static int ac3_decode_frame(AVCodecContext * avctx, void *data, int *data_size, const uint8_t *buf, int buf_size) { AC3DecodeContext *s = avctx->priv_data; int16_t *out_samples = (int16_t *)data; int i, blk, ch, err; /* initialize the GetBitContext with the start of valid AC-3 Frame */ if (s->input_buffer) { /* copy input buffer to decoder context to avoid reading past the end of the buffer, which can be caused by a damaged input stream. */ memcpy(s->input_buffer, buf, FFMIN(buf_size, AC3_MAX_FRAME_SIZE)); init_get_bits(&s->gbc, s->input_buffer, buf_size * 8); } else { init_get_bits(&s->gbc, buf, buf_size * 8); } /* parse the syncinfo */ err = ac3_parse_header(s); if(err) { switch(err) { case AC3_PARSE_ERROR_SYNC: av_log(avctx, AV_LOG_ERROR, "frame sync error : cannot use error concealment\n"); return -1; case AC3_PARSE_ERROR_BSID: av_log(avctx, AV_LOG_ERROR, "invalid bitstream id\n"); break; case AC3_PARSE_ERROR_SAMPLE_RATE: av_log(avctx, AV_LOG_ERROR, "invalid sample rate\n"); break; case AC3_PARSE_ERROR_FRAME_SIZE: av_log(avctx, AV_LOG_ERROR, "invalid frame size\n"); break; case AC3_PARSE_ERROR_FRAME_TYPE: av_log(avctx, AV_LOG_ERROR, "invalid frame type\n"); break; default: av_log(avctx, AV_LOG_ERROR, "invalid header\n"); break; } } /* check that reported frame size fits in input buffer */ if(s->frame_size > buf_size) { av_log(avctx, AV_LOG_ERROR, "incomplete frame\n"); return -1; } /* check for crc mismatch */ if(!err && avctx->error_resilience >= FF_ER_CAREFUL) { if(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, &buf[2], s->frame_size-2)) { av_log(avctx, AV_LOG_ERROR, "frame CRC mismatch\n"); err = 1; } } /* if frame is ok, set audio parameters */ if (!err) { avctx->sample_rate = s->sample_rate; avctx->bit_rate = s->bit_rate; /* channel config */ s->out_channels = s->channels; s->output_mode = s->channel_mode; if(s->lfe_on) s->output_mode |= AC3_OUTPUT_LFEON; if (avctx->request_channels > 0 && avctx->request_channels <= 2 && avctx->request_channels < s->channels) { s->out_channels = avctx->request_channels; s->output_mode = avctx->request_channels == 1 ? AC3_CHMODE_MONO : AC3_CHMODE_STEREO; } avctx->channels = s->out_channels; /* set downmixing coefficients if needed */ if(s->channels != s->out_channels && !((s->output_mode & AC3_OUTPUT_LFEON) && s->fbw_channels == s->out_channels)) { set_downmix_coeffs(s); } } else if (!s->out_channels) { s->out_channels = avctx->channels; if(s->out_channels < s->channels) s->output_mode = s->out_channels == 1 ? AC3_CHMODE_MONO : AC3_CHMODE_STEREO; } /* parse the audio blocks */ for (blk = 0; blk < NB_BLOCKS; blk++) { if (!err && ac3_parse_audio_block(s, blk)) { av_log(avctx, AV_LOG_ERROR, "error parsing the audio block\n"); } for (i = 0; i < 256; i++) for (ch = 0; ch < s->out_channels; ch++) *(out_samples++) = s->int_output[ch][i]; } *data_size = NB_BLOCKS * 256 * avctx->channels * sizeof (int16_t); return s->frame_size; }