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• Using FFMPEG to add pillar bars

  10 février 2021, par Ewok BBQ

  I have transferred some film to video files from 16mm (native 4:3). The image looks great.

  


  When I scanned them, I scanned to a native 16:9. As I overscanned them, I got the entire height of the frame, which is what I want. But it also got the soundtrack and perforation. But I want to go just to the frame line on the sides as well.

  


  I can CROP the image down with FFMPEG to remove the information outside of the framing I want [-vf crop=1330:1080:00:00].
I know this will result in a non-standard aspect ratio.
This plays fine on a computer (vlc just adapts to the non-standard).

  


  But for standardized delivery, I would love to keep the native 1920x1080 pixels, but just make everything outside of the centered 1330:1080 black.

  


  Is there a way to specifically select where the pillar bars are ?

  


  I really want to re-encode the video as little as possible.

  


  In that vein, does anyone have a better tool than -vf crop as well ?

  


  thank you very very much.

  


• ffmpeg : adding a stream non-muxed stream with correct codec type tagging

  13 janvier 2021, par Hamish

  In common use, I believe ffmpeg requires inputs to be in a specified muxer format which contains one or more data streams which can be decoded with a codec supported by the demuxer associated with the format. I have a data stream (not audio or video) which is already encoded with a codec but is not muxed. How can I get this stream into the ffmpeg pipeline with the correct codec type assigned so that the muxer knows what to do with it ?

  


  I have tried streaming the data over UDP and specifying the data demuxer. With some combinations I get get it to say it's streaming, I can never get a player to connect, presumable because the output of mpegts is either null or invalid. Command line :

  


  ffmpeg -v verbose ^
-f flv -listen 1 -i rtmp://127.0.0.1:1101 ^
-f data -i udp://127.0.0.1:1300 ^
    -map 0:v -vcodec mpeg2video -map 1:d -f mpegts -mpegts_m2ts_mode 1  udp://localhost:1200


  


  Result (partial) :

  


  Input #0, flv, from 'rtmp://127.0.0.1:1101':
  Metadata:
    encoder         : Lavf58.29.100
  Duration: 00:00:00.00, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: h264 (Constrained Baseline), 1 reference frame, yuv420p(progressive, left), 5760x1080 (5760x1088), 30 fps, 30 tbr, 1k tbn, 60 tbc
    Stream #0:1: Audio: mp3, 48000 Hz, stereo, fltp, 128 kb/s
Input #1, data, from 'udp://127.0.0.1:1300':
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #1:0: Data: none
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> mpeg2video (native))
  Stream #1:0 -> #0:1 (copy)
Press [q] to stop, [?] for help
[h264 @ 00000180d48ae700] Reinit context to 5760x1088, pix_fmt: yuv420p
[graph 0 input from stream 0:0 @ 00000180d489dcc0] w:5760 h:1080 pixfmt:yuv420p tb:1/1000 fr:30/1 sar:0/1
[mpegts @ 00000180d5f64040] Cannot automatically assign PID for stream 1
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
Error initializing output stream 0:0 --
[AVIOContext @ 00000180d48b83c0] Statistics: 0 seeks, 0 writeouts
[AVIOContext @ 00000180d4882080] Statistics: 185593 bytes read, 0 seeks
[AVIOContext @ 00000180d5f469c0] Statistics: 204 bytes read, 0 seeks
Conversion failed!


  


  The codec type name is klv, which has the tag KLVA. It is only supported by the mpegts and mxf (de)muxers. I presume there must be a way of getting into the pipeline without having a valid mpegts or mxf stream in the first place otherwise we have a kind of paradox.

  


  I've tried specifying the codec on the input, but it fails validation, I guess because the data demuxer does not support it.

  


  Somehow mp4 files can be muxed from elemental streams (h264 and aac files), but I guess there must be some special case in the code to force the codec type based on the file extension.

  


  I would really love to do this from the command line with a public build but if this is absolutely not possible, I would also welcome some advice about it could be achieved from C++ code.

  


• ffmpeg lags when streaming video+audio from RPi Zero W with Logitech C920

  7 janvier 2021, par Ema

  I've been trying to setup a baby monitor with a Raspberry Pi Zero and a Logitech C920 webcam. I does work with VLC (cvlc) but it lags too much and gets worse over time.

  


  So I am playing around with ffmpeg and I am getting some better results. This is what I've done so far.

  


  First I set the webcam to output h264 1080p natively (the Pi Zero W can't afford to do any transcoding).

  


  v4l2-ctl --set-fmt-video=width=1920,height=1080,pixelformat=1


  


  Now, if I stream audio only with

  


  ffmpeg \
-f alsa \
-i hw:1,0 \
-vn \
-flags +global_header \
-acodec aac \
-ac 1 \
-ar 16000 \
-ab 16k \
-f rtp rtp://192.168.0.10:5002 > audio.sdp


  


  it works great and the lag is about 1 second (definitely acceptable).

  


  If I stream video only with

  


  ffmpeg \
-f v4l2 \
-vcodec h264 \
-i /dev/video0 \
-an \
-vcodec copy \
-pix_fmt yuv420p \
-r 30 \
-b:v 512k \
-flags +global_header \
-f rtp rtp://192.168.0.10:5000 > video.sdp


  


  same result, very little lag (for some reason the first -vcodec is necessary to force the webcam to output h264).

  


  However, when I stream both with

  


  ffmpeg \
-f v4l2 \
-vcodec h264 \
-i /dev/video0 \
-f alsa \
-i hw:1,0 \
-an \
-preset ultrafast \
-tune zerolatency \
-vcodec copy \
-pix_fmt yuv420p \
-r 30 \
-b:v 512k \
-flags +global_header \
-f rtp rtp://192.168.0.10:5000 \
-vn \
-flags +global_header \
-acodec aac \
-ac 1 \
-ar 16000 \
-ab 16k \
-f rtp rtp://192.168.0.10:5002 > both.sdp


  


  the lag ramps up to 10 seconds and audio and video are out of sync. Does anybody know why ?

  


  I've tried UDP and TCP instead of RTP but then the lag is always high, even with audio/video only.

  


  Any suggestion is much appreciated.

  


  P.S. On the client side (MacOS) I'm receiving with

  


  ffplay -protocol_whitelist file,rtp,udp -i file.sdp