On Wed, 9 Apr 2014 18:50:05 +0200, Alessandro Ghedini <[email protected]>
wrote:
> ---
> libavformat/mp3dec.c | 57
> ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 57 insertions(+)
>
> diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
> index 1ab5159..e33f524 100644
> --- a/libavformat/mp3dec.c
> +++ b/libavformat/mp3dec.c
> @@ -132,7 +132,17 @@ static void read_xing_toc(AVFormatContext *s, int64_t
> filesize, int64_t duration
> static void mp3_parse_info_tag(AVFormatContext *s, AVStream *st,
> MPADecodeHeader *c, uint32_t spf)
> {
> +#define LAST_BITS(k, n) ((k) & ((1 << (n)) - 1))
> +#define MIDDLE_BITS(k, m, n) LAST_BITS((k) >> (m), ((n) - (m)))
> +
> + float f;
> uint32_t v;
> +
> + char version[10];
> +
> + uint32_t peak = 0;
> + int32_t r_gain = INT32_MIN, a_gain = INT32_MIN;
> +
> MP3DecContext *mp3 = s->priv_data;
> const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}};
>
> @@ -152,6 +162,53 @@ static void mp3_parse_info_tag(AVFormatContext *s,
> AVStream *st,
> (AVRational){spf, c->sample_rate},
> st->time_base));
> }
> +
> + avio_skip(s->pb, 3);
> +
> + /* VBR quality */
> + avio_r8(s->pb);
Doesn't matter much since we ignore the value, but isn't vbr quality this whole
32bit number?
> +
> + /* Encoder short version string */
> + avio_get_str(s->pb, 9, version, 10);
^^
sizeof(version) please
Also, perhaps we should export this as 'encoder' in the stream metadata (not in
global, so we don't conflict with whatever is read from the ID3 tag).
And I wonder if it's safe to unconditionally assume the tag is in the LAME
format. IIUC, it can be just the XING tag with garbage/zeroes filling the rest
of the frame?
Is there some way to check that the tag is really in the LAME format?
> +
> + /* Info Tag revision + VBR method */
> + avio_r8(s->pb);
> +
> + /* Lowpass filter value */
> + avio_r8(s->pb);
> +
> + /* ReplayGain peak */
> + v = avio_rb32(s->pb);
> + f = (v << 5) / (float) (1 << 28);
http://gabriel.mp3-tech.org/mp3infotag.html says this value is stored as float
(nb: people doing such stuff need to be stabbed with a rusty spork repeatedly),
so perhaps use av_int2float()?
> +
> + if (f > 0)
> + peak = f * 100000;
> +
> + v = avio_rb16(s->pb);
> +
> + /* Radio ReplayGain */
> + if (MIDDLE_BITS(v, 13, 15) == 1) {
> + f = MIDDLE_BITS(v, 0, 8) / 10.f;
Why /10? You can remove a zero from the multiplication below instead, no?
That will also avoid the evil inexact float arithmetics.
--
Anton Khirnov
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