avformat/matroskaenc: Speed up reformatting WavPack

WavPack's blocks use a length field, so that parsing them is fast.
Therefore it makes sense to parse the block twice, once to get
the length of the output packet and once to write the actual data
instead of writing the data into a temporary buffer in a single pass.

This speeds up muxing from 1597092 to 761850 Decicycles per
write_packet call for a 2000kb/s stereo WavPack file muxed to /dev/null
with writing CRC-32 disabled.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/matroskaenc.c

@@ -2347,57 +2347,45 @@ static int mkv_blockgroup_size(int pkt_size, int track_num_size)
 }
 
 #if CONFIG_MATROSKA_MUXER
-static int mkv_strip_wavpack(const uint8_t *src, uint8_t **pdst, int *size)
+static int mkv_reformat_wavpack(MatroskaMuxContext *mkv, AVIOContext *pb,
+                                const AVPacket *pkt, int *size)
 {
-    uint8_t *dst;
-    int srclen = *size;
+    const uint8_t *src = pkt->data;
+    int srclen = pkt->size;
     int offset = 0;
     int ret;
 
-    dst = av_malloc(srclen);
-    if (!dst)
-        return AVERROR(ENOMEM);
-
     while (srclen >= WV_HEADER_SIZE) {
         WvHeader header;
 
         ret = ff_wv_parse_header(&header, src);
         if (ret < 0)
-            goto fail;
+            return ret;
         src    += WV_HEADER_SIZE;
         srclen -= WV_HEADER_SIZE;
 
-        if (srclen < header.blocksize) {
-            ret = AVERROR_INVALIDDATA;
-            goto fail;
-        }
+        if (srclen < header.blocksize)
+            return AVERROR_INVALIDDATA;
 
-        if (header.initial) {
-            AV_WL32(dst + offset, header.samples);
-            offset += 4;
-        }
-        AV_WL32(dst + offset,     header.flags);
-        AV_WL32(dst + offset + 4, header.crc);
-        offset += 8;
+        offset += 4 * !!header.initial + 8 + 4 * !(header.initial && header.final);
+        if (pb) {
+            if (header.initial)
+                avio_wl32(pb, header.samples);
+            avio_wl32(pb, header.flags);
+            avio_wl32(pb, header.crc);
 
-        if (!(header.initial && header.final)) {
-            AV_WL32(dst + offset, header.blocksize);
-            offset += 4;
-        }
+            if (!(header.initial && header.final))
+                avio_wl32(pb, header.blocksize);
 
-        memcpy(dst + offset, src, header.blocksize);
+            avio_write(pb, src, header.blocksize);
+        }
         src    += header.blocksize;
         srclen -= header.blocksize;
         offset += header.blocksize;
     }
-
-    *pdst = dst;
     *size = offset;
 
     return 0;
-fail:
-    av_freep(&dst);
-    return ret;
 }
 #endif
 
@@ -2436,8 +2424,6 @@ static int mkv_write_block(AVFormatContext *s, AVIOContext *pb,
                (AV_RB24(par->extradata) == 1 || AV_RB32(par->extradata) == 1)) {
         /* extradata is Annex B, assume the bitstream is too and convert it */
         err = ff_hevc_annexb2mp4_buf(pkt->data, &data, &size, 0, NULL);
-    } else if (par->codec_id == AV_CODEC_ID_WAVPACK) {
-        err = mkv_strip_wavpack(pkt->data, &data, &size);
     } else
 #endif
            if (par->codec_id == AV_CODEC_ID_AV1) {
@@ -3111,8 +3097,17 @@ static int mkv_init(struct AVFormatContext *s)
 
     for (i = 0; i < s->nb_streams; i++) {
         AVStream *st = s->streams[i];
+        const AVCodecParameters *const par = st->codecpar;
         mkv_track *track = &mkv->tracks[i];
 
+        switch (par->codec_id) {
+#if CONFIG_MATROSKA_MUXER
+        case AV_CODEC_ID_WAVPACK:
+            track->reformat = mkv_reformat_wavpack;
+            break;
+#endif
+        }
+
         if (s->flags & AVFMT_FLAG_BITEXACT) {
             track->uid = i + 1;
         } else {