Нужно «сжать» flv до 420px

ffmpeg -i yyy.flv -vcodec copy -acodec copy -s 420x240 xxx.flv
ffmpeg version 0.8.17-6:0.8.17-1
[flv @ 0x263ab20] invalid stream
[libspeex @ 0x26fe6e0] Missing Speex header, assuming defaults.
[flv @ 0x263ab20] Estimating duration from bitrate, this may be inaccurate

Seems stream 0 codec frame rate differs from container frame rate: 30.00 (30/1) -> 15.00 (30/2)
Input #0, flv, from 'yyy.flv':
  Duration: 01:52:48.73, start: 4736.596000, bitrate: N/A
    Stream #0.0: Video: h264 (Baseline), yuv420p, 640x480 [PAR 1:1 DAR 4:3], 15 tbr, 1k tbn, 30 tbc
    Stream #0.1: Audio: libspeex, 16000 Hz, 1 channels, s16

Output #0, flv, to 'xxx.flv':
  Metadata:
    encoder         : Lavf53.21.1
    Stream #0.0: Video: libx264, yuv420p, 640x480 [PAR 1:1 DAR 4:3], q=2-31, 1k tbn, 15 tbc
    Stream #0.1: Audio: libspeex, 16000 Hz, 1 channels
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
Press ctrl-c to stop encoding
[flv @ 0x263d3a0] Application provided invalid, non monotonically increasing dts to muxer in stream 0: 41674 >= 41674
av_interleaved_write_frame(): Invalid argument