Re: [FFmpeg-devel] [PATCH 1/2] avformat/mxf: start to add mxf_inspect_mode and skip RIP if needed sponsored by nxtedition

[Marton Balint]

On Wed, 21 Aug 2024, Marc-Antoine ARNAUD wrote:

Le sam. 17 août 2024 à 21:15, Marton Balint <c...@passwd.hu> a écrit :



On Wed, 14 Aug 2024, Marc-Antoine Arnaud wrote:

> ---
> libavformat/mxfdec.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)

Why would you want to tune this?


Hi Marton

In some MXF files, index tables are present in the first body partition or
fully in the footer partition.
This patch will skip parsing all body partitions if the index table is
coherent.

That still does not answer the "why". You want to avoid reading every 
partition pack when the file is opened? If you ignore reading the RIP 
(and consequentally force the system to do a forward parse and not read all 
partition packs in advance) then I am not sure how seeking will work, 
because even if there is a full index, you won't have a list of partitions 
and the essence body offsets for the partitions.

The quick and dirty way of forcing opening a file without reading all 
partition packs is using -seekable 0 when opening that file... Isn't 
that enough for your use case?

Something more advanced is not trivial, because you'd have to parse the 
partitions packs on demand.

Regards,
Marton



Best regards,
Marc-Antoine



Thanks,
Marton

>
> diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
> index a5863445ab5..df958819300 100644
> --- a/libavformat/mxfdec.c
> +++ b/libavformat/mxfdec.c
> @@ -321,6 +321,7 @@ typedef struct MXFContext {
>     int nb_index_tables;
>     MXFIndexTable *index_tables;
>     int eia608_extract;
> +    int mxf_inspect_mode;
> } MXFContext;
>
> /* NOTE: klv_offset is not set (-1) for local keys */
> @@ -3713,7 +3714,9 @@ static int mxf_read_header(AVFormatContext *s)
>         return AVERROR_INVALIDDATA;
>     mxf->run_in = run_in;
>
> -    mxf_read_random_index_pack(s);
> +    if (mxf->mxf_inspect_mode == 0) {
> +        mxf_read_random_index_pack(s);
> +    }
>
>     while (!avio_feof(s->pb)) {
>         const MXFMetadataReadTableEntry *metadata;
> @@ -4261,6 +4264,15 @@ static const AVOption options[] = {
>     { "eia608_extract", "extract eia 608 captions from s436m track",
>       offsetof(MXFContext, eia608_extract), AV_OPT_TYPE_BOOL, {.i64 =
0}, 0, 1,
>       AV_OPT_FLAG_DECODING_PARAM },
> +    { "mxf_inspect_mode", "the way to inspect MXF file",
> +      offsetof(MXFContext, mxf_inspect_mode), AV_OPT_TYPE_INT, {.i64 =
0}, 0, 1,
> +      AV_OPT_FLAG_DECODING_PARAM, .unit = "mxf_inspect_mode" },
> +    { "rip", "Parse RIP, then every body partition",
> +      0, AV_OPT_TYPE_CONST, {.i64 = 0}, INT_MIN, INT_MAX,
> +      AV_OPT_FLAG_DECODING_PARAM, .unit = "mxf_inspect_mode" },
> +    { "header", "Parse Header, first partition and next partitions if
needed",
> +      0, AV_OPT_TYPE_CONST, {.i64 = 1}, INT_MIN, INT_MAX,
> +      AV_OPT_FLAG_DECODING_PARAM, .unit = "mxf_inspect_mode" },
>     { NULL },
> };
>
> --
> 2.39.3 (Apple Git-146)
>
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