Re: [FFmpeg-devel] [PATCH 08/11] fftools/opt_common: switch to avcodec_get_supported_config()

[Niklas Haas <ffmpeg@haasn.xyz>]

On Fri, 05 Apr 2024 16:36:50 -0300 James Almer <jamrial@gmail.com> wrote:
> On 4/5/2024 3:57 PM, Niklas Haas wrote:
> > From: Niklas Haas <git@haasn.dev>
> > 
> > While rewriting this macro, I decided to make it a bit more flexible so
> > it can work for all of the fields (including future fields) in a more
> > generic way.
> > ---
> >   fftools/opt_common.c | 86 ++++++++++++++++++++++----------------------
> >   1 file changed, 43 insertions(+), 43 deletions(-)
> > 
> > diff --git a/fftools/opt_common.c b/fftools/opt_common.c
> > index 947a226d8d1..1bf66580192 100644
> > --- a/fftools/opt_common.c
> > +++ b/fftools/opt_common.c
> > @@ -262,22 +262,32 @@ int show_buildconf(void *optctx, const char *opt, const char *arg)
> >       return 0;
> >   }
> >   
> > -#define PRINT_CODEC_SUPPORTED(codec, field, type, list_name, term, get_name) \
> > -    if (codec->field) {                                                      \
> > -        const type *p = codec->field;                                        \
> > -                                                                             \
> > -        printf("    Supported " list_name ":");                              \
> > -        while (*p != term) {                                                 \
> > -            get_name(*p);                                                    \
> > -            printf(" %s", name);                                             \
> > -            p++;                                                             \
> > -        }                                                                    \
> > -        printf("\n");                                                        \
> > -    }                                                                        \
> > +#define PRINT_CODEC_SUPPORTED(codec, config, type, name, elem, cond, fmt, ...)  \
> > +    do {                                                                        \
> > +        const type *elem = NULL;                                                \
> > +        avcodec_get_supported_config(NULL, codec, config, 0,                    \
> > +                                     (const void **) &elem);                    \
> > +        if (elem) {                                                             \
> > +            printf("    Supported " name ":");                                  \
> > +            while (cond) {                                                      \
> > +                printf(" " fmt, __VA_ARGS__);                                   \
> > +                elem++;                                                         \
> > +            }                                                                   \
> > +            printf("\n");                                                       \
> > +        }                                                                       \
> > +    } while (0)
> > +
> > +static char *get_channel_layout_desc(const AVChannelLayout *layout,
> > +                                     char desc[], int desc_size)
> > +{
> > +    av_channel_layout_describe(layout, desc, desc_size);
> > +    return desc;
> > +}
> >   
> >   static void print_codec(const AVCodec *c)
> >   {
> >       int encoder = av_codec_is_encoder(c);
> > +    char desc[128];
> >   
> >       printf("%s %s [%s]:\n", encoder ? "Encoder" : "Decoder", c->name,
> >              c->long_name ? c->long_name : "");
> > @@ -343,35 +353,19 @@ static void print_codec(const AVCodec *c)
> >           printf("\n");
> >       }
> >   
> > -    if (c->supported_framerates) {
> > -        const AVRational *fps = c->supported_framerates;
> > -
> > -        printf("    Supported framerates:");
> > -        while (fps->num) {
> > -            printf(" %d/%d", fps->num, fps->den);
> > -            fps++;
> > -        }
> > -        printf("\n");
> > -    }
> > -    PRINT_CODEC_SUPPORTED(c, pix_fmts, enum AVPixelFormat, "pixel formats",
> > -                          AV_PIX_FMT_NONE, GET_PIX_FMT_NAME);
> > -    PRINT_CODEC_SUPPORTED(c, supported_samplerates, int, "sample rates", 0,
> > -                          GET_SAMPLE_RATE_NAME);
> > -    PRINT_CODEC_SUPPORTED(c, sample_fmts, enum AVSampleFormat, "sample formats",
> > -                          AV_SAMPLE_FMT_NONE, GET_SAMPLE_FMT_NAME);
> > -
> > -    if (c->ch_layouts) {
> > -        const AVChannelLayout *p = c->ch_layouts;
> > -
> > -        printf("    Supported channel layouts:");
> > -        while (p->nb_channels) {
> > -            char name[128];
> > -            av_channel_layout_describe(p, name, sizeof(name));
> > -            printf(" %s", name);
> > -            p++;
> > -        }
> > -        printf("\n");
> > -    }
> > +    PRINT_CODEC_SUPPORTED(c, AV_CODEC_CONFIG_FRAME_RATE, AVRational, "framerates",
> > +                          fps, fps->num, "%d/%d", fps->num, fps->den);
> > +    PRINT_CODEC_SUPPORTED(c, AV_CODEC_CONFIG_PIX_FORMAT, enum AVPixelFormat,
> > +                          "pixel formats", fmt, *fmt != AV_PIX_FMT_NONE,
> > +                          "%s", av_get_pix_fmt_name(*fmt));
> > +    PRINT_CODEC_SUPPORTED(c, AV_CODEC_CONFIG_SAMPLE_RATE, int, "sample rates",
> > +                          rate, *rate != 0, "%d", *rate);
> > +    PRINT_CODEC_SUPPORTED(c, AV_CODEC_CONFIG_SAMPLE_FORMAT, enum AVSampleFormat,
> > +                          "sample formats", fmt, *fmt != AV_SAMPLE_FMT_NONE,
> > +                          "%s", av_get_sample_fmt_name(*fmt));
> > +    PRINT_CODEC_SUPPORTED(c, AV_CODEC_CONFIG_CHANNEL_LAYOUT, AVChannelLayout,
> > +                          "channel layouts", layout, layout->nb_channels,
> > +                          "%s", get_channel_layout_desc(layout, desc, sizeof(desc)));
> 
> Since you're rewriting everything, might as well go and port this to 
> AVBprint, so we're not limited to 128 bytes for the channel layout.
> You can use av_bprintf() to write to the buffer using the different 
> specifiers, then printf() the final bprint buffer to stdout.

I implemented something like this initially, but it is IMO premature
optimization as there is no multi-threading going on in this code, so no
risk of colliding printf() calls. printf() already internally buffers
data, so we are not gaining anything by buffering it inside an AVBPrint
a second time.

That said, using an AVBPrint instead of a fixed size buffer is a good
idea for the channel layout specifically, something like this:


diff --git a/fftools/opt_common.c b/fftools/opt_common.c
index 1bf66580192..fae68949f89 100644
--- a/fftools/opt_common.c
+++ b/fftools/opt_common.c
@@ -277,17 +277,17 @@ int show_buildconf(void *optctx, const char *opt, const char *arg)
         }                                                                       \
     } while (0)
 
-static char *get_channel_layout_desc(const AVChannelLayout *layout,
-                                     char desc[], int desc_size)
+static char *get_channel_layout_desc(const AVChannelLayout *layout, AVBPrint *bp)
 {
-    av_channel_layout_describe(layout, desc, desc_size);
-    return desc;
+    av_bprint_clear(bp);
+    av_channel_layout_describe_bprintf(layout, bp);
+    return bp->str;
 }
 
 static void print_codec(const AVCodec *c)
 {
     int encoder = av_codec_is_encoder(c);
-    char desc[128];
+    AVBPrint desc;
 
     printf("%s %s [%s]:\n", encoder ? "Encoder" : "Decoder", c->name,
            c->long_name ? c->long_name : "");
@@ -363,9 +363,12 @@ static void print_codec(const AVCodec *c)
     PRINT_CODEC_SUPPORTED(c, AV_CODEC_CONFIG_SAMPLE_FORMAT, enum AVSampleFormat,
                           "sample formats", fmt, *fmt != AV_SAMPLE_FMT_NONE,
                           "%s", av_get_sample_fmt_name(*fmt));
+
+    av_bprint_init(&desc, AV_BPRINT_SIZE_AUTOMATIC);
     PRINT_CODEC_SUPPORTED(c, AV_CODEC_CONFIG_CHANNEL_LAYOUT, AVChannelLayout,
                           "channel layouts", layout, layout->nb_channels,
-                          "%s", get_channel_layout_desc(layout, desc, sizeof(desc)));
+                          "%s", get_channel_layout_desc(layout, &desc));
+    av_bprint_finalize(&desc, NULL);
 
     if (c->priv_class) {
         show_help_children(c->priv_class,

> 
> >   
> >       if (c->priv_class) {
> >           show_help_children(c->priv_class,
> > @@ -566,8 +560,14 @@ static void show_help_bsf(const char *name)
> >       }
> >   
> >       printf("Bit stream filter %s\n", bsf->name);
> > -    PRINT_CODEC_SUPPORTED(bsf, codec_ids, enum AVCodecID, "codecs",
> > -                          AV_CODEC_ID_NONE, GET_CODEC_NAME);
> > +    if (bsf->codec_ids) {
> > +        const enum AVCodecID *id = bsf->codec_ids;
> > +        printf("    Supported codecs:");
> > +        while (*id != AV_CODEC_ID_NONE) {
> > +            printf(" %s", avcodec_descriptor_get(*id)->name);
> > +            id++;
> > +        }
> > +    }
> >       if (bsf->priv_class)
> >           show_help_children(bsf->priv_class, AV_OPT_FLAG_BSF_PARAM);
> >   }
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