[FFmpeg-devel] [PATCH v2 4/4] avformat/libopenmpt: Probe file format from file data if possible

[Carl Eugen Hoyos]

2018-01-10 12:18 GMT+01:00 Jörn Heusipp <osmanx at problemloesungsmaschine.de>:
> When building with libopenmpt 0.3, use the libopenmpt file header
> probing functions for probing. libopenmpt probing functions are
> allocation-free and designed to be as fast as possible.
>
> For libopenmpt 0.2, or when libopenmpt 0.3 file header probing cannot
> probe successfully due to too small probe buffer, test the filename
> against the file extensions supported by the libopenmpt library that
> is actually linked, instead of relying on a hard-coded file extension
> list. File extension testing is also allocation-free and designed to
> be fast in libopenmpt. Avoiding a hard-coded file extension list is
> useful because later libopenmpt versions will likely add support for
> more module file formats.
>
> libopenmpt file header probing is tested regularly against the FATE
> suite and other diverse file collections by libopenmpt upstream in
> order to avoid false positives.
>
> FATE passes with './configure --enable-libopenmpt' as well as with
> './configure --enable-libopenmpt --enable-libmodplug'.
>
> libopenmpt probing adds about 5%..10% cpu time (depending on precise
> usage pattern and host CPU and compiler version used for libopenmpt)
> compared to all current internal FFmpeg probing functions combined in
> tools/probetest for all of its module formats combined (currently 41
> modules formats in libopenmpt 0.3.4 and 234 file formats in FFmpeg).
>
> Signed-off-by: Jörn Heusipp <osmanx at problemloesungsmaschine.de>
> ---
>  libavformat/libopenmpt.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 57 insertions(+)
>
> diff --git a/libavformat/libopenmpt.c b/libavformat/libopenmpt.c
> index 5efbdc4..42b78fb 100644
> --- a/libavformat/libopenmpt.c
> +++ b/libavformat/libopenmpt.c
> @@ -218,6 +218,62 @@ static int read_seek_openmpt(AVFormatContext *s, int stream_idx, int64_t ts, int
>      return 0;
>  }
>
> +static int probe_openmpt_extension(AVProbeData *p)
> +{
> +    const char *ext;
> +    if (p->filename) {
> +        ext = strrchr(p->filename, '.');
> +        if (ext && strlen(ext + 1) > 0) {
> +            ext++;  /* skip '.' */
> +            if (openmpt_is_extension_supported(ext) == 1)
> +                return AVPROBE_SCORE_EXTENSION;
> +        }
> +    }
> +    return 0;
> +}
> +
> +static int read_probe_openmpt(AVProbeData *p)
> +{
> +#if OPENMPT_API_VERSION_AT_LEAST(0,3,0)
> +    int probe_result;
> +    if (p->buf && p->buf_size > 0) {
> +        probe_result = openmpt_probe_file_header_without_filesize(
> +                           OPENMPT_PROBE_FILE_HEADER_FLAGS_DEFAULT,
> +                           p->buf, p->buf_size,
> +                           &openmpt_logfunc, NULL, NULL, NULL, NULL, NULL);
> +        if (probe_result == OPENMPT_PROBE_FILE_HEADER_RESULT_SUCCESS) {
> +            /* As probing here relies on code external to FFmpeg, do not return
> +             * AVPROBE_SCORE_MAX in order to reduce the impact in the rare
> +             * cases of false positives.
> +             */
> +            return AVPROBE_SCORE_MIME + 1;
> +        } else if (probe_result == OPENMPT_PROBE_FILE_HEADER_RESULT_WANTMOREDATA) {

> +            if (probe_openmpt_extension(p) > 0) {
> +                return AVPROBE_SCORE_EXTENSION;

I don't think this is a good idea because it means that a high score is
reported for WANTMOREDATA.

Carl Eugen