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

[James Almer <jamrial@gmail.com>]

On 4/6/2024 8:38 AM, Niklas Haas wrote:
> 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);

I don't think this is needed if it's called immediately after 
av_bprint_init().

> +    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);

Yeah, this is good. Thanks.

>   
>       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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