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

[Hugo Beauzee-Luyssen]

On Sat, Sep 5, 2009 at 11:33 PM, Hugo Beauzee-Luyssen<beauze.h at gmail.com> wrote:
> 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
>

Any other feedbacks or comments ?

Regards,

-- 
Hugo Beauzée-Luyssen