (H.264)

[FFmpeg]

#8820: skip_frame nokey skips everything but IDR frames (H.264)
-------------------------------------+-------------------------------------
             Reporter:               |                     Type:  defect
  skippableframe                     |
               Status:  new          |                 Priority:  minor
            Component:  avcodec      |                  Version:
                                     |  unspecified
             Keywords:  avc          |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 When using ffmpeg and ffprobe with `-skip_frame nokey` on H.264 files,
 only IDR frames are retained. Other I frames are skipped.

 This is doubly confusing because `ffprobe -show_frames` marks these (non-
 IDR) I frames with `key_frame=1`.

 Some retail Blu-ray disks are encoded with non-IDR I frames throughout.
 Some encoders seem to emit no IDR frames when configured for open GOP.

 This ticket for H.265 is similar.
 https://trac.ffmpeg.org/ticket/7227

 ffmpeg 4.3.1 built on FreeBSD, macOS.

 Run ffprobe with `-skip_frames nokey` and most key frames are skipped.
 {{{
 % ffprobe -v error -skip_frame nokey -show_frames test.mkv
 [h264 @ 0x80668b400] illegal short term buffer state detected
 [FRAME]
 media_type=video
 stream_index=0
 key_frame=1
 pkt_pts=10000
 pkt_pts_time=10.000000
 pkt_dts=9920
 pkt_dts_time=9.920000
 best_effort_timestamp=10000
 best_effort_timestamp_time=10.000000
 pkt_duration=40
 pkt_duration_time=0.040000
 pkt_pos=3318507
 pkt_size=43205
 width=720
 height=576
 pix_fmt=yuv420p
 sample_aspect_ratio=157:144
 pict_type=I
 coded_picture_number=1
 display_picture_number=0
 interlaced_frame=1
 top_field_first=1
 repeat_pict=0
 color_range=tv
 color_space=bt470bg
 color_primaries=bt470bg
 color_transfer=bt470bg
 chroma_location=left
 [/FRAME]
 [FRAME]
 media_type=video
 stream_index=0
 key_frame=1
 pkt_pts=0
 pkt_pts_time=0.000000
 pkt_dts=N/A
 pkt_dts_time=N/A
 best_effort_timestamp=0
 best_effort_timestamp_time=0.000000
 pkt_duration=40
 pkt_duration_time=0.040000
 pkt_pos=635
 pkt_size=2862
 width=720
 height=576
 pix_fmt=yuv420p
 sample_aspect_ratio=157:144
 pict_type=I
 coded_picture_number=0
 display_picture_number=0
 interlaced_frame=1
 top_field_first=1
 repeat_pict=0
 color_range=tv
 color_space=bt470bg
 color_primaries=bt470bg
 color_transfer=bt470bg
 chroma_location=left
 [/FRAME]
 }}}
 That's it, just the two frames.

 Run ffprobe without `-skip_frames nokey` and all I frames are recognized.
 {{{
 % ffprobe -v error -show_frames test.mkv | grep key_frame=1
 key_frame=1
 key_frame=1
 key_frame=1
 key_frame=1
 key_frame=1
 key_frame=1
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/8820>
FFmpeg <https://ffmpeg.org>
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