[FFmpeg-user] grayscale video streaming in ffmpeg

[Marc Elliott]

I have a raw video file (testvideo_1000f.raw) that I am trying to
stream in gray scale using ffmpeg and output the grayscale video to
output.swf. The command I am using to do this is:

ffmpeg/ffmpeg -qmin 2 -qmax 31 -s 320x240 -f rawvideo -flags gray
-pix_fmt:output gray -an -i testvideo_1000f.raw output.swf

However, the result from this command is a video stream that is in
gray scale but still contains some of the chrominance data. The output
from this command is pasted below:

3 [volta]/home/student/elliott> ffmpeg/ffmpeg -qmin 2 -qmax 31 -s
320x240 -f rawvideo -flags gray -pix_fmt:output gray -an -i
testvideo_1000f.raw output.swf
ffmpeg version N-41632-g2b1fc56 Copyright (c) 2000-2012 the FFmpeg developers
  built on Jul 29 2012 10:27:26 with gcc 4.1.2 20080704 (Red Hat 4.1.2-51)
  configuration:
  libavutil      51. 58.100 / 51. 58.100
  libavcodec     54. 25.100 / 54. 25.100
  libavformat    54.  6.101 / 54.  6.101
  libavdevice    54.  0.100 / 54.  0.100
  libavfilter     2. 80.100 /  2. 80.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0. 15.100 /  0. 15.100
*** CHOOSING 8
[rawvideo @ 0xdda9660] Estimating duration from bitrate, this may be inaccurate
Input #0, rawvideo, from 'testvideo_1000f.raw':
  Duration: N/A, start: 0.000000, bitrate: N/A
   Stream #0:0: Video: rawvideo (Y800 / 0x30303859), gray, 320x240, 25
tbr, 25 tbn, 25 tbc
File 'output.swf' already exists. Overwrite ? [y/N] y
w:320 h:240 pixfmt:gray tb:1/25 fr:25/1 sar:0/1 sws_param:flags=2
[ffmpeg_buffersink @ 0xddb7b40] No opaque field provided
[format @ 0xddb7d40] auto-inserting filter 'auto-inserted scaler 0'
between the filter 'Parsed_null_0' and the filter 'format'
[auto-inserted scaler 0 @ 0xddb7920] w:320 h:240 fmt:gray sar:0/1 ->
w:320 h:240 fmt:yuv420p sar:0/1 flags:0x4
*** CHOOSING 8
Output #0, swf, to 'output.swf':
  Metadata:
    encoder         : Lavf54.6.101
   Stream #0:0: Video: flv1, yuv420p, 320x240, q=2-31, 200 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo -> flv)
Press [q] to stop, [?] for help
Truncating packet of size 76800 to 1 2875kB time=00:00:40.84 bitrate=
576.7kbits/s
frame= 1500 fps=1035 q=24.8 Lsize=    4194kB time=00:01:00.00 bitrate=
572.6kbits/s
video:4166kB audio:0kB global headers:0kB muxing overhead 0.669245%

I am fairly new to FFMPEG and I am afraid I am using either the wrong
syntax or the wrong parameters in my command line. For some reason,
the format of the output is yuv420p. I have tried searching for this
answer all over but have had no luck.  I should also note that I am
trying to get a grayscale video by completely deleting the chrominance
information, not by just zeroing it out. I want to transmit only the
luminance data.  When I give the '-pix_fmt gray' parameter, I am
seeing the shortened buffer length I would expect from all of the
chrominance information being deleted but the output video still
contains some of the chrominance data.

Could anyone please help me and tell me why the output is being
formatted in yuv420p when I am giving the command for it to be in 8bit
grayscale?

Any help would be greatly appreciated. Thank you.