twinvq: set block align for codecs and use it in size checks

This both allows factoring out size check for both MetaSound and TwinVQ-VQF
decoders and fixes the situation when there are several MetaSound frames
stuffed together (that happens in 8kHz @ 8kbps MetaSound in ASF for example).

libavcodec/metasound.c

@@ -170,12 +170,6 @@ static int metasound_read_bitstream(AVCodecContext *avctx, TwinVQContext *tctx,
     GetBitContext gb;
     int i, j, k;
 
-    if (buf_size * 8 < avctx->bit_rate * mtab->size / avctx->sample_rate) {
-        av_log(avctx, AV_LOG_ERROR,
-               "Frame too small (%d bytes). Truncated file?\n", buf_size);
-        return AVERROR(EINVAL);
-    }
-
     init_get_bits(&gb, buf, buf_size * 8);
 
     bits->window_type = get_bits(&gb, TWINVQ_WINDOW_TYPE_BITS);
@@ -323,6 +317,9 @@ static av_cold int metasound_decode_init(AVCodecContext *avctx)
         return AVERROR(ENOSYS);
     }
 
+    avctx->block_align = (avctx->bit_rate * tctx->mtab->size
+                                          / avctx->sample_rate + 7) / 8;
+
     tctx->codec          = TWINVQ_CODEC_METASOUND;
     tctx->read_bitstream = metasound_read_bitstream;
     tctx->dec_bark_env   = dec_bark_env;

libavcodec/twinvq.c

@@ -491,6 +491,12 @@ int ff_twinvq_decode_frame(AVCodecContext *avctx, void *data,
         out = (float **)frame->extended_data;
     }
 
+    if (buf_size < avctx->block_align) {
+        av_log(avctx, AV_LOG_ERROR,
+               "Frame too small (%d bytes). Truncated file?\n", buf_size);
+        return AVERROR(EINVAL);
+    }
+
     if ((ret = tctx->read_bitstream(avctx, tctx, buf, buf_size)) < 0)
         return ret;
 
@@ -508,7 +514,7 @@ int ff_twinvq_decode_frame(AVCodecContext *avctx, void *data,
 
     *got_frame_ptr = 1;
 
-    return buf_size;
+    return avctx->block_align;
 }
 
 /**

libavcodec/twinvqdec.c

@@ -258,12 +258,6 @@ static int twinvq_read_bitstream(AVCodecContext *avctx, TwinVQContext *tctx,
     GetBitContext gb;
     int i, j, k;
 
-    if (buf_size * 8 < avctx->bit_rate * mtab->size / avctx->sample_rate + 8) {
-        av_log(avctx, AV_LOG_ERROR,
-               "Frame too small (%d bytes). Truncated file?\n", buf_size);
-        return AVERROR(EINVAL);
-    }
-
     init_get_bits(&gb, buf, buf_size * 8);
     skip_bits(&gb, get_bits(&gb, 8));
 
@@ -398,6 +392,9 @@ static av_cold int twinvq_decode_init(AVCodecContext *avctx)
         return -1;
     }
 
+    avctx->block_align = (avctx->bit_rate * tctx->mtab->size
+                                          / avctx->sample_rate + 15) / 8;
+
     tctx->codec          = TWINVQ_CODEC_VQF;
     tctx->read_bitstream = twinvq_read_bitstream;
     tctx->dec_bark_env   = dec_bark_env;