[vlc-devel] [PATCH] Flaschen Taschen output: Support for large(r) video sizes

[Rémi Denis-Courmont]

Hi,

Le lauantaina 25. huhtikuuta 2020, 11.06.20 EEST Johannes Lechner a écrit :
> This patches contains two modifications to make Flaschen Taschen support
> large(r) video sizes: (1) Increase of UDP send buffer, allowing
> maximum-sized UDP packets to be sent

Increasing the send buffer seems pointless here. Not like it'll magically 
increase bandwidth. Just wait for buffer space to send the next packet. Either 
leave the socket in blocking mode, or poll for output.

> (2) Splitting a frame into multiple
> UDP packets in case one frame exceeds the maximum UDP packet size

That's good, but I don't really follow how it works here. How does the 
receiver know which packet belongs to which frame?

> 
> The implemention for (2) draws heavily from the "official"
> UDPFlaschenTaschen::Send implemention:
> https://github.com/hzeller/flaschen-taschen/blob/master/api/lib/udp-flasche
> n-taschen.cc ---
>  modules/video_output/flaschen.c | 113 +++++++++++++++++++-------------
>  1 file changed, 66 insertions(+), 47 deletions(-)
> 
> diff --git a/modules/video_output/flaschen.c
> b/modules/video_output/flaschen.c index 00e1e66a34..b9f541dc30 100644
> --- a/modules/video_output/flaschen.c
> +++ b/modules/video_output/flaschen.c
> @@ -134,8 +134,9 @@ static int Open(vout_display_t *vd, const
> vout_display_cfg_t *cfg,
> 
>      /* Ignore any unexpected incoming packet */
>      setsockopt (fd, SOL_SOCKET, SO_RCVBUF, &(int){ 0 }, sizeof (int));
> -
> -
> +    /* Increase send buffer size to allow queuing of several "full" UDP
> packets  */ +    setsockopt (fd, SOL_SOCKET, SO_SNDBUF, &(int){ 16 * 65536
> }, sizeof (int)); +
>      *fmtp = fmt;
> 
>      vd->prepare = NULL;
> @@ -155,55 +156,73 @@ static void Close(vout_display_t *vd)
>      free(sys);
>  }
> 
> +/*
> + * Adaptation of UDPFlaschenTaschen::Send implemention
> + * (https://github.com/hzeller/flaschen-taschen/)
> + */
>  static void Display(vout_display_t *vd, picture_t *picture)
>  {
> -#ifdef IOV_MAX
> -    const long iovmax = IOV_MAX;
> -#else
> -    const long iovmax = sysconf(_SC_IOV_MAX);
> -#endif
> -    vout_display_sys_t *sys = vd->sys;
> -    video_format_t *fmt = &picture->format;
> -    int result;
> -
> -    char buffer[64];
> -    int header_len = snprintf(buffer, sizeof(buffer), "P6\n%d %d\n255\n",
> -                              fmt->i_width, fmt->i_height);
> -    /* TODO: support offset_{x,y,z}? (#FT:...) */
> -    /* Note the protocol doesn't include any picture order field. */
> -    /* (maybe add as comment?) */
> -
> -    int iovcnt = 1 + fmt->i_height;
> -    if (unlikely(iovcnt > iovmax))
> -        return;
> -
> -    struct iovec iov[iovcnt];
> -    iov[0].iov_base = buffer;
> -    iov[0].iov_len = header_len;
> -
> -    uint8_t *src = picture->p->p_pixels;
> -    for (int i = 1; i < iovcnt; i++)
> +    video_format_t *format = &picture->format;
> +    uint8_t *pixels = picture->p->p_pixels;
> +
> +    const int max_data_packet_length = 65507 - 64;  // Leave some space for
> the P6 header +    const size_t row_size = format->i_width * 3;
> +    const int max_send_height = max_data_packet_length / row_size;
> +
> +    int rows = format->i_height;
> +    int row_offset = 0;
> +
> +    while(rows)
>      {
> -        iov[i].iov_base = src;
> -        iov[i].iov_len = fmt->i_width * 3;
> -        src += picture->p->i_pitch;
> +        // Send as many rows as can fit within one UDP packet
> +        const int send_height = (rows < max_send_height) ? rows :
> max_send_height; +
> +        char p6_header[64];
> +        const int p6_header_len = snprintf(p6_header, sizeof(p6_header),
> +                                           "P6\n%d %d\n#FT: %d %d
> %d\n255\n", +                                           format->i_width,
> send_height, +                                           0, row_offset, 0);
> +        //msg_Dbg(vd, "p6_header: %s", p6_header`);
> +
> +        const int p6_data_len = send_height * row_size;
> +
> +        // Create and send UDP packet
> +        {
> +            struct iovec iov[2];
> +            iov[0].iov_base = p6_header;
> +            iov[0].iov_len = p6_header_len;
> +            iov[1].iov_base = pixels;
> +            iov[1].iov_len = p6_data_len;
> +
> +            struct msghdr hdr = {
> +                .msg_name = NULL,
> +                .msg_namelen = 0,
> +                .msg_iov = iov,
> +                .msg_iovlen = 2,
> +                .msg_control = NULL,
> +                .msg_controllen = 0,
> +                .msg_flags = 0 };
> +
> +            int result;
> +            result = sendmsg(vd->sys->fd, &hdr, 0);
> +
> +            if (result < 0) {
> +                msg_Err(vd, "sendmsg: error %s in vout display flaschen,
> dropping remainder of frame", vlc_strerror_c(errno)); +                //
> dropping remainder of frame
> +                break;
> +            }
> +            else if (result < (int)(p6_header_len + p6_data_len)) {
> +                msg_Err(vd, "sendmsg only sent %d bytes in vout display
> flaschen, dropping remainder of frame", result); +                //
> dropping remainder of frame
> +                break;
> +            }
> +        }
> +
> +        pixels += p6_data_len;
> +
> +        rows -= send_height;
> +        row_offset += send_height;
>      }
> -
> -    struct msghdr hdr = {
> -        .msg_name = NULL,
> -        .msg_namelen = 0,
> -        .msg_iov = iov,
> -        .msg_iovlen = iovcnt,
> -        .msg_control = NULL,
> -        .msg_controllen = 0,
> -        .msg_flags = 0 };
> -
> -    result = sendmsg(sys->fd, &hdr, 0);
> -    if (result < 0)
> -        msg_Err(vd, "sendmsg: error %s in vout display flaschen",
> vlc_strerror_c(errno)); -    else if (result < (int)(header_len +
> fmt->i_width * fmt->i_height * 3)) -        msg_Err(vd, "sendmsg only sent
> %d bytes in vout display flaschen", result); -        /* we might want to
> drop some frames? */
>  }
> 
>  /**


-- 
Rémi Denis-Courmont
http://www.remlab.net/