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• Alsa audio playback program occurs underrun errors frequency

  15 juillet 2021, par Tank2006

  My environment is Raspberry Pi 3B/Raspberry Pi OS, and I'm building remotely from Visual Studio 2019 on Windows 10.

  


  I want to play PCM audio decoded by FFmpeg in ALSA(C language API).
But this code returns Underrun error(EPIPE) at "snd_pcm_writei" and plays a cracky sound.

  


  Probably the way the resources are managed is wrong, but I don't know how to optimize it.

  


  avres AlsaPlayer::OpenOutputDevice(AlsaDeviceType ao_type, OutputMode omode)
{
    memset(&output_format, 0, sizeof(InterfaceFormat));

    avres res;

    string dname = GetAlsaDeviceName(false, (ao_type == AD_DIGITAL));
    res = snd_pcm_open(&play_handle, dname.c_str(), SND_PCM_STREAM_PLAYBACK, 0);

    if (AV_FAILED(res)) return res;

    unsigned int sample_rate = DEFAULT_OUTPUT_RATE;
    uint64_t ch_layout = (ao_type == AD_ANALOG_6CH) ? AV_CH_LAYOUT_5POINT1 : AV_CH_LAYOUT_STEREO;
    int channels = av_get_channel_layout_nb_channels(ch_layout);

    snd_pcm_hw_params_t *hw_params;
    res = snd_pcm_hw_params_malloc(&hw_params);

    snd_pcm_hw_params_any(play_handle, hw_params);

    res = snd_pcm_hw_params_set_access(play_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED);
    res = snd_pcm_hw_params_set_format(play_handle, hw_params, SND_PCM_FORMAT_S16_LE);
    res = snd_pcm_hw_params_set_channels(play_handle, hw_params, channels);
    res = snd_pcm_hw_params_set_rate_near(play_handle, hw_params, &sample_rate, 0);
    res = snd_pcm_hw_params(play_handle, hw_params);

    snd_pcm_uframes_t frames; 
    snd_pcm_hw_params_get_period_size(hw_params, &frames, 0);
    snd_pcm_hw_params_get_period_time(hw_params, &out_period_time, 0);

    snd_pcm_hw_params_free(hw_params);

    if (AV_FAILED(res)) return res;

    output_format.channels = channels;
    output_format.ch_layout = ch_layout;
    output_format.format = AV_SAMPLE_FMT_S16;
    output_format.frame_size = channels * 16 / 8;
    output_format.mode.output = omode;
    output_format.sample_rate = sample_rate;

    out_period_size = (int)frames * output_format.frame_size;
    out_buf_size = 10 * out_period_size;
    output_fifo = av_fifo_alloc(out_buf_size);

    return res;
}

void AlsaPlayer::RenderThread()
{
    while (av_fifo_size(output_fifo) == 0) usleep(1000);

    avres res;
    int frame_size = (output_format.mode.output == OutputMode::Analog) ? output_format.frame_size : 4;
    uint8_t *dst = new uint8_t[out_buf_size];
    while (need_exit == false) {
        int sz = FFMIN(out_buf_size, av_fifo_size(output_fifo));
        int frames = sz / frame_size;
        if (sz > frame_size) {
            res = av_fifo_generic_read(output_fifo, dst, sz, nullptr);
            res = (int)snd_pcm_writei(play_handle, dst, frames);

            if (AV_FAILED(res)) {
                if (AV_FAILED(snd_pcm_recover(play_handle, res, 0))) {
                    need_exit = true;
                    SendComErrorMessage(false, res, "dest_device_error");
                    break;
                }
            }
        }
    }
    delete[]dst;
}


  


  Can I pick your brains ?

  


• DE-10 FFMPEG Raw YCbCr 4:2:2 Frame to PNG or Video leads to bad result

  22 mai 2021, par Anouar Touati

  So i am trying to record analog video from analog-video in port of the DE10-standard board.

  


  the raw frames are 4:2:2 720x480 hence frame size should be 720*480 * 2 = 691200bytes,however i get 2 more bytes with hex value 0 at the beginning of the frametwo leading bytes.

  


  ffmpeg complains about wrong buffer size so i removed them.

  


  using ffmpeg -y -s 720x480 -pix_fmt yuv422p -i input_frame.yuv output_image.png
the result is way off.

  


  analog video fed to the board has still image (photo taken by phone from TV) Reference Pic.
and the result from ffmpeg is FFMPEG output.

  


  i used HxD editor and mirrored that single frame many times to create a larger file then used the following command to encode it to MP4 file which give the same result.

  


  ffmpeg -y -s 720x480 -pix_fmt yuv422p -i dump_video.yuv output_video.mp4.

  


  i hope someone can help to fix the issue or point me in the right direction as i dont know if the problem is from hardware or from ffmpeg command. Thnx.

  


• Using ffmpeg on Ubuntu, how can the audio and video from an audio-video USB capture device be recorded ?

  11 avril 2022, par BlandCorporation

  I have a USB audio-video capture device, something used to digitize video cassettes. I want to record both the video and audio from the device to a video file that has dimensions 720x576 and video codec H.264 and good audio quality.

  


  I am able to record video from the device using ffmpeg and I am able to see video from the device using MPlayer. I am able also to see that audio is being delivered from the device to the computer by looking at Input tab of the Sound Preferences window or by recording the audio using Audacity, however the audio gets delivered from the device apparently only when the video is being accessed using ffmpeg or MPlayer.

  


  I have tried to get ffmpeg to record the audio and I have tried to get MPlayer to play the audio and my efforts have not been successful.

  


  The device is "Pinnacle Dazzle DVC 90/100/101" (as returned by v4l2-ctl --list-devices). The sound cards listing shows it as "DVC100" :

  


  $ cat /proc/asound/cards 
 0 [PCH            ]: HDA-Intel - HDA Intel PCH
                      HDA Intel PCH at 0x601d118000 irq 171
 1 [DVC100         ]: USB-Audio - DVC100
                      Pinnacle Systems GmbH DVC100 at usb-0000:00:14.0-4, high speed
29 [ThinkPadEC     ]: ThinkPad EC - ThinkPad Console Audio Control
                      ThinkPad Console Audio Control at EC reg 0x30, fw N2LHT33W


  


  The PulseAudio listing for the device is as follows :

  


  $ pactl list cards short
0   alsa_card.pci-0000_00_1f.3  module-alsa-card.c
14  alsa_card.usb-Pinnacle_Systems_GmbH_DVC100-01   module-alsa-card.c


  


  The following ffmpeg command successfully records video, but records severely distorted, broken and out-of-sync audio :

  


  ffmpeg -y -f rawvideo -f alsa -thread_queue_size 2048 -ar 48000 -i hw:0 \
    -c:a aac -video_size 720x576 -pixel_format uyvy422 -i /dev/video2 out.mp4


  


  The following MPlayer command successfully displays the video but does not play the audio :

  


  mplayer -tv driver=v4l2:norm=PAL:device=/dev/video2:width=720:height=576 \
    -ao alsa:device=hw=1.0 -vf pp=lb tv://


  


  Now, when the above MPlayer command is running (not the ffmpeg command) and displaying the input video in a window, Audacity can be opened and set recording audio, and it records the audio from the device clearly and in good quality. While Audacity is doing this, the input device is listed in pavucontrol as "Dazzle DVC Audio Device Analogue Stereo". Equivalently, arecord can be used also to record the audio using the following command (with output shown) :

  


  $ arecord -vv -D plughw:DVC100 -fdat out.wav
Recording WAVE 'out.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Plug PCM: Hardware PCM card 1 'DVC100' device 0 subdevice 0
Its setup is:
  stream       : CAPTURE
  access       : RW_INTERLEAVED
  format       : S16_LE
  subformat    : STD
  channels     : 2
  rate         : 48000
  exact rate   : 48000 (48000/1)
  msbits       : 16
  buffer_size  : 24000
  period_size  : 6000
  period_time  : 125000
  tstamp_mode  : NONE
  tstamp_type  : MONOTONIC
  period_step  : 1
  avail_min    : 6000
  period_event : 0
  start_threshold  : 1
  stop_threshold   : 24000
  silence_threshold: 0
  silence_size : 0
  boundary     : 6755399441055744000
  appl_ptr     : 0
  hw_ptr       : 0


  


  Looking at the output of arecord -L, I tried a variety of audio device input names with ffmpeg and none of them seemed to work. So, for example, I tried commands like the following :

  


  ffmpeg -y -f rawvideo -f alsa -i plughw:DVC100 \
    -video_size 720x576 -pixel_format uyvy422 -i /dev/video2 out.mp4


  


  And tried the following audio device names :

  


  plughw:DVC100
plughw:CARD=DVC100,DEV=0
hw:CARD=DVC100,DEV=0
plughw:CARD=DVC100
sysdefault:CARD=DVC100
iec958:CARD=DVC100,DEV=0
dsnoop:CARD=DVC100,DEV=0


  


  So, how might I get ffmpeg to record the audio successfully to the video file ? Is there some alternative approach to this problem ?

  


  ---

  


  EDIT : The relevant output from the command pactl list sources is as follows :

  


  Source #20
    State: SUSPENDED
    Name: alsa_input.usb-Pinnacle_Systems_GmbH_DVC100-01.analog-stereo
    Description: Dazzle DVC100 Audio Device Analogue Stereo
    Driver: module-alsa-card.c
    Sample Specification: s16le 2ch 48000Hz
    Channel Map: front-left,front-right
    Owner Module: 45
    Mute: no
    Volume: front-left: 99957 / 153% / 11.00 dB,   front-right: 99957 / 153% / 11.00 dB
            balance 0.00
    Base Volume: 35466 /  54% / -16.00 dB
    Monitor of Sink: n/a
    Latency: 0 usec, configured 0 usec
    Flags: HARDWARE HW_MUTE_CTRL HW_VOLUME_CTRL DECIBEL_VOLUME LATENCY 
    Properties:
        alsa.resolution_bits = "16"
        device.api = "alsa"
        device.class = "sound"
        alsa.class = "generic"
        alsa.subclass = "generic-mix"
        alsa.name = "USB Audio"
        alsa.id = "USB Audio"
        alsa.subdevice = "0"
        alsa.subdevice_name = "subdevice #0"
        alsa.device = "0"
        alsa.card = "1"
        alsa.card_name = "DVC100"
        alsa.long_card_name = "Pinnacle Systems GmbH DVC100 at usb-0000:00:14.0-4, high speed"
        alsa.driver_name = "snd_usb_audio"
        device.bus_path = "pci-0000:00:14.0-usb-0:4:1.1"
        sysfs.path = "/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.1/sound/card1"
        udev.id = "usb-Pinnacle_Systems_GmbH_DVC100-01"
        device.bus = "usb"
        device.vendor.id = "2304"
        device.vendor.name = "Pinnacle Systems, Inc."
        device.product.id = "021a"
        device.product.name = "Dazzle DVC100 Audio Device"
        device.serial = "Pinnacle_Systems_GmbH_DVC100"
        device.string = "front:1"
        device.buffering.buffer_size = "352800"
        device.buffering.fragment_size = "176400"
        device.access_mode = "mmap+timer"
        device.profile.name = "analog-stereo"
        device.profile.description = "Analogue Stereo"
        device.description = "Dazzle DVC100 Audio Device Analogue Stereo"
        alsa.mixer_name = "USB Mixer"
        alsa.components = "USB2304:021a"
        module-udev-detect.discovered = "1"
        device.icon_name = "audio-card-usb"
    Ports:
        analog-input-linein: Line In (priority: 8100)
    Active Port: analog-input-linein
    Formats:
        pcm


  


  I tested the name from this with ffmpeg (version 4.3.1, compiled with -enable-libpulse) in the following way :

  


  ffmpeg -y -f video4linux2 -f pulse \
    -i alsa_input.usb-Pinnacle_Systems_GmbH_DVC100-01.analog-stereo \
    -video_size 720x576 -pixel_format uyvy422 -i /dev/video2 out.mp4


  


  Unfortunately this hasn't worked.