Effect of framerate Filter on an Image Source

[richardgravy]

Hello,
I was trying to accomplish something in a downstream project (mpv) and was having trouble. It was suggested to me to try the a similar action against ffmpeg directly and it has the same behaviour.
I'm not sure if this is a bug or simply undocumented behaviour.

My task:-
Generate video output from horizontally panning across an image larger than the display.

Source:-
An image file (JPEG/PNG), ideally larger than 1920x1080.

Problem:-
Image files are treated as single-frame videos with a default fps of 25. Applying a filter such as "crop=1920:1200:[st\(0,479\)\;ld\(0\)-abs\(mod\(n,2*ld\(0\)\)-ld\(0\)\)]:0" results in a single frame of output.

Solution:-
Duplicate the frame for the required duration.

Whilst trying to find the solution, I inserted the framerate filter ahead of the crop, as the filters documentation indicated that it could duplicate frames (if the new rate is higher).

Upon trying this, I found that the duration became unbounded; the filter produces infinite frames.

I was able to reproduce this without involving the crop filter, as simply as the following:-

ffmpeg -i ​http://trac.ffmpeg.org/ffmpeg-logo.png -vf framerate -map 0:v -f null -

If this is "expected", is there an easy way to limit the filter's output? I know about the "-t" argument, but that is specific to the ffmpeg frontend.

Log Output (from Fedora 31 packaged version):-
ffmpeg version 4.2.3 Copyright (c) 2000-2020 the FFmpeg developers

built with gcc 9 (GCC)
configuration: --prefix=/usr --bindir=/usr/bin --datadir=/usr/share/ffmpeg --docdir=/usr/share/doc/ffmpeg --incdir=/usr/include/ffmpeg --libdir=/usr/lib64 --mandir=/usr/share/man --arch=x86_64 --optflags='-O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection' --extra-ldflags='-Wl,-z,relro -Wl,--as-needed -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld ' --extra-cflags=' ' --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libvo-amrwbenc --enable-version3 --enable-bzlib --disable-crystalhd --enable-fontconfig --enable-frei0r --enable-gcrypt --enable-gnutls --enable-ladspa --enable-libaom --enable-libdav1d --enable-libass --enable-libbluray --enable-libcdio --enable-libdrm --enable-libjack --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libmp3lame --enable-nvenc --enable-openal --enable-opencl --enable-opengl --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librsvg --enable-libsrt --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libvorbis --enable-libv4l2 --enable-libvidstab --enable-libvmaf --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-libzimg --enable-libzvbi --enable-avfilter --enable-avresample --enable-postproc --enable-pthreads --disable-static --enable-shared --enable-gpl --disable-debug --disable-stripping --shlibdir=/usr/lib64 --enable-libmfx --enable-runtime-cpudetect
libavutil 56. 31.100 / 56. 31.100
libavcodec 58. 54.100 / 58. 54.100
libavformat 58. 29.100 / 58. 29.100
libavdevice 58. 8.100 / 58. 8.100
libavfilter 7. 57.100 / 7. 57.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 5.100 / 5. 5.100
libswresample 3. 5.100 / 3. 5.100
libpostproc 55. 5.100 / 55. 5.100

Splitting the commandline.
Reading option '-v' ... matched as option 'v' (set logging level) with argument '9'.
Reading option '-loglevel' ... matched as option 'loglevel' (set logging level) with argument '99'.
Reading option '-i' ... matched as input url with argument '​http://trac.ffmpeg.org/ffmpeg-logo.png'.
Reading option '-vf' ... matched as option 'vf' (set video filters) with argument 'framerate'.
Reading option '-map' ... matched as option 'map' (set input stream mapping) with argument '0:v'.
Reading option '-f' ... matched as option 'f' (force format) with argument 'null'.
Reading option '-' ... matched as output url.
Finished splitting the commandline.
Parsing a group of options: global .
Applying option v (set logging level) with argument 9.
Successfully parsed a group of options.
Parsing a group of options: input url ​http://trac.ffmpeg.org/ffmpeg-logo.png.
Successfully parsed a group of options.
Opening an input file: ​http://trac.ffmpeg.org/ffmpeg-logo.png.
[NULL @ 0x555a03ca0d00] Opening '​http://trac.ffmpeg.org/ffmpeg-logo.png' for reading
[http @ 0x555a03ca1780] Setting default whitelist 'http,https,tls,rtp,tcp,udp,crypto,httpproxy'
[tcp @ 0x555a03ca3600] Original list of addresses:
[tcp @ 0x555a03ca3600] Address 79.124.17.101 port 80
[tcp @ 0x555a03ca3600] Interleaved list of addresses:
[tcp @ 0x555a03ca3600] Address 79.124.17.101 port 80
[tcp @ 0x555a03ca3600] Starting connection attempt to 79.124.17.101 port 80
[tcp @ 0x555a03ca3600] Successfully connected to 79.124.17.101 port 80
[http @ 0x555a03ca1780] request: GET /ffmpeg-logo.png HTTP/1.1
User-Agent: Lavf/58.29.100
Accept: */*
Range: bytes=0-
Connection: close
Host: trac.ffmpeg.org
Icy-MetaData: 1

[http @ 0x555a03ca1780] header='HTTP/1.1 206 Partial Content'
[http @ 0x555a03ca1780] http_code=206
[http @ 0x555a03ca1780] header='Date: Wed, 07 Oct 2020 18:01:42 GMT'
[http @ 0x555a03ca1780] header='Server: Apache/2.4.18 (Ubuntu)'
[http @ 0x555a03ca1780] header='X-Frame-Options: SAMEORIGIN'
[http @ 0x555a03ca1780] header='Last-Modified: Sun, 24 Nov 2013 12:56:54 GMT'
[http @ 0x555a03ca1780] header='ETag: "2217-4ebebc81c9180"'
[http @ 0x555a03ca1780] header='Accept-Ranges: bytes'
[http @ 0x555a03ca1780] header='Content-Length: 8727'
[http @ 0x555a03ca1780] header='Content-Range: bytes 0-8726/8727'
[http @ 0x555a03ca1780] header='Connection: close'
[http @ 0x555a03ca1780] header='Content-Type: image/png'
[http @ 0x555a03ca1780] header=
Probing image2 score:50 size:2048
Probing png_pipe score:99 size:2048
[png_pipe @ 0x555a03ca0d00] Format png_pipe probed with size=2048 and score=99
[png_pipe @ 0x555a03ca0d00] Before avformat_find_stream_info() pos: 0 bytes read:3770 seeks:0 nb_streams:1
[png_pipe @ 0x555a03ca0d00] stream 0: start_time: -368934881474191040.000 duration: -368934881474191040.000
[png_pipe @ 0x555a03ca0d00] format: start_time: -9223372036854.775 duration: -9223372036854.775 bitrate=0 kb/s
[png_pipe @ 0x555a03ca0d00] After avformat_find_stream_info() pos: 8727 bytes read:8727 seeks:0 frames:1
Input #0, png_pipe, from '​http://trac.ffmpeg.org/ffmpeg-logo.png':

Duration: N/A, bitrate: N/A

Stream #0:0, 1, 1/25: Video: png, 1 reference frame, rgba(pc), 396x100, 0/1, 25 tbr, 25 tbn, 25 tbc

Successfully opened the file.
Parsing a group of options: output url -.
Applying option vf (set video filters) with argument framerate.
Applying option map (set input stream mapping) with argument 0:v.
Applying option f (force format) with argument null.
Successfully parsed a group of options.
Opening an output file: -.
Successfully opened the file.
detected 4 logical cores
Stream mapping:

Stream #0:0 -> #0:0 (png (native) -> wrapped_avframe (native))

Press [q] to stop, ? for help
cur_dts is invalid st:0 (0) [init:0 i_done:0 finish:0] (this is harmless if it occurs once at the start per stream)

Last message repeated 1 times

[graph 0 input from stream 0:0 @ 0x555a03cc0b00] Setting 'video_size' to value '396x100'
[graph 0 input from stream 0:0 @ 0x555a03cc0b00] Setting 'pix_fmt' to value '26'
[graph 0 input from stream 0:0 @ 0x555a03cc0b00] Setting 'time_base' to value '1/25'
[graph 0 input from stream 0:0 @ 0x555a03cc0b00] Setting 'pixel_aspect' to value '0/1'
[graph 0 input from stream 0:0 @ 0x555a03cc0b00] Setting 'sws_param' to value 'flags=2'
[graph 0 input from stream 0:0 @ 0x555a03cc0b00] Setting 'frame_rate' to value '25/1'
[graph 0 input from stream 0:0 @ 0x555a03cc0b00] w:396 h:100 pixfmt:rgba tb:1/25 fr:25/1 sar:0/1 sws_param:flags=2
[auto_scaler_0 @ 0x555a03cc3000] Setting 'flags' to value 'bicubic'
[auto_scaler_0 @ 0x555a03cc3000] w:iw h:ih flags:'bicubic' interl:0
[Parsed_framerate_0 @ 0x555a03cc0600] auto-inserting filter 'auto_scaler_0' between the filter 'graph 0 input from stream 0:0' and the filter 'Parsed_framerate_0'
[AVFilterGraph @ 0x555a03cab400] query_formats: 3 queried, 1 merged, 1 already done, 0 delayed
[auto_scaler_0 @ 0x555a03cc3000] picking yuv444p out of 20 ref:rgba alpha:1
[auto_scaler_0 @ 0x555a03cc3000] w:396 h:100 fmt:rgba sar:0/1 -> w:396 h:100 fmt:yuv444p sar:0/1 flags:0x4
[Parsed_framerate_0 @ 0x555a03cc0600] config_output()
[Parsed_framerate_0 @ 0x555a03cc0600] config_output() input time base:1/25 (0.040000)
[Parsed_framerate_0 @ 0x555a03cc0600] time base:1/25 -> 1/50 exact:1
[Parsed_framerate_0 @ 0x555a03cc0600] config_output() output time base:1/50 (0.020000) w:0 h:0
[Parsed_framerate_0 @ 0x555a03cc0600] fps -> fps:50/1 scene score:8.200000 interpolate start:15 end:240
Output #0, null, to 'pipe:':

Metadata:

encoder : Lavf58.29.100
Stream #0:0, 0, 1/50: Video: wrapped_avframe, 1 reference frame, yuv444p, 396x100, 0/1, q=2-31, 200 kb/s, 50 fps, 50 tbn, 50 tbc
Metadata:

encoder : Lavc58.54.100 wrapped_avframe

cur_dts is invalid st:0 (0) [init:1 i_done:0 finish:0] (this is harmless if it occurs once at the start per stream)

Last message repeated 1 times

frame=116611 fps=0.0 q=-0.0 size=N/A time=00:38:52.22 bitrate=N/A speed=4.66e+03x
frame=241634 fps=241633 q=-0.0 size=N/A time=01:20:32.68 bitrate=N/A speed=4.83e+03x
frame=368854 fps=245902 q=-0.0 size=N/A time=02:02:57.08 bitrate=N/A speed=4.92e+03x
frame=495932 fps=247965 q=-0.0 size=N/A time=02:45:18.64 bitrate=N/A speed=4.96e+03x
frame=623023 fps=249208 q=-0.0 size=N/A time=03:27:40.46 bitrate=N/A speed=4.98e+03x
frame=750524 fps=250173 q=-0.0 size=N/A time=04:10:10.48 bitrate=N/A speed=5e+03x
frame=878364 fps=250959 q=-0.0 size=N/A time=04:52:47.28 bitrate=N/A speed=5.02e+03x
frame=1005924 fps=251479 q=-0.0 size=N/A time=05:35:18.48 bitrate=N/A speed=5.03e+03x
frame=1031312 fps=251533 q=-0.0 Lsize=N/A time=05:43:46.24 bitrate=N/A speed=5.03e+03x
video:539827kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
Input file #0 (​http://trac.ffmpeg.org/ffmpeg-logo.png):

Input stream #0:0 (video): 1 packets read (8727 bytes); 1 frames decoded;
Total: 1 packets (8727 bytes) demuxed

Output file #0 (pipe:):

Output stream #0:0 (video): 1031312 frames encoded; 1031312 packets muxed (552783232 bytes);
Total: 1031312 packets (552783232 bytes) muxed

1 frames successfully decoded, 0 decoding errors
[AVIOContext @ 0x555a03cad280] Statistics: 8727 bytes read, 0 seeks

[Elon Musk]

Use loop video filter instead.