[vlc-devel] [vlc-commits] ytdl: improve format selection

[Steve Lhomme]

While it's surely an improvement on the module, I think it's still wrong 
to provide a single version of the stream where there are plenty and the 
adaptive code is better suited to select the proper one at any given time.

Also do these streams provide both audio and video in a single stream ? 
 From my own tests in Lua it seems most fancy formats only have either 
audio or video but not both (including testing with youtube-dl -F). This 
makes the whole script very limited, at least for YouTube. And again the 
adaptive streaming code can handle this case as that's how adaptive 
streaming works in many cases.

On 2020-09-29 18:16, Rémi Denis-Courmont wrote:
> vlc | branch: master | Rémi Denis-Courmont <remi at remlab.net> | Tue Sep 29 19:15:46 2020 +0300| [5e9ceb894f8124282383e1d48d798143225acada] | committer: Rémi Denis-Courmont
> 
> ytdl: improve format selection
> 
>> http://git.videolan.org/gitweb.cgi/vlc.git/?a=commit;h=5e9ceb894f8124282383e1d48d798143225acada
> ---
> 
>   modules/demux/ytdl.c | 61 +++++++++++++++++++++++++++++++++++++++++-----------
>   1 file changed, 49 insertions(+), 12 deletions(-)
> 
> diff --git a/modules/demux/ytdl.c b/modules/demux/ytdl.c
> index a6dce10213..8b21b067ee 100644
> --- a/modules/demux/ytdl.c
> +++ b/modules/demux/ytdl.c
> @@ -79,6 +79,47 @@ struct ytdl_playlist {
>       stream_t *source;
>   };
>   
> +
> +static int CompareFormats(const struct json_object *f_a,
> +                          const struct json_object *f_b, double pref_height)
> +{
> +    double h_a = json_get_num(f_a, "height");
> +    double abr_a = json_get_num(f_a, "abr");
> +    double h_b = json_get_num(f_b, "height");
> +    double abr_b = json_get_num(f_b, "abr");
> +
> +    /* Prefer non-mute formats */
> +    if (!isnan(abr_a) != !isnan(abr_b))
> +        return isnan(abr_a) ? -1 : +1;
> +
> +    /* Prefer non-blind formats */
> +    if (!isnan(h_a) != !isnan(h_b))
> +        return isnan(h_a) ? -1 : +1;
> +
> +    if (islessequal(h_a, pref_height)) {
> +        if (!islessequal(h_b, pref_height))
> +            return +1;
> +        if (h_a > h_b)
> +            return -1;
> +        if (h_a < h_b)
> +            return +1;
> +    } else {
> +        if (islessequal(h_b, pref_height))
> +            return -1;
> +        if (isless(h_a, h_b))
> +            return -1;
> +        if (isgreater(h_a, h_b))
> +            return +1;
> +    }
> +
> +    if (isgreater(abr_a, abr_b))
> +        return +1;
> +    if (isgreater(abr_b, abr_a))
> +        return -1;
> +
> +    return 0;
> +}
> +
>   static const struct json_object *PickFormat(stream_t *s,
>                                               const struct json_object *entry)
>   {
> @@ -91,8 +132,9 @@ static const struct json_object *PickFormat(stream_t *s,
>   
>        const struct json_object *best_fmt = NULL;
>        double pref_height = var_InheritInteger(s, "preferred-resolution");
> -     double best_height = -1.;
> -     double best_abr = -1.;
> +
> +     if (isless(pref_height, 0.))
> +         pref_height = NAN;
>   
>        for (size_t i = 0; i < fmts->array.size; i++) {
>            const struct json_value *v = &fmts->array.entries[i];
> @@ -101,19 +143,14 @@ static const struct json_object *PickFormat(stream_t *s,
>                continue;
>   
>            const struct json_object *fmt = &v->object;
> -         double height = json_get_num(fmt, "height");
> -         double abr = json_get_num(fmt, "abr");
>   
> -         if (!isgreaterequal(height, best_height)
> -          || (best_height < pref_height && pref_height < height))
> -             continue;
> -
> -         if (!isgreaterequal(abr, best_abr))
> +         if (best_fmt == NULL) {
> +             best_fmt = fmt;
>                continue;
> +         }
>   
> -         best_fmt = fmt;
> -         best_height = height;
> -         best_abr = abr;
> +         if (CompareFormats(fmt, best_fmt, pref_height) > 0)
> +              best_fmt = fmt;
>        }
>   
>        return best_fmt;
> 
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