static int mp3_write_xing(AVFormatContext *s) { MP3Context *mp3 = s->priv_data; AVCodecContext *codec = s->streams[mp3->audio_stream_idx]->codec; AVDictionaryEntry *enc = av_dict_get(s->streams[mp3->audio_stream_idx]->metadata, "encoder", NULL, 0); AVIOContext *dyn_ctx; int32_t header; MPADecodeHeader mpah; int srate_idx, i, channels; int bitrate_idx; int best_bitrate_idx = -1; int best_bitrate_error = INT_MAX; int ret; int ver = 0; int bytes_needed; if (!s->pb->seekable || !mp3->write_xing) return 0; for (i = 0; i < FF_ARRAY_ELEMS(avpriv_mpa_freq_tab); i++) { const uint16_t base_freq = avpriv_mpa_freq_tab[i]; if (codec->sample_rate == base_freq) ver = 0x3; // MPEG 1 else if (codec->sample_rate == base_freq / 2) ver = 0x2; // MPEG 2 else if (codec->sample_rate == base_freq / 4) ver = 0x0; // MPEG 2.5 else continue; srate_idx = i; break; } if (i == FF_ARRAY_ELEMS(avpriv_mpa_freq_tab)) { av_log(s, AV_LOG_WARNING, "Unsupported sample rate, not writing Xing header.\n"); return -1; } switch (codec->channels) { case 1: channels = MPA_MONO; break; case 2: channels = MPA_STEREO; break; default: av_log(s, AV_LOG_WARNING, "Unsupported number of channels, " "not writing Xing header.\n"); return -1; } /* dummy MPEG audio header */ header = 0xffU << 24; // sync header |= (0x7 << 5 | ver << 3 | 0x1 << 1 | 0x1) << 16; // sync/audio-version/layer 3/no crc*/ header |= (srate_idx << 2) << 8; header |= channels << 6; for (bitrate_idx = 1; bitrate_idx < 15; bitrate_idx++) { int bit_rate = 1000 * avpriv_mpa_bitrate_tab[ver != 3][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; } } av_assert0(best_bitrate_idx >= 0); for (bitrate_idx = best_bitrate_idx; ; bitrate_idx++) { int32_t mask = bitrate_idx << (4 + 8); if (15 == bitrate_idx) return -1; header |= mask; avpriv_mpegaudio_decode_header(&mpah, header); mp3->xing_offset = xing_offtbl[mpah.lsf == 1][mpah.nb_channels == 1] + 4; bytes_needed = mp3->xing_offset + XING_SIZE; if (bytes_needed <= mpah.frame_size) break; header &= ~mask; } ret = avio_open_dyn_buf(&dyn_ctx); if (ret < 0) return ret; avio_wb32(dyn_ctx, header); ffio_fill(dyn_ctx, 0, mp3->xing_offset - 4); ffio_wfourcc(dyn_ctx, "Xing"); avio_wb32(dyn_ctx, 0x01 | 0x02 | 0x04 | 0x08); // frames / size / TOC / vbr scale mp3->size = mpah.frame_size; mp3->want=1; mp3->seen=0; mp3->pos=0; avio_wb32(dyn_ctx, 0); // frames avio_wb32(dyn_ctx, 0); // size // TOC for (i = 0; i < XING_TOC_SIZE; i++) avio_w8(dyn_ctx, (uint8_t)(255 * i / XING_TOC_SIZE)); // vbr quality // we write it, because some (broken) tools always expect it to be present avio_wb32(dyn_ctx, 0); // encoder short version string if (enc) { uint8_t encoder_str[9] = { 0 }; if ( strlen(enc->value) > sizeof(encoder_str) && !strcmp("Lavc libmp3lame", enc->value)) { memcpy(encoder_str, "Lavf lame", 9); } else memcpy(encoder_str, enc->value, FFMIN(strlen(enc->value), sizeof(encoder_str))); avio_write(dyn_ctx, encoder_str, sizeof(encoder_str)); } else avio_write(dyn_ctx, "Lavf\0\0\0\0\0", 9); avio_w8(dyn_ctx, 0); // tag revision 0 / unknown vbr method avio_w8(dyn_ctx, 0); // unknown lowpass filter value ffio_fill(dyn_ctx, 0, 8); // empty replaygain fields avio_w8(dyn_ctx, 0); // unknown encoding flags avio_w8(dyn_ctx, 0); // unknown abr/minimal bitrate // encoder delay if (codec->initial_padding - 528 - 1 >= 1 << 12) { av_log(s, AV_LOG_WARNING, "Too many samples of initial padding.\n"); } avio_wb24(dyn_ctx, FFMAX(codec->initial_padding - 528 - 1, 0)<<12); avio_w8(dyn_ctx, 0); // misc avio_w8(dyn_ctx, 0); // mp3gain avio_wb16(dyn_ctx, 0); // preset // audio length and CRCs (will be updated later) avio_wb32(dyn_ctx, 0); // music length avio_wb16(dyn_ctx, 0); // music crc avio_wb16(dyn_ctx, 0); // tag crc ffio_fill(dyn_ctx, 0, mpah.frame_size - bytes_needed); mp3->xing_frame_size = avio_close_dyn_buf(dyn_ctx, &mp3->xing_frame); mp3->xing_frame_offset = avio_tell(s->pb); avio_write(s->pb, mp3->xing_frame, mp3->xing_frame_size); mp3->audio_size = mp3->xing_frame_size; return 0; }