-frames on 2 image streams discards 1 frame

[Jérôme Martinez]

Summary of the bug:

With 2 image streams as input, " -frames" option (as well as " -frames:0 x -frames:1 x", actually " -frames:1" seems to be ignored when tested) discards 1 frame from the second (as well as third and so on) input stream.

How to reproduce:

mkdir a
ffmpeg -f lavfi -i testsrc=duration=0.080:size=16x16 a/%1d.dpx
ffmpeg -i a/%1d.dpx -i a/%1d.dpx -map 0 -map 1 -frames 2 a.mkv
ffmpeg -i a.mkv

Expected duration of 2nd stream is 2 frames (same duration as the 1st stream), the issue is visible by checking the DURATION line of each stream in the final output file.

$ mkdir a

$ ffmpeg -f lavfi -i testsrc=duration=0.080:size=16x16 a/%1d.dpx
ffmpeg version git-2019-12-15-ed9279a Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 9.2.1 (GCC) 20191125
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
  libavutil      56. 36.101 / 56. 36.101
  libavcodec     58. 65.100 / 58. 65.100
  libavformat    58. 35.101 / 58. 35.101
  libavdevice    58.  9.101 / 58.  9.101
  libavfilter     7. 68.101 /  7. 68.101
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
Input #0, lavfi, from 'testsrc=duration=0.080:size=16x16':
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: rawvideo (RGB[24] / 0x18424752), rgb24, 16x16 [SAR 1:1 DAR 1:1], 25 tbr, 25 tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> dpx (native))
Press [q] to stop, [?] for help
Output #0, image2, to 'a/%1d.dpx':
  Metadata:
    encoder         : Lavf58.35.101
    Stream #0:0: Video: dpx, rgb24, 16x16 [SAR 1:1 DAR 1:1], q=2-31, 200 kb/s, 25 fps, 25 tbn, 25 tbc
    Metadata:
      encoder         : Lavc58.65.100 dpx
[Parsed_testsrc_0 @ 00000264833ec100] EOF timestamp not reliable
frame=    2 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.08 bitrate=N/A speed=8.01x
video:5kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

$ ffmpeg -i a/%1d.dpx -i a/%1d.dpx -map 0 -map 1 -frames 2 a.mkv -y
ffmpeg version git-2019-12-15-ed9279a Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 9.2.1 (GCC) 20191125
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
  libavutil      56. 36.101 / 56. 36.101
  libavcodec     58. 65.100 / 58. 65.100
  libavformat    58. 35.101 / 58. 35.101
  libavdevice    58.  9.101 / 58.  9.101
  libavfilter     7. 68.101 /  7. 68.101
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
Input #0, image2, from 'a/%1d.dpx':
  Duration: 00:00:00.08, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: dpx, rgb24, 16x16 [SAR 1:1 DAR 1:1], 25 tbr, 25 tbn, 25 tbc
Input #1, image2, from 'a/%1d.dpx':
  Duration: 00:00:00.08, start: 0.000000, bitrate: N/A
    Stream #1:0: Video: dpx, rgb24, 16x16 [SAR 1:1 DAR 1:1], 25 tbr, 25 tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (dpx (native) -> h264 (libx264))
  Stream #1:0 -> #0:1 (dpx (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0000017d98c5c540] using SAR=1/1
[libx264 @ 0000017d98c5c540] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2 AVX512
[libx264 @ 0000017d98c5c540] profile High 4:4:4 Predictive, level 1.0, 4:4:4, 8-bit
[libx264 @ 0000017d98c5c540] 264 - core 158 - H.264/MPEG-4 AVC codec - Copyleft 2003-2019 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=4 threads=1 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
[libx264 @ 0000017d98c5e180] using SAR=1/1
[libx264 @ 0000017d98c5e180] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2 AVX512
[libx264 @ 0000017d98c5e180] profile High 4:4:4 Predictive, level 1.0, 4:4:4, 8-bit
[libx264 @ 0000017d98c5e180] 264 - core 158 - H.264/MPEG-4 AVC codec - Copyleft 2003-2019 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=4 threads=1 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, matroska, to 'a.mkv':
  Metadata:
    encoder         : Lavf58.35.101
    Stream #0:0: Video: h264 (libx264) (H264 / 0x34363248), yuv444p(progressive), 16x16 [SAR 1:1 DAR 1:1], q=-1--1, 25 fps, 1k tbn, 25 tbc
    Metadata:
      encoder         : Lavc58.65.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
    Stream #0:1: Video: h264 (libx264) (H264 / 0x34363248), yuv444p, 16x16 [SAR 1:1 DAR 1:1], q=-1--1, 25 fps, 1k tbn, 25 tbc
    Metadata:
      encoder         : Lavc58.65.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
frame=    2 fps=0.0 q=28.0 Lq=28.0 size=       3kB time=00:00:00.04 bitrate= 538.0kbits/s speed=2.05x
video:2kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 59.088287%
[libx264 @ 0000017d98c5c540] frame I:1     Avg QP:34.00  size:   198
[libx264 @ 0000017d98c5c540] frame P:1     Avg QP:36.00  size:    12
[libx264 @ 0000017d98c5c540] mb I  I16..4:  0.0%  0.0% 100.0%
[libx264 @ 0000017d98c5c540] mb P  I16..4:  0.0%  0.0%  0.0%  P16..4:  0.0%  0.0%  0.0%  0.0%  0.0%    skip:100.0%
[libx264 @ 0000017d98c5c540] 8x8 transform intra:0.0%
[libx264 @ 0000017d98c5c540] coded y,u,v intra: 100.0% 100.0% 100.0% inter: 0.0% 0.0% 0.0%
[libx264 @ 0000017d98c5c540] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 38%  6% 19%  6%  0%  6%  0% 12% 12%
[libx264 @ 0000017d98c5c540] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0000017d98c5c540] kb/s:21.00
[libx264 @ 0000017d98c5e180] frame I:1     Avg QP:36.00  size:   175
[libx264 @ 0000017d98c5e180] mb I  I16..4:  0.0%  0.0% 100.0%
[libx264 @ 0000017d98c5e180] 8x8 transform intra:0.0%
[libx264 @ 0000017d98c5e180] coded y,u,v intra: 100.0% 100.0% 100.0%
[libx264 @ 0000017d98c5e180] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 38% 12% 25%  6%  0%  6%  0% 12%  0%
[libx264 @ 0000017d98c5e180] kb/s:35.00


$ ffmpeg -i a.mkv
ffmpeg version git-2019-12-15-ed9279a Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 9.2.1 (GCC) 20191125
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
  libavutil      56. 36.101 / 56. 36.101
  libavcodec     58. 65.100 / 58. 65.100
  libavformat    58. 35.101 / 58. 35.101
  libavdevice    58.  9.101 / 58.  9.101
  libavfilter     7. 68.101 /  7. 68.101
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
Input #0, matroska,webm, from 'a.mkv':
  Metadata:
    ENCODER         : Lavf58.35.101
  Duration: 00:00:00.08, bitrate: 275 kb/s
    Stream #0:0: Video: h264 (High 4:4:4 Predictive), yuv444p(progressive), 16x16 [SAR 1:1 DAR 1:1], 25 fps, 25 tbr, 1k tbn, 50 tbc (default)
    Metadata:
      ENCODER         : Lavc58.65.100 libx264
      DURATION        : 00:00:00.080000000
    Stream #0:1: Video: h264 (High 4:4:4 Predictive), yuv444p(progressive), 16x16 [SAR 1:1 DAR 1:1], 25 fps, 25 tbr, 1k tbn, 50 tbc (default)
    Metadata:
      ENCODER         : Lavc58.65.100 libx264
      DURATION        : 00:00:00.040000000
At least one output file must be specified

Patches should be submitted to the ffmpeg-devel mailing list and not this bug tracker.

[Carl Eugen Hoyos]

Replying to Zenitram:

Expected duration of 2nd stream is 2 frames

Duration in multimedia files is measured in time (seconds etc.), number of frames is another property of video files. Please elaborate what kind of issue you see.

[Jérôme Martinez]

Duration in multimedia files is measured in time (seconds etc.), number of frames is another property of video files. Please elaborate what kind of issue you see.

Expected frame count is 2 frames (same frame count as the 1st stream) as 2nd and 1st outputted streams have the same input stream.
Issue is visible by e.g checking the duration output (stream duration is frame duration time count or frames) or by checking the count of frames in the output file (check of the file directly or demux to image content).

[Gyan]

As originally implemented, reaching the frames limit on any stream closes that file output for all its streams. So the file will end up with however many frames are written at time of closing. This appears to be a design choice, likely in response to a feature request, rather than a technical requirement.