[vlc-devel] [Patch] Implementing MP4 DEMUX_GET_FPS control query

[Hugo Beauzee-Luyssen]

On Sat, Sep 5, 2009 at 11:08 AM, Laurent Aimar<fenrir at via.ecp.fr> wrote:
> Hi,
>
> On Fri, Sep 04, 2009, Hugo Beauzee-Luyssen wrote:
>> The mp4 demuxer's DEMUX_GET_FPS control query wasn't implemented,
>> which was preventing libvlc_media_player_get_fps to access the fps.
>> This patch corrects it.
>
>> From 4926a669a00f7bd6639086835655dc7bd3ca22ae Mon Sep 17 00:00:00 2001
>> From: Hugo Beauzee-Luyssen <beauze.h at gmail.com>
>> Date: Fri, 4 Sep 2009 00:41:36 +0200
>> Subject: [PATCH] Implementing MP4 DEMUX_GET_FPS control query
>>
>> ---
>>  modules/demux/mp4/mp4.c |    8 ++++++--
>>  1 files changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/modules/demux/mp4/mp4.c b/modules/demux/mp4/mp4.c
>> index 76aa37c..ebb6023 100644
>> --- a/modules/demux/mp4/mp4.c
>> +++ b/modules/demux/mp4/mp4.c
>> @@ -155,6 +155,7 @@ struct demux_sys_t
>>      uint64_t     i_duration;     /* movie duration */
>>      unsigned int i_tracks;       /* number of tracks */
>>      mp4_track_t  *track;         /* array of track */
>> +    float        f_fps;          /* number of frame per seconds */
>>
>>      /* */
>>      MP4_Box_t    *p_tref_chap;
>> @@ -837,8 +838,9 @@ static int Control( demux_t *p_demux, int i_query, va_list args )
>>              return VLC_SUCCESS;
>>
>>          case DEMUX_GET_FPS:
>> -            msg_Warn( p_demux, "DEMUX_GET_FPS unimplemented !!" );
>> -            return VLC_EGENERIC;
>> +            pf = (double*)va_arg( args, double* );
>> +            *pf = (double)p_sys->f_fps;
>> +            return VLC_SUCCESS;
>>
>>          case DEMUX_GET_META:
>>          {
>> @@ -1518,6 +1520,8 @@ static int TrackCreateES( demux_t *p_demux, mp4_track_t *p_track,
>>              p_track->fmt.video.i_frame_rate_base =
>>                  p_box->data.p_stts->i_sample_delta[0];
>>          }
>> +        p_demux->p_sys->f_fps = (float)p_track->i_timescale /
>> +                                (float)p_track->fmt.video.i_frame_rate_base;
>  It would be more coherent to use p_track->fmt.video.i_frame_rate instead
> of p_track->i_timescale.
>
>  Now, I highly doubt it work well on a lot of files, i_timescale is not bound to
> represent the frame rate at all.
>  I think the most reliable way would be to count the number of frames and the total
> duration to estimate the frame rate. I think that the last message in
> TrackCreateSamplesIndex use the needed informations (but I am not sure).
>
> Regards,
>

Well... this is how the FPS shown in the codec information window is computed.
Moreover, p_track->fmt.video.i_frame_rate is just the i_timescale value.
If this is not the right way of computing a frame rate, I'd say the
frame rate displayed in the codec information window isn't computed
correctly either.

-- 
Hugo Beauzée-Luyssen