[FFmpeg-devel] [PATCH v2] avcodec/ffv1: Implement CRC with non zero initial and final value

[Michael Niedermayer]

Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
---
 libavcodec/ffv1.h    |  1 +
 libavcodec/ffv1dec.c | 10 ++++++----
 libavcodec/ffv1enc.c | 12 +++++++++---
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/libavcodec/ffv1.h b/libavcodec/ffv1.h
index 9aa04529228..c22325d2510 100644
--- a/libavcodec/ffv1.h
+++ b/libavcodec/ffv1.h
@@ -118,6 +118,7 @@ typedef struct FFV1Context {
     int64_t picture_number;
     int key_frame;
     ProgressFrame picture, last_picture;
+    uint32_t crcref;
 
     const AVFrame *cur_enc_frame;
     int plane_count;
diff --git a/libavcodec/ffv1dec.c b/libavcodec/ffv1dec.c
index 0afdeabd915..b4d719a7eec 100644
--- a/libavcodec/ffv1dec.c
+++ b/libavcodec/ffv1dec.c
@@ -502,15 +502,17 @@ static int read_extra_header(FFV1Context *f)
 
     if (f->version > 2) {
         f->ec = get_symbol(&c, state, 0);
+        if (f->ec >= 2)
+            f->crcref = 0x7a8c4079;
         if (f->micro_version > 2)
             f->intra = get_symbol(&c, state, 0);
     }
 
     if (f->version > 2) {
         unsigned v;
-        v = av_crc(av_crc_get_table(AV_CRC_32_IEEE), 0,
+        v = av_crc(av_crc_get_table(AV_CRC_32_IEEE), f->crcref,
                    f->avctx->extradata, f->avctx->extradata_size);
-        if (v || f->avctx->extradata_size < 4) {
+        if (v != f->crcref || f->avctx->extradata_size < 4) {
             av_log(f->avctx, AV_LOG_ERROR, "CRC mismatch %X!\n", v);
             return AVERROR_INVALIDDATA;
         }
@@ -948,8 +950,8 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *rframe,
         buf_p -= v;
 
         if (f->ec) {
-            unsigned crc = av_crc(av_crc_get_table(AV_CRC_32_IEEE), 0, buf_p, v);
-            if (crc) {
+            unsigned crc = av_crc(av_crc_get_table(AV_CRC_32_IEEE), f->crcref, buf_p, v);
+            if (crc != f->crcref) {
                 int64_t ts = avpkt->pts != AV_NOPTS_VALUE ? avpkt->pts : avpkt->dts;
                 av_log(f->avctx, AV_LOG_ERROR, "slice CRC mismatch %X!", crc);
                 if (ts != AV_NOPTS_VALUE && avctx->pkt_timebase.num) {
diff --git a/libavcodec/ffv1enc.c b/libavcodec/ffv1enc.c
index a6f405289eb..2267a01816e 100644
--- a/libavcodec/ffv1enc.c
+++ b/libavcodec/ffv1enc.c
@@ -458,7 +458,7 @@ static int write_extradata(FFV1Context *f)
     }
 
     f->avctx->extradata_size = ff_rac_terminate(&c, 0);
-    v = av_crc(av_crc_get_table(AV_CRC_32_IEEE), 0, f->avctx->extradata, f->avctx->extradata_size);
+    v = av_crc(av_crc_get_table(AV_CRC_32_IEEE), f->crcref, f->avctx->extradata, f->avctx->extradata_size) ^ (f->crcref ? 0x8CD88196 : 0);
     AV_WL32(f->avctx->extradata + f->avctx->extradata_size, v);
     f->avctx->extradata_size += 4;
 
@@ -544,7 +544,13 @@ static av_cold int encode_init(AVCodecContext *avctx)
     }
 
     if (s->ec < 0) {
-        s->ec = (s->version >= 3);
+        if (s->version >= 4) {
+            s->ec = 2;
+            s->crcref = 0x7a8c4079;
+        } else if (s->version >= 3) {
+            s->ec = 1;
+        } else
+            s->ec = 0;
     }
 
     // CRC requires version 3+
@@ -1230,7 +1236,7 @@ static int encode_frame(AVCodecContext *avctx, AVPacket *pkt,
         if (f->ec) {
             unsigned v;
             buf_p[bytes++] = 0;
-            v = av_crc(av_crc_get_table(AV_CRC_32_IEEE), 0, buf_p, bytes);
+            v = av_crc(av_crc_get_table(AV_CRC_32_IEEE), f->crcref, buf_p, bytes) ^ (f->crcref ? 0x8CD88196 : 0);
             AV_WL32(buf_p + bytes, v);
             bytes += 4;
         }
-- 
2.46.1