[FFmpeg-devel] [PATCH 1/2] lavd/alsa: fix timestamp calculation

[Nicolas George]

Le quintidi 5 brumaire, an CCXXII, Lukasz M a écrit :
> From 3d7590ed1d012367f0e1408efa4b629d6343220c Mon Sep 17 00:00:00 2001
> From: Lukasz Marek <lukasz.m.luki at gmail.com>
> Date: Sat, 26 Oct 2013 01:19:31 +0200
> Subject: [PATCH 1/2] lavd/alsa: fix timestamp calculation
> 
> Current implementation didn't include duration of
> last processed packet.
> Device may return negative timestamps without
> this correction.
> 
> Signed-off-by: Lukasz Marek <lukasz.m.luki at gmail.com>
> ---
>  libavdevice/alsa-audio-enc.c |    9 ++++++++-
>  libavdevice/alsa-audio.h     |    1 +
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/libavdevice/alsa-audio-enc.c b/libavdevice/alsa-audio-enc.c
> index 0f4e4a2..2239046 100644
> --- a/libavdevice/alsa-audio-enc.c
> +++ b/libavdevice/alsa-audio-enc.c
> @@ -79,6 +79,13 @@ static int audio_write_packet(AVFormatContext *s1, AVPacket *pkt)
>      int size     = pkt->size;
>      uint8_t *buf = pkt->data;
>  
> +    if (!(s->timestamp_diff = pkt->duration)) {
> +        AVStream *st = s1->streams[0];
> +        AVCodecContext *codec_ctx = st->codec;
> +        /* XXX: no need to recalculate: 1/sample_rate == avpriv_set_pts_info() */

> +        s->timestamp_diff = pkt->size / (av_get_bytes_per_sample(codec_ctx->sample_fmt) * codec_ctx->channels);

The number of bytes per sample is already in s->frame_size. In fact:

> +    }
> +
>      size /= s->frame_size;

... the duration is precisely "size" now.

Therefore, you could probably just write:

    s->timestamp_diff = pkt->duration ? pkt->duration : size;

(and curse C not to be able to write "pkt->duration || size").

>      if (s->reorder_func) {
>          if (size > s->reorder_buf_size)
> @@ -112,7 +119,7 @@ audio_get_output_timestamp(AVFormatContext *s1, int stream,
>      snd_pcm_sframes_t delay = 0;
>      *wall = av_gettime();
>      snd_pcm_delay(s->h, &delay);
> -    *dts = s1->streams[0]->cur_dts - delay;
> +    *dts = s1->streams[0]->cur_dts + s->timestamp_diff - delay;
>  }
>  
>  AVOutputFormat ff_alsa_muxer = {
> diff --git a/libavdevice/alsa-audio.h b/libavdevice/alsa-audio.h
> index 44b7c72..005cf83 100644
> --- a/libavdevice/alsa-audio.h
> +++ b/libavdevice/alsa-audio.h
> @@ -57,6 +57,7 @@ typedef struct AlsaData {
>      void (*reorder_func)(const void *, void *, int);
>      void *reorder_buf;
>      int reorder_buf_size; ///< in frames
> +    int64_t timestamp_diff; ///< duration of last packet, needed to calculate timestamp
>  } AlsaData;
>  
>  /**

Apart from that simplification, it looks right, thanks.

Regards,

-- 
  Nicolas George
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 836 bytes
Desc: Digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20131026/4a2d2db3/attachment.asc>