On 09/04/14 18:22, Alessandro Ghedini wrote:
> From: Michael Niedermayer <[email protected]>
>
> Instead of using a fixed bitrate_idx, try to calculate a matching bitrate for
> the XING header.
>
> Using a fixed bitrate_idx causes tools such as file(1) and mediainfo(1) to
> report wrong bitrate and bitrate mode when using CBR.
>
> Bug: https://bugs.debian.org/736088
> ---
> This includes a few clean-ups and the suggestions from Luca for the bit_rate
> and lsf calculations.
>
> libavformat/mp3enc.c | 46 +++++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 39 insertions(+), 7 deletions(-)
>
> diff --git a/libavformat/mp3enc.c b/libavformat/mp3enc.c
> index 46889fc..6f969c4 100644
> --- a/libavformat/mp3enc.c
> +++ b/libavformat/mp3enc.c
> @@ -119,8 +119,11 @@ static void mp3_write_xing(AVFormatContext *s)
> MPADecodeHeader mpah;
> int srate_idx, i, channels;
> int bitrate_idx;
> + int best_bitrate_idx;
> + int best_bitrate_error = INT_MAX;
> int xing_offset;
> int ver = 0;
> + int lsf, bytes_needed;
>
> if (!s->pb->seekable || !mp3->write_xing)
> return;
> @@ -150,21 +153,51 @@ static void mp3_write_xing(AVFormatContext *s)
> return;
> }
>
> - /* 64 kbps frame, should be large enough */
> - bitrate_idx = (ver == 3) ? 5 : 8;
> -
> /* dummy MPEG audio header */
> header = 0xff << 24; // sync
> header |= (0x7 << 5 | ver << 3 | 0x1 << 1 | 0x1) << 16; //
> sync/audio-version/layer 3/no crc*/
> - header |= (bitrate_idx << 4 | srate_idx << 2) << 8;
> + header |= (srate_idx << 2) << 8;
> header |= channels << 6;
> +
> + lsf = (header & (1 << 20) && header & (1 << 19)) ? 0 : 1;
lsf = !(header & (1 << 20) && header & (1 << 19));
might be more compact
> + for (bitrate_idx = 1; bitrate_idx < 15; bitrate_idx++) {
> + int bit_rate = 1000 * avpriv_mpa_bitrate_tab[lsf][3 -
> 1][bitrate_idx];
> + int error = FFABS(bit_rate - codec->bit_rate);
> +
> + if (error < best_bitrate_error){
> + best_bitrate_error = error;
> + best_bitrate_idx = bitrate_idx;
> + }
> + }
> +
> + for (bitrate_idx = best_bitrate_idx; bitrate_idx < 15; bitrate_idx++) {
> + int32_t mask = bitrate_idx << (4 + 8);
> + header |= mask;
> +
> + avpriv_mpegaudio_decode_header(&mpah, header);
> +
> + if (bytes_needed <= mpah.frame_size)
> + break;
> +
> + header &= ~mask;
> + }
> +
> avio_wb32(s->pb, header);
>
> avpriv_mpegaudio_decode_header(&mpah, header);
>
> av_assert0(mpah.frame_size >= XING_MAX_SIZE);
>
> - xing_offset = xing_offtbl[ver != 3][codec->channels == 1];
> ffio_fill(s->pb, 0, xing_offset);
> mp3->xing_offset = avio_tell(s->pb);
> ffio_wfourcc(s->pb, "Xing");
> @@ -180,8 +213,7 @@ static void mp3_write_xing(AVFormatContext *s)
> for (i = 0; i < XING_TOC_SIZE; i++)
> avio_w8(s->pb, 255 * i / XING_TOC_SIZE);
>
> - mpah.frame_size -= 4 + xing_offset + 4 + 4 + 4 + 4 + XING_TOC_SIZE;
> - ffio_fill(s->pb, 0, mpah.frame_size);
> + ffio_fill(s->pb, 0, mpah.frame_size - bytes_needed);
> }
The rest looks fine to me, no need to send an update I think.
lu
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