[FFmpeg-user] Overlay one subtitle stream and copy another

[Hans Carlson]

I have an mpeg2 with 2 subtitles streams, I'd like to copy the 1st 
subtitle stream and overlay the 2nd.  When I do this, I get 
buffer underflow warnings.

If I remove the overlay filter, there are no warnings.

Am I doing something wrong?

I'd also like to take a different mpeg2 with a single subtitle stream and 
both copy AND overlay the same stream.  In this case, I'd most likely only 
overlay the forced subtitles:

   $ ffmpeg -forced_subs_only 1 -i sample.mpg ... -filter_complex '[0:v][0:2]overlay' -f vob test.mpg

I get the same kind of warnings, so I'm wondering if it's for the same 
reason.  I can provide output for that command if necessary, but it's the 
same as the command below except for the addition of "forced_subs_only" 
and "0:2" stream in the overlay filter.


$ ffmpeg -i sample.mpg -map 0:0 -map 0:1 -map 0:2 -codec:v mpeg2video -b:v 16384k -bufsize 4096k -maxrate 30000k -codec:a copy -codec:s copy -filter_complex '[0:v][0:3]overlay' -f vob test.mpg
ffmpeg version N-78949-g6f5048f Copyright (c) 2000-2016 the FFmpeg developers
   built with gcc 4.9.2 (GCC) 20150212 (Red Hat 4.9.2-6)
   configuration: --enable-gpl --enable-version3 --enable-nonfree --disable-static --enable-shared --disable-debug --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-x11grab --disable-ffplay --disable-ffserver
   libavutil      55. 19.100 / 55. 19.100
   libavcodec     57. 27.101 / 57. 27.101
   libavformat    57. 28.100 / 57. 28.100
   libavdevice    57.  0.101 / 57.  0.101
   libavfilter     6. 39.100 /  6. 39.100
   libswscale      4.  0.100 /  4.  0.100
   libswresample   2.  0.101 /  2.  0.101
   libpostproc    54.  0.100 / 54.  0.100
Input #0, mpeg, from 'sample.mpg':
   Duration: 00:00:21.98, start: 0.507000, bitrate: 6883 kb/s
     Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, smpte170m), 720x480 [SAR 32:27 DAR 16:9], Closed Captions, max. 9800 kb/s, 29.97 fps, 59.94 tbr, 90k tbn, 59.94 tbc
     Stream #0:1[0x80]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s
     Stream #0:2[0x20]: Subtitle: dvd_subtitle
     Stream #0:3[0x21]: Subtitle: dvd_subtitle
[mpeg @ 0x1e947c0] sub2video: using 720x480 canvas
Output #0, vob, to 'test.mpg':
   Metadata:
     encoder         : Lavf57.28.100
     Stream #0:0: Video: mpeg2video (Main), yuv420p, 720x480 [SAR 32:27 DAR 16:9], q=2-31, 16384 kb/s, 29.97 fps, 90k tbn, 29.97 tbc (default)
     Metadata:
       encoder         : Lavc57.27.101 mpeg2video
     Side data:
       cpb: bitrate max/min/avg: 30000000/0/16384000 buffer size: 4096000 vbv_delay: -1
     Stream #0:1: Audio: ac3, 48000 Hz, 5.1(side), 448 kb/s
     Stream #0:2: Subtitle: dvd_subtitle
Stream mapping:
   Stream #0:0 (mpeg2video) -> overlay:main
   Stream #0:3 (dvdsub) -> overlay:overlay
   overlay -> Stream #0:0 (mpeg2video)
   Stream #0:1 -> #0:1 (copy)
   Stream #0:2 -> #0:2 (copy)
Press [q] to stop, [?] for help
[Parsed_overlay_0 @ 0x1e9d020] [framesync @ 0x1f6d048] Buffer queue overflow, dropping. drop=0 speed=7.15x
     Last message repeated 27 times
[Parsed_overlay_0 @ 0x1e9d020] [framesync @ 0x1f6d048] Buffer queue overflow, dropping. drop=0 speed=8.17x
     Last message repeated 150 times
frame=  660 fps=281 q=2.0 Lsize=    5664kB time=00:00:21.98 bitrate=2110.2kbits/s dup=312 drop=0 speed=9.37x
video:4371kB audio:1202kB subtitle:5kB other streams:0kB global headers:0kB muxing overhead: 1.529098%