[FFmpeg-user] Trouble grabbing from TV capture device

[Simon Roberts]

I was unclear:

On Thu, Aug 27, 2020 at 2:52 PM Simon Roberts <
simon at dancingcloudservices.com> wrote:

> I have a little device that takes "old" composite video and sends it out
> to USB. It's recognized by video4linux2 and I can watch the VHS tapes that
> I'm trying to capture using xawtv simply using:
>
> v4lctl -c /dev/video2 setnorm NTSC
> v4lctl -c /dev/video2 movie fps 29.97
> and then "xawtv"
>
> When I start xawtv it says it's getting audio from hw:3,0
>
> When I said above "I can watch" I meant "xawtv works completely, with both
sound and video"
However, as outlined below, none of the other attempts I've made seem to be
able to get at that sound.
So, yes, the audio hardware is demonstrably working fine "end to end".

One kind commenter noted that I could grab sound from another source.
That's true, and does work, but it's way out of sync, so if I can make this
work all on the one piece of hardware, that would be preferable.


> I can also play the video, but *without*sound* using:
>
> ffplay -f v4l2 -i /dev/video2 -vf yadif
>
> and the picture is just great (well, for a home movie on VHS tape, at
> least!) but I get no sounds from this.
>
> I have tried capturing in a variety of formats, but always end up with a
> silent sound-track (if I don't specify explicitly that I want -f alsa and
> some audio source, I don't even get a sound track). Anway, there seems
> little point in dumping the output of half a dozen failures, This one I
> think is representative: If I try to do ffplay directly on the audio using:
>
> ffplay -f alsa -i plughw:3,0
>
> I get a black window (not surprising, I didn't specify a video source!),
> silence, and the following output that runs for as long as I let it until I
> kill it with control-c.
>
> $ ffplay -f alsa -i plughw:3,0
> ffplay version 4.2.4-1ubuntu0.1 Copyright (c) 2003-2020 the FFmpeg
> developers
>   built with gcc 9 (Ubuntu 9.3.0-10ubuntu2)
>   configuration: --prefix=/usr --extra-version=1ubuntu0.1
> --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu
> --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl
> --disable-stripping --enable-avresample --disable-filter=resample
> --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom
> --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca
> --enable-libcdio --enable-libcodec2 --enable-libflite
> --enable-libfontconfig --enable-libfreetype --enable-libfribidi
> --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame
> --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt
> --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband
> --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex
> --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab
> --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp
> --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq
> --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl
> --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm
> --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r
> --enable-libx264 --enable-shared
>   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
> Input #0, alsa, from 'plughw:3,0': 0KB vq=    0KB sq=    0B f=0/0
>   Duration: N/A, start: 1598560765.378207, bitrate: 1536 kb/s
>     Stream #0:0: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s
> 1598560779.36 M-A:  0.000 fd=   0 aq=    0KB vq=    0KB sq=    0B f=0/0
>
> it seems to think there's "something there" (it doesn't reject
> "plughw:3,0" as bogus) and to have detected something with a format, yet,
> nothing.
>
> Any idea how to proceed? Can I get more information from xawtv perhaps
> that might help me know how it's succeeding and transfer that info to
> ffmpeg?
>
>
>